Pianc - Scour 2015

PIANC

Report n° 180 - 2015

‘Setting the Course’ 

GUIDELINES FOR PROTECTING BERTHING STRUCTURES FROM SCOUR CAUSED BY SHIPS The World Association for Waterborne Tr Transpor ansportt Infrastructure

PIANC PIANC REPOR REPORT T N° 180 MARITIME NAVIGATION COMMISSION

GUIDELINES FOR PROTECTING BERTHING STRUCTURES FROM SCOUR CAUSED BY SHIPS 2015

PIANC has Technical Commissions concerned with inland waterways and ports (InCom), coastal and ocean waterways (including ports and harbours) (MarCom), environmental aspects (EnviCom) and sport and pleasure navigation (RecCom). This report has been produced by an international Working Group convened by the Maritime Navigation Commission (MarCom). Members of the Working Group represent several countries and are acknowledg acknowledged ed experts in their profession. The objective of this report is to provide information and recommendations on good practice. Conformity is not obligatory and engineering judgement should be used in its application,, especially in special circumstances. application circumstances. This report should be seen as an expert guidance and state of the art on this particular subject. PIANC is not a certifying body and disclaims all responsibility responsibility in case this report should be presented as an official standard and/or as a certification.

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TABLE OF CONTENTS 1. 2.

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FOREWORD &TERMS OF REFERENCE................................................................................... 1 1.1. FOREWORD ....................................................................................................................... 1 1.2. TERMS OF REFERENCE....................................................................................................... 1 MEMBERS OF PIANC MARCOM WG 180 (48) .......................................................................... 3 2.1. MEMBERS .......................................................................................................................... 3 2.2. CORRESPONDING MEMBERS................................................................................................ 4 2.3. MEETINGS ......................................................................................................................... 5 2.4. ACKNOWLEDGEMENT .......................................................................................................... 5 INTRODUCTION ........................................................................................................................ 6 3.1. AIM OF THE REPORT .......................................................................................................... 6 3.2. STRUCTURE OF THE REPORT .............................................................................................. 6 3.3. RELATED DOCUMENTS ........................................................................................................ 6 3.4. DEFINITIONS AND SYMBOLS ................................................................................................. 7 QUAY STRUCTURES ................................................................................................................ 9 4.1. INTRODUCTION ................................................................................................................... 9 4.2. C ATEGORIES OF BERTH STRUCTURES RELEVANT TO PROPULSION ACTIONS.......................... 10 4.2.1. Solid Berth Structures .............................................................................................. 10 4.2.2. Open Berth Structures ............................................................................................. 13 4.2.3. Hybrid Structures ..................................................................................................... 15 4.2.4. Other Berth Types or Structures .............................................................................. 15 4.2.5. Modified Structures.................................................................................................. 15 4.2.6. Future Developments .............................................................................................. 16 4.2.6.1. INTRODUCTION ................................................................................................... 16 4.2.6.2. TRENDS WHICH INFLUENCE THE DESIGN OF QUAY W ALLS ...................................... 17 4.2.6.3. RETHINKING ECONOMICAL, DESIGN AND USAGE LIFE TIME ..................................... 17 4.2.6.4. C ARGO H ANDLING DEVELOPMENT ........................................................................ 18 4.2.6.5. EXAMPLES OF POSSIBLE FUTURE DESIGNS........................................................... 19 4.3. M ATERIAL TYPES OF BERTH STRUCTURES ......................................................................... 21 4.4. SOIL AND GEOTECHNICAL ASPECTS RELEVANT TO BERTH STRUCTURES AND VESSEL PROPULSION SYSTEMS ............................................................................................................ 21 4.5. VESSEL TYPES RELEVANT TO BERTH STRUCTURES AND PROPULSION ACTIONS ..................... 21 4.6. SPECIFIC ELEMENTS OF BERTH STRUCTURES RELEVANT TO PROPULSION ACTIONS ............... 22 4.6.1. Corners ................................................................................................................... 22 4.6.2. Transition Between One Structure Type and Another ............................................... 22 4.6.3. Transition In One of The Main Structure Characteristics ........................................... 23 4.6.4. Berth Pockets and Other Irregularities...................................................................... 23 PROPULSION SYTEMS ........................................................................................................... 25 5.1. OVERVIEW OF DIFFERENT TYPES ...................................................................................... 25 5.2. TYPES OF PROPELLERS .................................................................................................... 25 5.2.1. Fixed Pitch Propeller (Fpp) ...................................................................................... 25 5.2.2. Controllable Pitch Propeller (Cpp) ............................................................................ 26 5.2.3. Contra Rotating Propeller (Crp). ............................................................................... 27 5.2.4. Ducted Propellers .................................................................................................... 27 5.2.5. Transverse Thruster ................................................................................................ 28 5.2.6. Azimuthal Thruster................................................................................................... 28 5.2.6.1. DUCTED AZIMUTHAL THRUSTERS ......................................................................... 28 5.2.6.2. NON-DUCTED AZIMUTHAL THRUSTERS ................................................................. 29 5.2.6.3. DOUBLE NON-DUCTED AZIMUTHAL THRUSTERS ..................................................... 29 5.3. OTHER THRUSTER SYSTEMS ............................................................................................. 30 5.3.1. Cycloidal Propeller................................................................................................... 30 5.3.2. Water Jets ............................................................................................................... 31 5.3.3. Pump Jet Thrusters ................................................................................................. 33 5.4. RELATIONSHIP BETWEEN PROPULSION CHARACTERISTICS AND VESSEL DIMENSIONS ............. 36 5.4.1. Container Vessels ................................................................................................... 36 5.4.2. Roro Vessels ........................................................................................................... 39

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5.4.3. Tankers................................................................................................................... 39 5.4.4. Fast Ferries with Water Jet Propulsion ..................................................................... 40 5.4.5. Cruise Vessels ........................................................................................................ 41 5.4.6. Supply Vessel, Tugs ................................................................................................ 41 5.4.7. Propulsion Systems Of Inland Vessels ..................................................................... 42 5.4.8. General Relationships ............................................................................................. 44 5.5. FUTURE DEVELOPMENTS .................................................................................................. 45 BERTHING AND DEPARTURE PROCEDURES....................................................................... 47 6.1. GENERAL DESCRIPTION .................................................................................................... 47 6.2. APPLIED ENGINE POWER DURING BERTHING M ANOEUVRES.................................................. 48 DAMAGE AND FAILURE MECHANISMS ................................................................................. 53 7.1. D AMAGE .......................................................................................................................... 53 7.2. F AILURE MECHANISMS ...................................................................................................... 54 7.2.1. Failure Mechanisms For Solid Structures ................................................................. 54 7.2.2. Failure Mechanisms For Open Structures ................................................................ 56 VELOCITY DISTRIBUTION ...................................................................................................... 59 8.1. INTRODUCTION ................................................................................................................. 59 8.2. FLOW VELOCITIES IN TRANSVERSE THRUSTER JETS ............................................................ 62 8.2.1. General Equations................................................................................................... 62 8.2.2. German And Dutch Approach .................................................................................. 64 8.2.2.1. VERTICAL W ALLS ............................................................................................... 64 8.2.2.2. SLOPES ............................................................................................................. 66 8.2.2.3. INCLINED W ALLS ................................................................................................ 67 8.2.2.4. OPEN QUAY STRUCTURES................................................................................... 69 8.2.3. Transverse Thruster Jets Affecting Embankments ................................................... 70 8.2.4. Multiple Transverse Thrusters .................................................................................. 72 8.3. FLOW VELOCITIES IN JETS OF M AIN PROPULSION SYSTEMS ................................................. 72 8.3.1. Introduction – General Equations ............................................................................. 72 8.3.2. German and Dutch Approach .................................................................................. 73 8.3.3. Specific Conditions for Azipods and Azimuthal Thrusters ......................................... 75 8.3.4. Other Propulsion Systems ....................................................................................... 76 8.3.4.1. W ATER JETS ...................................................................................................... 76 8.3.4.2. VOITH SCHNEIDER .............................................................................................. 77 8.3.4.3. PUMP JETS ........................................................................................................ 78 8.3.5. Special Aspects ....................................................................................................... 79 8.3.5.1. MULTIPLE JETS .................................................................................................. 79 8.3.5.2. RUDDER EFFECT ................................................................................................ 81 8.4. NUMERICAL MODELS ........................................................................................................ 81 MATERIALS AND TECHNOLOGIES ........................................................................................ 84 9.1. OVERVIEW ....................................................................................................................... 84 9.2. ROCK .............................................................................................................................. 84 9.2.1. Material ................................................................................................................... 84 9.2.2. Properties................................................................................................................ 84 9.3. ROCK GROUTED W ITH LIQUID ASPHALT .............................................................................. 85 9.3.1. Material ................................................................................................................... 85 9.3.1.1. STONE CONFINEMENT. ........................................................................................ 85 9.3.1.2. P ARTIAL GROUTING ............................................................................................ 85 9.3.1.3. ‘FULL AND S ATURATED’ GROUTING ...................................................................... 85 9.3.2. Properties................................................................................................................ 85 9.4. ROCK GROUTED W ITH HYDRO CONCRETE  .......................................................................... 86 9.5. CONCRETE BLOCK M ATTRESSES ....................................................................................... 86 9.5.1. Material ................................................................................................................... 86 9.5.2. Properties................................................................................................................ 87 9.6. CONCRETE SLABS ............................................................................................................ 87 9.6.1. Material ................................................................................................................... 87 9.6.2. Properties................................................................................................................ 87 9.7. CONCRETE M ATTRESSES .................................................................................................. 89 9.7.1. Material ................................................................................................................... 89

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9.7.2. Properties................................................................................................................ 90 9.8. FIBROUS OPEN STONE ASPHALT M ATTRESSES ................................................................... 91 9.8.1. Material ................................................................................................................... 91 9.8.2. Properties................................................................................................................ 93 9.9. GEOSYNTHETICS AND GEOSYSTEMS .................................................................................. 93 9.9.1. Material ................................................................................................................... 93 9.9.2. Properties................................................................................................................ 95 9.10. SOFT SOIL IMPROVEMENT ............................................................................................... 95 DESIGN OF SCOUR AND BED PROTECTIONS .................................................................. 96 10.1. DESIGN PHILOSOPHY ...................................................................................................... 96 10.2. SCOUR .......................................................................................................................... 98 10.2.1. Scour by Transverse Thrusters .............................................................................. 98 10.2.1.1. CLOSED QUAY W ALL ....................................................................................... 99 10.2.1.2. OPEN QUAY STRUCTURES .............................................................................. 103 10.2.2. Scour due to Main Propeller ................................................................................. 107 10.3. DESIGN OF BOTTOM PROTECTION ................................................................................. 107 10.4. DESIGN OF M ATTRESSES OR CONCRETE SLABS ............................................................. 112 10.5. EXTENT OF THE PROTECTION........................................................................................ 113 10.6. REPAIR OR UPGRADING OF EXISTING BERTHS ................................................................ 115 10.7. OPERATIONAL GUIDELINES ............................................................................................ 119 Design Guidelines And Recommendations .......................................................................... 121 11.1. DESIGN GUIDELINES AND RECOMMENDATIONS ................................................................ 121 11.2. GENERAL RECOMMENDATIONS ...................................................................................... 123 References ......................................................................................................................... 124

ANNEXES  ANNEX A. DEFINITIONS AND SYMBOLS .................................................................. A-3  ANNEX B. DIMENSIONS OF SHIPS ........................................................................... B-5  ANNEX C. DAMAGES – QUESTIONNAIRE ..............................................................C-17 C.1 PORTS P ARTICIPATING TO THE SURVEY............................................................................C-17 C.2 SUMMARY OF THE ANSWERS ...........................................................................................C-18 C.2.1. Situation ........................................................................................C-18 C.2.2. Monitoring/Studies .........................................................................C-19 C.2.3. Protective Measures ......................................................................C-19 C.2.4. Other .............................................................................................C-20

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1. FOREWORD &TERMS OF REFERENCE 1.1.

Foreword

Marine transport is constantly undergoing development in order to comply with the ever-changing demands of the international market. During the last decade the developments in the shipping industry have primarily been characterised by an increase in capacity. Ships are becoming larger and deeper with higher freight capacity. This has an effect on the harbour infrastructure: basins have to be deepened, quay walls strengthened and approach channels widened. Container terminals are being designed and constructed to accommodate 18,000 TEU vessels and Ultra Large Container Ships up to 23-25,000 TEU are designed, cruise ships are under construction to accommodate more than 8,000 persons and fast ferries reach higher speed and larger size [Hansa, 2008]. As a result of this growing size we see an increased power of modern ships. Larger and more powerful propellers cause higher flow velocities and thus more damage to existing harbour bottoms which require bottom protection.  An additional development aggravating this problem is that modern ships have increased manoeuvrability: they not only possess main propellers at the rear of the ship but also bow and stern thrusters. These secondary propulsion systems allow the ship to manoeuvre independently, without tugboat assistance during berthing and de-berthing. Large ships, such as ferries, use their propellers to manoeuvre in harbours. The function of the main propeller at the rear of the ship is predominantly for forward thrust, but can aid a manoeuvre by changing the direction of the rudders. Stern thrusters are found at the back of the ship in a duct perpendicular to the axis of the ship. Nowadays, the classic forces of a main propeller and a stern thruster can be combined by a rotatable thruster, such as an azipod or a hydrojet. Bow thrusters are similar to stern thrusters but are situated at the front of the ship. As a result of the increase in size and engine power of the thrusters, the flow velocities against the quay walls and at the harbour basin bottom in front of the quay walls have increased considerably over the last few years. Because the harbour bottoms are often not designed for these extreme velocities, this can lead to an increased bottom erosion and possibly to quay wall failure. This bottom erosion can be minimised by placing a well dimensioned harbour bottom protection. The awareness of the damage to existing harbour infrastructure and the concern to properly design future harbour facilities form the basis of PIANC’s decision to prepare new guid elines for the design of berthing structures, related to modern propulsion systems. Insight into vessel propulsion induced flow and the resulting damage or required strength of the protection is mandatory to take appropriate costeffective measures to protect harbour structures. 1.2.

Terms of Reference

Background

The objectives of the MarCom Working Group 48 have been defined in the Terms of Reference, drafted by the Maritime Navigation Committee (MarCom) and validated by the PIANC Executive Committee (ExCom). The former report of PIANC Working Group 22  – ‘Guidelines for the Design of Armoured Slop es under Open Piled Quay Walls ’ (1997) gives practical guidance but only for the design of rock scour protection. This new report, PIANC WG 180, takes precedence over the previous WG 22 report, but the earlier report still contains useful information and can be used where appropriate. However, the increase in scour actions of modern day vessels is often beyond the practical limits of performance for rock protection. Mattresses and other types of scour protection will be outlined and their design 1

methods are under development. A more accurate method is also presented for the determination of the size of rock on slopes under attack of propeller induced currents: problems have been encountered with the PIANC WG 22 design guidelines for armoured slopes under attack of thrusters because of the increased use and power of those thrusters. Although especially large and fast vessels cause problems related to slope protection, problems have also been reported with relatively small vessels when thrusters have been used. Stability of riprap has become relevant and a more accurate method is needed to protect port structures, especially armoured slopes, cost effectively against transverse thruster induced currents. As such these new PIANC guidelines (MarCom WG 180) takes precedence over the previous PIANC WG 22 report [PIANC, 1997] but that earlier report still contains useful information and can be used where appropriate. Terms to be Investigated, Amended by the Working Group for approval by MarCom

The report should cover the following subjects: 1) Noticed damage at port structures under attack of propulsion actions (propellers, thrusters, water jets) and the related information about ships, protections and structure type (a questionnaire to the port authorities, etc.)

2) Identification of the problem 3) Velocity fields caused by different types of propulsors (also possible contacts with the manufacturers of these equipments) 4) Scour in front of and around berthing structures, damage locations and stability risks of the berthing structures 5) Damage to structural material (including the effect of ice) 6) Design philosophy for new berths and for repairing and upgrading existing structures (to accommodate larger vessels), with attention to ‘bottom protection ’ and ‘scour allowance ’ The final title of these guidelines has been proposed by PIANC ExCom in May 2014: ‘Guidelines for Protecting Berthing Structures from Scour Caused by Ships ’.

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2. MEMBERS OF PIANC MARCOM WG 48 2.1.

Members

Chairman: Mr Marc SAS Manager Int. Marine & Dredging Consultants (IMDC). Coveliersstraat 15 B-2600 Antwerp Belgium Phone: +32 3 270 92 95 Fax: +32 3 235 67 11 E-mail : [email protected]

Co-Chairman: Mr Henk VERHEIJ Deltares & Delft University of Technology Postbus 177 2600 MH Delft The Netherlands Phone: +31 88 335 8137 Fax: +31 88 335 8582 E-mail:[email protected] E-mail: [email protected]

Mr C.A. THORESEN Haskollvegen 33 N-3400 Lier Norway Phone: +47 32 84 60 95 Mobile: +47 950 54 848 E-mail: [email protected]

Mr José Luis ZATARAÍN Infrastructure Director Santander Port Authority Carlos Haya 23 39009 Santander Spain Phone : +34 942 20 36 05 Fax : +34 942 20 36 32 E-mail:[email protected]

Mr Marcel HERMANS Port of Portland PO Box 3529 7200 NE Airport Way Portland, OR 97218 USA Phone: +1.503 415-6305 Fax: +1.503 548-5992 E-mail: [email protected]

Mr Graham HORNER BA MICE MHKIE Horner Consulting Services Kennett House Kennett Lane Stanford KENT TN25 6DG Phone: +44 1303 812320 Mobile: +44 7810871720 E-mail: [email protected]

Dr. Eckard SCHMIDT WKC Hamburg GmbH Tempowerkring 1b D.21079 Hamburg Germany Phone: +49 40 790001532 E-mail: [email protected]

 Alternate member: Ir. Dirk POPPE, Ing. Jelle VAN BOGAERT DEME Scheldedijk 30 2070 Zwijndrecht Belgium Phone: +32 3 250 57.82 Fax: +32 3 250 52.53 E-mail: [email protected] [email protected]

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2.2.

Corresponding Members

Mr S.M. KULKARNI Chief manager Jawaharlal Nehru Port Trust  Administration Building Sheva, Navi Mumbai 400707 India Phone:+ 91 022 27242292 Fax: +91 022 2724150 E-mail: [email protected] [email protected]

Prof. PhD Eng R. CIORTAN Deputy General Manager IPTANA – SA Blv. Dinicu Golescu 38 Sector 1 Bucharest Romania Mobile Phone: +40 744 3000 53 Fax : +40 21 312 14 16 E-mail: [email protected]

Dr. Christoph MILLER Previously Head of Port Construction, HPA 3-1 HPA Hamburg Port Authority Neuer Wandrahm 4; 20457 Hamburg Germany E-mail: [email protected]

Dr. J. G. de GIJT Senior Consultant Municipality of Rotterdam Stadsontwikkeling Ingenieursbureau  Ass. Prof. at Delft University of Technology, Hydraulic Engineering Section Phone: +31 65 1612862 E-mail: [email protected]

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2.3.

Meetings

The Working Group started its activities in Brussels in May 2004. A number of meetings were held in London, Madrid, Oslo, Amsterdam and Brussels until the end of 2007. From then on, numerous meetings with a limited group of members were held in Hamburg, Delft and  Antwerp. 2.4.

Acknowledgement

The preparation of this report was not possible without the input and critical review of external experts, e.g.      

Prof. Dr. Klaus Römisch, Germany Bernhard Söhngen and Detlef Spiter, Federal Waterways Engineering and Research Institute, Karlsruhe, Germany Prof. Jochen Aberle, Department of Hydraulic and Environmental Engineering, Norwegian University of Science and Technology, NTNU, Trondheim, Norway Prof. Dr. Ir. Marc Vantorre, University of Ghent, Belgium Ir. Teus Blokland, Municipality of Rotterdam, Engineering Department, The Netherlands Martin Hawkswood, Proserve, and Peter Hunter, HR Wallingford, UK

Special thanks goes to the staff of IMDC in supporting the editorial work, especially to Sarah Audenaert, Lesley Frederickx, Hannan Abrddane and Luuc Asselbergs. Thanks also to the staff of PIANC Headquarters in Brussels for final formatting and publishing this document.

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3. INTRODUCTION 3.1.

Aim of the Report

The aim of the report is to provide practical guidelines and detailed background inf ormation about vessel propulsion in order to allow the designer to make a proper design of a quay wall structure and the bed in front of it. This design can be based on the philosophy to allow scour or on the design philosophy to protect the quay wall against erosion by using a rip rap protection or mattresses. The design guidelines as proposed in this document consist of a framework to determine the efflux velocity from propulsors, the velocity distribution in the jet and the velocity at the bottom. Based on these loads a coherent design philosophy is presented for a riprap protection based on standard guidelines such as BAW, EAU and the Rock Manual as well as for mattresses for which such coherent guidelines were lacking at present but are developing [Raes et al., 1996 ; Hawkswood, 2013]. The report deals in particular with very high velocities often caused by propellers, podded propulsors or water jets. It should be noted that the report does not cover the flow field created by contra rotating propellers.  Although the quay structures could be vulnerable to abrasive action from thruster currents in situations with sandy bottom material or floating ice, this aspect is not dealt with in this report. The selection of a particular berthing structure is in general not based on its performance with respect to scour, hence no recommendations regarding this selection are formulated in this report. 3.2.

Structure of the Report

Following the introductory Chapters 1 to 3, Chapter  4 gives an overview of typical quay wall structures in relation to the effects of the thrusters. Chapter  5 describes different types of propellers and water jets and Chapter  6 gives an overview of berthing and departure procedures. Chapter 7 briefly deals with failure mechanisms and Chapter 8 describes the velocity distribution in a  jet. Both the general equations as a number of specific cases are provided. Materials, suitable for bottom and slope protection are described in Chapter  9. Finally, Chapter  10 gives a design philosophy and Chapter  11 gives design guidelines and recommendations. 3.3.

Related Documents

The topic of propeller and thruster induced velocities and their interaction with berthing structures (and more generally maritime infrastructure) has been described in a number of PIANC documents: PIANC Guidelines 





PIANC Working Group 22 – ‘Guidelines for the Design of A rmoured Slopes under Open Piled Quay Walls’ (1997): this document gives a practical method for determination of the size of rock on slopes under attack by propeller induced currents. As stated previously, this guideline remains in force unless superseded by the PIANC WG (48) 180 guideline. PIANC InCom Working Group 27 – ‘Consideratio ns to Reduce Environmental Impacts of Vessels ’ (2008), Report 99: this document gives an overview of propulsion systems (focussed on inland navigation) and on methods to determine propeller related scouring. PIANC MarCom Working Group 31  – ‘Life Cycle Management of Port Structures  –  General Principles ’, PTC 2 report of WG 31 – 1998.

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    

PIANC Working Group 34 – ‘Seismic Design Guidelines for Port Structures ‘ (2001). PIANC MarCom Working Group 41  – ‘Guidelines for Managing Wake W ash from High-Speed Vessels’ (2003). PIANC MarCom Working Group 1211 (2014) – ‘Harbour Approach Channels Design Guidelines ’. PIANC MarCom Working Group 1601  (to be published)  – ‘General Principles for the Design of Maritime Structures’. PIANC MarCom Working Group 56 (to be published)  –  ‘Application of Geotextiles in Waterfront Protection ’.

PIANC Bulletin/E-Magazine

Numerous papers have been published by PIANC regarding problems related to propellers, jets and erosion. The reader is referred to the reference list. Standards and Guidelines

No standards have been identified dealing with the design of berthing structures related to propulsion systems, although some standards of related topics exist. For example, those dealing with issues with regard to armour stone and other material, including concrete armour units. Nevertheless, a number of general Reference Books are considered to give the reader guidance on current good practice for the design of berthing structures:      

BAW (2005): “Principles for the Design of Bank and Bottom Protection for Inland Waterways ”, Mitteilungen 88, Federal Waterways Engineering and Research Institute, Karlsruhe. CIRIA, CUR, CETMEF (2007): “Rock Manual, The use of rock in hydraulic engineering (2 nd edition)”, C683, CIRIA, London. CUR (2005): “Handbook Quay Walls, CUR 211E ”, Taylor and Francis Group. EAU (2009): “Recommendations of the Committee for Waterfront Structures  –  Harbours and Waterways ”, Digitised and updated edition. U. S. Army Corps of Engineers: “Coastal Engineering Manual ”. ROM (2000): “Recommendations for Maritime works ”, Ministry of Public Works, Spain.

The Rock Manual should be used with caution, as it omits the effect the rudder has increasing bed scour velocities. 3.4.

Definitions and Symbols

 A complete list of symbols and definitions is given in ANNEX A. The figures on the next page (Figure 3.1 and Figure 3.2) illustrate the physical system and the general characteristics of propeller and thruster induced velocities in relation to berthing structures.

1 New

WG number

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Figure 3.1: Container vessel moored alongside a quay wall with a protected bottom

Figure 3.2: Flow field induced by a bow thruster

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4. QUAY STRUCTURES 4.1.

Introduction

This chapter discusses the general background of berth structures and in particular describes design aspects of berth structures in relation to propulsion actions and scour impact. This report distinguishes between two principal types of quay structures:  A) Solid Berth Structures:  Sheet pile structures  Gravity structures B) Open Berth Structures The scour problem related to Solid Berth Structures (Type A) is limited to erosion of the bed material in front of the structure, whereas scour related to Open Berth Structures (Type B) is more complex and can include:  

scour around the piles in particular those near the berthing face scour of the slope underneath the quay, even up to the top

Scour impact from propulsion actions to both these types of berth structures will be described in Chapter 7  – ‘Damage and Failure Mechanisms ’ of this report. The most severe erosion impact on slopes underneath the berth or on the sea bottom can commonly be both from the main propeller or from transverse thrusters. Container vessels, Ro/Ro vessels and ferries are known to be major contributors to erosion near berths. Specific information on all propulsion systems is included in Chapter  5.  Although scour can occur near berth structures due to natural currents, they are specifically vulnerable to scour caused by vessels’  propeller action. Especially during berthing and un-berthing, eroding forces on the seabed in front of the berth or on the slope underneath the berth can be substantial. The action of the vessels’ propeller is a main eroding factor due to the resulting current velocities which can reach up to 8 m/s near the bottom compared to for example the tidal current, which is t ypically limited to around 1 or 2 m/s. The propeller currents are due to:   

The main or stern propeller (or ‘ screw’) which will cause an induced jet current directly behind the propeller, directed by the rudder The transverse thrusters with a propeller, which is located crosswise to the longitudinal axis of the ship, which are most commonly located at the bow and occasionally at the stern

Impacts such as bottom erosion from the ships’ main propeller depend on many factors which may be different in almost every situation. Typically for design purposes, the governing condition occurs when the propeller is closest to the bottom so when the vessel is loaded and when the tide is at its lowest. Use of the ships ’ main engine and propeller may be quite different in berthing and un-berthing operations. Those in turn may depend on factors like: use of the berth, the cargo streams, the local physical situation as it relates to tide, current and wind as well as local customs, regulations, availability of tugboats, etc. Berth structures should be designed and constructed to safely resist the vertical loads caused by live loads, trucks, cranes, etc., as well as the horizontal loads from ship impacts, wind, fill behind the struc ture, etc. 9

It is not within the scope of this report to provide design guidelines for the choice of a berth type in general. While every designer should determine the technically and economically preferred berth t ype for their specific situation at hand, this report and chapter gives specific considerations for berth design as it relates to thruster impacts. 4.2.

Categories of Berth Structures Relevant to Propulsion Actions

There are many different berth structures in use throughout the world. Some of the main design factors for berth structures are the local site conditions such as geotechnical conditions, water levels, currents, availability of materials, etc. and the characteristics of the design vessels for the quay (draft, length, DWT, propulsion system, etc.). This chapter discusses berth structures in relation with the use of propulsion systems by the vessels using the berths. In this report, berth structures are characterised according to their relevance to the impact of propulsion systems. For that purpose, the different berth structures are reduced to two main categories, namely Solid Berth Structures (4.2.1) and Open Berth Structures (4.2.2) as addressed below. 4.2.1. Solid Berth Structures

For this type of berth structure, the land surface or fill is extended right out to the berth front where a vertical front wall is constructed in order to resist the horizontal load from the fill and any live loads on the apron. Solid berth structures can be subdivided into the following two main groups, depending on the principle on which the front wall of the structure is constructed in order to obtain suff icient stability: 1.

Gravity Wall Structure (including cellular sheet-pile structures). Gravity structures are based on

the concept that the weight of the structure itself provides the resistance against forces that could result in movement such as sliding or tipping. The structure with its own dead weight and bottom friction provides the resisting force to any loads from backfill, live load and other horizontal and vertical loads acting on the berth wall structure itself. The weight resisting movement of the structure can be provided either mainly by the structure itself (Figure 4.1 and Figure 4.2) or by a combination of the structure and its fill (Figure 4.3 and Figure 4.4) The following figures are examples of different types of gravity structures:

Figure 4.1: Massive monolithic structure  – soil retaining structure consisting of an monolithic concrete core with foundation on rubble

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Figure 4.2: Block wall structure  – soil retaining structure consisting of several concrete core elements with foundation on rubble

Figure 4.3: Caisson – soil retaining structure consisting of an open concrete body filled with sand or rock and with foundation on rubble.

Figure 4.4: Cantilever monolithic structure – soil retaining structure consisting of an open concrete body filled with sand or stones and with foundation on rubble.

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Figure 4.5: Cellular sheet pile structure  – soil retaining structure consisting linked cells of sheet piles (filled with sand or rock)

2. Sheet Pile Wall Structure. Sheet pile walls may be simple cantilevers in which case scour of the passive wedge will have a significant effect on the stability. If the front wall by itself is not adequate to resist the horizontal loads acting on the structure it must be anchored to an anchoring plate, wall or rock behind the berth. This category includes steel sheet piles and concrete structures, such as diaphragm walls. The common factor of sheet-pile structures is that they retain the soil behind the structure by a vertical sheet-pile wall which is also normally the face of the berth. Vertical loads are either transferred directly onto the soil (Figure 4.6 and Figure 4.7) or through a relieving platform (Figure 4.8). Horizontal loads are transferred either by the cantilever wall structure itself (Figure 4.6), by an anchoring system with additional (battered) piles (Figure 4.7 and Figure 4.8) or by an anchor wall or a friction slab system behind the wall.

Figure 4.6: Cantilevered sheet-pile retaining structure

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Figure 4.7: Anchored sheet-pile retaining structure

Figure 4.8: Sheet-pile with platform

Solid berth structures are in general more resistant to impacts than open berth structures, i.e. the resistance to impact from vessels decreases with increasing slenderness of the structure. For instance, a block wall wharf is far less vulnerable than a pier built as an open berth on piles. The applied loads on solid berth structures are typically a smaller portion of the overall loads acting on the structure than for open structures so they can be more tolerant to exceptional live loads. On the other hand, the safety factor applied for solid berth structures is normally lower than for open berth structures. 4.2.2. Open Berth Structures

For this type of berth structure, a load bearing slab supported by piles, columns or lamellar walls is constructed, stretching from the top of a dredged, filled or natural slope to the berth front. Open berth structures typically have a clear separation between how they transfer horizontal and vertical loads. Vertical loads are transferred from the platform directly to the structural piles or foundation. Horizontal loads are transferred either by the deck and its anchoring (Figure 4.9), by battered piles placed under an angle (Figure 4.10), by a friction slab behind the wall or by a combination of the three (Figure 4.11). Typically, the soil resisting vertical loads are some distance below the surfaces vulnerable to scour, but revetted slopes and piles(resisting horizontal loads in bending) are potentially at risk in the case of scour. 13

Figure 4.9: Pile/column supported deck

Figure 4.10: Pile supported pier with battered piles

Figure 4.11: Pile/column supported deck with anchoring through a friction slab

Due to access difficulties under an open berth after the completion of the deck structure, investing in a maintenance-free approach is usually appropriate and cost-effective from a life-cycle perspective for the design of slope protections underneath an open berth structure.

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4.2.3. Hybrid Structures

It is noticed that the structures are subdivided into categories related to their response on thruster impact. From a purely structural perspective, some structures are better fit in another category than the one they belong to now. Regardless, readers are cautioned against focusing solely on one category in their analysis, especially in the case of structures that are sort of a hybrid. The Cellular Sheet-pile Structure (Figure 4.5) behaves like a gravity structure, but also has similarities to the sheet pile type (Figure 4.6, Figure 4.7 and Figure 4.8) as it makes use of passive resistance of the seabed meaning that the structure may be at risk of leakage of filling material. Also depending on the method of soil retaining behind the structure, thruster issues of certain pile supported deck structures (Figure 4.11) are very similar and related to those of the category Sheet-Pile Structures. 4.2.4. Other Berth Types or Structures

In the situation where a floating barge is used as a floating dock structure (because of big tidal variations or for other reasons) to offload vehicles or other cargo, erosion problems due to thruster scour could occur to the supporting or anchoring system. The dock itself floats and moves up and down with the water level but it is often secured in place horizontally by pilings/mooring dolphins. Relevant scour issues can be scouring around those mooring piles (similar to the situation of pile supported structures) or issues related to deposits of the scour action that could cause problems during low water for draft of the floating dock itself (due to sediments that may be blown underneath the floating dock by thrusters and as a result cause grounding of the barge/dock). This is of particular importance for Ro/Ro stern ramps where the bed is directly exposed to current and flow from the main propulsion system of the vessels. 4.2.5. Modified Structures

Berth structures as described above are the base concepts where the majority of existing berth structures can be categorised in. However, there are also many berth structures that have been substantially modified in response to changing circumstances or requirements. The growth experienced in vessel sizes over the last several decades has led to many existing structures being modified to accommodate greater depths, stronger thrusters, etc.  A very common method of upgrading the depth of an existing berth structure is by building a new berth structure in front of it. In many cases, this new structure will be close enough so that it will interact with the old structure and structurally they will need to be analysed as one joined berth system. In most cases, thruster impacts will be fully governed by the new structure in the front. However, in some cases the thruster/scour analysis will need to incorporate the old structure behind it. Some examples of modified structures are illustrated below.

Figure 4.12: Gravity structure with deeper sheet pile wall in front

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Figure 4.13: Gravity structure with deeper grout piles

Figure 4.14: Open pile structure with underwater sheet pile wall at the toe

 Another situation of modified structures is where an existing dock or pier has been extended because more dock front length was needed over time. This dock extension could either be of the exact same type and characteristics as the existing structure or more likely since many years will have gone by since the initial dock was constructed, the dock extension will reflect and incorporate new insights in design and development and the extension will differ from the initial berth structure. Both cases will be addressed in paragraph 4.6 below. More illustrations of modified structures are given in paragraph  10.6. 4.2.6. Future Developments 4.2.6.1.

Introduction

Over the last hundred years a considerable change in shipping has occurred. Especially in the last decades, container shipping has changed considerably. Also the handling of commodities on the terminal is still open to further logistic optimisation. This chapter discusses possible future changes in functional and technical requirements: factors like development of ships, the cargo handling facilities, storage facilities and logistical changes are highlighted. All these factors must be balanced during the design stage because they may influence the possible benefits as well as the costs of investment, maintenance and future upgrading. Rethinking about the design of quay walls might be beneficial. This might mean that the optimal is not just building a quay wall, rigid and everlasting, like in the old fashioned way [De Gijt, 2010 ; CUR, 2005]. 16

4.2.6.2.

Trends Which Influence the Design of Quay Walls

 A quay wall is a vertical boundary between water and land which facilitates cargo handling with cranes directly from ship to terminal. In the past, unloading occurred via smaller boats from the upstream ship to the shore. However, this became too time consuming and quays were built to improve the cargo handling logistics. So future trends in quay wall design mostly come from outside the quay wall structure. Considering trends that influence the design of quay walls the following list can be composed:         

Changes in producer and consumer markets Logistic concepts Port layout Ship development Cargo handling facilities Boundary conditions Quay design methods Construction materials and techniques LCM & maintenance concepts

4.2.6.3.

Rethinking Economical, Design and Usage Life Time

Today it is common practice to design a quay wall structure according the available design codes for a life time 50 years or more. However, the time over which a quay wall is used for the same purpose is rather limited (Figure 4.15), meaning that such a rigid design is possibly not the most cost effective solution.

Figure 4.15: Service life in relation to time of construction (de Gijt personal comment 2002)

Furthermore, port authorities estimate the economic lifetime in relation with the contract negotiations with their clients. This economic lifetime is not necessarily the same as the technical or usage lifetime. Theoretically, one might anticipate that if the economic-, usage- and technical lifetime are equal the most optimal solution is obtained. However, the time of uniform use is more and more uncertain. Therefore, some extra investmen ts in a more flexible and thus ‘ future proof ’ structure may result in a second or even third economic lifetime.

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4.2.6.4.

Cargo Handling Development

Today existing ore cargo handling equipment with immense cranes up to lifting loads of 60 tonnes has probably reached its limit. This is completely different from the container vessel loading and unloading facilities because container ships might increase in dimensions, especially in width and draught and thus in capacity. This implies that the container cranes need more capacity and not just a greater outreach. A solution in another direction might be (un)loading on two sides by floating cranes or complete double sided terminals (Figure 4.16). This situation is comparable with manoeuvring in a lock. The impact of the jet of bow thrusters should be considered carefully.  A total different solution are floating terminals (Figure 4.17). The pictured structures are flexible so they can be moved to another location.

Figure 4.16: (Un)loading on two sides by a complete double sided terminal [CUR, 2005]

Figure 4.17: Floating structures [de Gijt, 1998]

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Examples of possible future designs: new possibilities for future quay wall st ructures are synthetic constructions.

Figure 4.18: Synthetic quay wall [de Gijt, 2010]

In Figure In Figure 4.18 a synthetic block structure is presented. This structure consists of synthetic blocks filled up with sand. In fact it is a gravity type of structure which is due to its composition flexible and removable.

Figure 4.19: Ocean brick quay wall [CUR, 2005]

The quay wall in Figure 4.19 consists of concrete blocks in which the concrete is reduced to the minimum which is necessary for structural requirements. The blocks can be stapled depending on the required height of the structure.

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Figure 4.20: Quay wall structure with screw injection anchors

The concept of a quay wall structure with screw injection anchors has been developed to cope with deepening of the nautical depth in the future. The quay wall consists of concrete blocks which are connected with screw injection anchors to the subsoil. It is required that a good sand layer is present. The advantage is that the retaining height can be increased in the same vertical and thus not influencing the width of the harbour basin. 24.0m  Isolation mantle  +4.00  N.A.P.

    m      0  .      7      2

Frozen soil 

Contract depth -19.65  Bottom depth -20.65 

Construction depth -23.00 

Figure 4.21: Frozen quay wall 

Recently, a preliminary study has been performed regarding the use of a frozen quay wall. This concept is flexible and removable and it seems viable when the usage time is approximately 10 to 15 years. Nevertheless, Nevertheless, these new quay structures do not result in another view regarding design of bottom protections and scour.

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4.3.

Material Types of Berth Structures

The most common material types used for berth structures are steel (for piles and sheet pile walls), wood (timber piles and decks) and concrete (gravity structures and decks), although some other materials are used in rare cases as well (e.g. stone for gravity structures). Occasionally, the type of material of the berthing structure is relevant regarding the impact from propulsion systems or vice versa. It is recommended to evaluate during the design whether this may be the case in that individual situation. For example, steel piles usually require protective coating which could be vulnerable to abrasive action from jet currents in situations with sandy bottom material or floating ice. 4.4. Soil and Geotechnical Aspects Relevant to Berth Structures and Vessel Propulsion Systems

One of the main determining factors for f or the structural design of a berth structure is the local geotechnical geotechni cal situation. As soft soils are less suitable for the application of gravity type structures (Figure 4.1 to Figure 4.5) environments with soft soils are more likely to see berths of sheet-pile and pile supported structures (Figure 4.6 to Figure 4.11). The local soil conditions do not only affect the geotechnical site conditions, but are also directly related to the scour potential of the bottom material at the berth. For example, although from a structural perspective ‘gravity structure ’  generally just refers to a solid face structure on a foundation that is typically shallow, it also indirectly implies that the subsurface soil type is likely not soft or fine grained. In this report, the approach is to address scour issues and forces exerted on bottom materials at the berth, based on vessel type and berth structure type. The fact that in many cases the design or the selection of the berth type has been made  – in part – based on the soil characteristics at that berth is relevant but not for the way or order these scour issues will be addressed in this report. 4.5.

Vessel Types Relevant to Berth Structures and Propulsion Actions

Transverse thruster availability, characteristics and use vary largely by vessel type. While bow thrusters are standard equipment on cruise, car and container vessels, they are less common equipment on bulk carriers. A more detailed overview of the different types of thrusters is given in Chapter 5. Typically, Typically, berth structures are designed for a certain design vessel or at least for a certain vessel type. Since different vessel types can have very different bow thruster characteristics (such as percentage of vessels in that vessel category or class that are equipped with bow thrusters, their size, power, current velocity, etc.) there is also an implicit relationship between type of berth structure and thruster use at that berth. A solid berth structure for example, will have very different diff erent design requirements requirements for thruster t hruster impacts impacts if the intended use of the berth will be primarily by cruise ships as opposed to by bulk carriers.  As part part of the design design process process,, an assessm assessment ent will will need to be made made whether whether there there is sufficien sufficientt information and long-term certainty about vesse l use at the berth, or whether it’s appropriate to ‘overdesign’ in order to have more flexibility regarding future types of vessels using the berth. The designer should also consider the option of designing for the current fleet but with an arrangement so that the structure can be modified in an economical way for more severe conditions should new vessels be introduced. In this context it can also be noted that the existence of quay features such as stern ramps and loading machinery in relatively fixed positions may limit the area over which the structures are subjected to the severest conditions. The designer must then take care that all possible present and future uses of the berths are considered before providing different levels of protection in different parts of the structure. Consider, for example, a berth for a drive-through

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Ro-Ro service where vessels normally berth stern-in but may have to berth bow-in in special circumstances. 4.6.

Specific Elements of Berth Structures Relevant to Propulsion Actions

 As with all structures, special attention should be given to transition points, edges, corners and similar elements of berth structures. These are truly special elements of berth structures where both the load and the way the structure handles or responds to the load can be quite different than for the rest of the structure. In all cases, these special elements should be analysed separately for propulsion actions to determine whether the structure is sufficiently protected against that load in that specific situation. In some cases, the berth structure itself may not require special design for the propulsor actions, but a specific element (such as a corner or transition) may. 4.6.1. Corners

For solid face berth structures (Figure 4.1 till Figure 4.5 and Figure 4.6 till Figure 4.8) the corner or edge of the berth structure will in many cases somehow connect to or transfer into a slope. Depending on the specific situation, such a slope may either extend as the regular bank parallel to the berth structure or may have a slope that connects perpendicular to the berth structure. For pile supported structures (Figure 4.9 till Figure 4.11) the corner or edge of the berth structure will in many cases be a continuation of the slope that is present underneath the deck, or in some cases that slope may curve around to become perpendicular to the structure.

Figure 4.22: Corner situation with bow thruster jet flow parallel to slope

For slopes that are perpendicular to the berth structure, one needs to be careful that the typical transverse thruster load – if applicable in that spot – will be parallel to the slope and not pushing up the slope as it does underneath a pile supported deck. This may result in different requirements for slope protection. 4.6.2. Transition Between One Structure Type and Another

When different berth structures are built adjacent to each other the zone between the two structures will be a transition. In many cases, the distance between the two will be in such a way that the transition will be regular bank and the edges of each structure can be considered a corner as described above. In that case, corners and bank in between will need to be designed accordingly.

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In some cases, one structure type will immediately border and transition into another structure type. For example, a pile supported deck can border a gravity structure of some sort. 4.6.3. Transition in One of the Main Structure Characteristics

In some situations, the type of two bordering berth structures may be the same, but there might be a significant difference in one or more of the main characteristics, for example the depth in front of the structure. The berth length of an existing caisson or cellular sheet-pile structure may need to be extended, while the new situation calls for a greater depth at the new portion of the berth structure. In that case, a transition slope between the different depths will be needed at the bottom, which leads to a special configuration that may need special attention during design. 4.6.4. Berth Pockets and Other Irregularities

Depending on the situation and type of structure, there may be special features or certain irregularities at the berth structure that could cause an impact on scour or thruster use at the berth structure, or that could vice versa be impacted by thruster use. Examples are:    

fender system (for illustration see Figure 4.23) ladders outfalls/drainage features

These could be relevant both because they could impact (direct, divert, concentrate, etc.) currents from transverse thrusters and also be subjected themselves to the concentrated current from transverse thrusters. In some cases water intakes or outlets or even measuring instruments such as automatic tide gauges might be situated at a berth that may be subject to propulsion action impacts, and may need special protection.

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Figure 4.23: Quay wall with fender piles (Altenwerder Container Terminal Hamburg ) [Miller, 2008]

Berth pockets are used in harbours with significant tidal water level variations where vessels enter and depart during tidal windows, so that deep drafted vessels can stay along the berth during low tide. During the design process of such berth pockets, the underkeel clearance should be selected carefully. The underkeel clearance during manoeuvring may be more than the minimum required while at berth. In situations where berth pockets are used, the impacts of thrusters is likely to extend to lower elevations of the berth structure. This aspect will have to be taken into account in analysing and designing the structure. Depending on the depth of the berth pocket below grade, the transition slopes to the regular bottom elevation may also need to be a specific item of attention.

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5. PROPULSION SYTEMS 5.1.

Overview of Different Types

This section gives an overview of the different types of devices driven by an engine and used in a ship to provide the necessary thrust to navigate or to manoeuvre. Next a description will be given of the different classes of propulsors used in navigation, independent of the type of engine or source of energy used. The most typical and frequent used ship propulsion system is a propeller. It employs a shaft more or less parallel to the centre line that provides the rotational movement to the central hub of the propeller.  Around the hub there are several blades, symmetrically arranged, turning on a vertical plane. These are three-dimensional blades with a cross section like a wing profile to avoid cavitation and to provide the forward needed thrust in accordance with the Bernoulli theorem when rotating. As in the case of airplanes, the blades attack the water with an angle known as pitch. The front side of the blade is longer and consequently there is less hydrodynamic pressure than that at the back side resulting in a forward thrust. The propeller needs to have a symmetrical distribution of mass in order to avoid vibrations. Depending on the angle between the blade chord line and the plane of rotation a detachment of the laminar boundary layer could appear which could produce pressure below water vapour pressure (cavitation), so each propeller and each blade pitch and cross profile must be designed for the appropriate standard regime with less performance at other speeds.  A propeller is characterised by the number of blades (4 or 5 usually), the external diameter, the angle of the blades according to the pitch, the power and thrust delivered at standard regime, the speed and also by the direction of rotation, according to the way it turns looking from aft to bow. When a ship has only one propeller, it normally rotates in a ‘clockwise ’ direction. Because of the distance between the centres of the blades in both positions, a moment appears. It also causes the ship to have some roll and a tendency to turn more easily to one side. When a ship has two propellers, the starboard one rotates clockwise and the port side one rotates counter clockwise in order to compensate the tangential thrusts. So in their upper position, the blades can be seen turning towards the sides of the ship. The number of blades is related to their area and to several propeller-shaft characteristics. The whole system, engine, gear, shaft and propeller should be designed to avoid transverse vibrations in the regime range. Further details of propulsion systems and principles can be found in literature, such as Bertram (1999), Brix (1993) and Rowe (2000).  An overview of azimuth thrusters and azimuthal podded drives (podded propulsors) and their suppliers is given in Hansa (2013a) and Hansa (2013b). Furthermore, it has to be noticed that propellers are classified into 2 groups: Wageningen B- and Kseries, in which the former is non-ducted and the K-series (stands for Kaplan series) is ducted [van Manen, 1956]. 5.2.

Types of Propellers

5.2.1. Fixed Pitch Propeller (FPP)

The first type of propeller used after the paddle wheels is the fixed pitch propeller. The blades are fixed to the hub and always have the same pitch. This type of propeller is usually applied for ocean-going vessels since it is the best choice in terms of efficiency, reliability and robustness because the propeller can be designed in perfect match with the ship’s hull and engine.

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Figure 5.1: Fixed pitch propeller: general view (left), Detail: Rolls Royce Propulsion (middle), Man B&W Diesel (right)

5.2.2. Controllable Pitch Propeller (CPP)

The angle of attack of the blades can be adjusted voluntarily from the bridge deck varying thus the pitch of the propeller. Although the cross section of the blade is asymmetric and it is designed to have the maximum performance at given pitch, forward speed and regime, this class of propeller provides very good output in other circumstances. Even when the ship moves backward by reversing the pitch to negative values. The main advantage is felt when the ship is manoeuvring in port or inland areas because it is possible to maintain the engine regime while reversing or cancelling the thrust, eliminating the need for reducing the engine regime before reversing it. Moreover, the engine can remain at its best regime doing careful manoeuvres by varying the pitch.

Figure 5.2: Controllable pitch propeller: general view (top left, Schottel), detail (top middle, Wartsila) (top right, Man Diesel),Installation on vessel (middle, Schottel) (bottom, Man Diesel)

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5.2.3. Contra Rotating Propeller (CRP)

The thruster has two in-line propellers turning in opposite directions, both pushing in the same direction at the same time whether forward or backward. The aft propeller makes use of the rotative energy left in the slipstream of the forward propeller when it turns in the opposite direction. The biggest advantage in this case is the lower propeller load, because the power is divided over two propellers.

Figure 5.3: Contra Rotating Propeller: general view of Contaz thrusters (left: Rolls Royce), detail (right: Volvo Penta IPS)

5.2.4. Ducted Propellers

The edges of the propeller blades are surrounded by a modified pipe in order to reduce the energy losses caused by centrifugal forces which drive the water outside the theoretical trajectory. The nozzle allows the propeller to push water more efficiently and equalizes the pressure at each blade point. The pipe is designed to smoothen the current lines at both edges of the cylinder. Its main use is when applied in low speed and high power manoeuvres, like in the case of tugs and auxiliary ships where the performance can rise 25 % above simple propeller cases. As with the types above, the ship needs a rudder to turn and change the direction of navigation. Nozzles give the propeller increased efficiency at low speeds, whilst they reduce the efficiency when the ship is moving at full speed. Nozzles are thus ideal for ships that need pulling power such as tugs, trawlers, etc.

Figure 5.4: 2 lips fixed pitch propellers with nozzles (Wartsila)

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5.2.5. Transverse Thruster

There is a variation of ducted propellers when tunnels are located through the hull providing transverse thrust. They are placed in a smooth tunnel near the bow in single or t win units in different frames taking in water from one side and expelling it out the other. They are very useful in turning manoeuvres allowing the pilot to do them without the help of tugs. This subtype is usually called bow thruster when located near the bow, or stern thruster at other positions (aft). Transverse thrusters lose their efficiency at sailing speeds above 2 knots. The power can reach 4 MW.

Figure 5.5: Tunnel Thruster (top left:Schottel),Scheme of tunnel Thruster (top right: Schottel), 4 transverse thrusters CT3500 (3.5 m diameter) on board Oasis of the Seas (bottom left and right: Wartsila)

5.2.6. Azimuthal Thruster 5.2.6.1.

Ducted Azimuthal Thrusters

 As an improvement to the ducted main propeller, the azimuthal thruster device can be turned by a vertical shaft, so the thrust can be directed in any horizontal direction, eliminating the need for a rudder. The shaft can be fixed to the hull or be retractable, even tilted to hide it inside the hull body. This type of propeller allows smooth changes in the direction of the required thrust changing from ahead to astern, even turning the ship around on its vertical axis without stopping the engine. Since the propeller shaft is horizontal and the device turns around a vertical axle, an intermediate gear box transmitting the rotation with an angle of 90º is used. This is called L coupling when used with electrical engines. When a Diesel engine is used and its shaft is horizontal, a Z coupling provides the additional 90º change of direction. The brand Schottel™ is one of the most representative for this type of thrust ers. The power can reach 6 MW.

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Figure 5.6: 2 Rudder propellers (top: Schottel), Installation on tugs (bottom: Schottel)

5.2.6.2.

Non-Ducted Azimuthal Thrusters

Obviously, also non-ducted azimuthal thrusters are in use. The advantages of azimuthal systems lie in the capacity of rotating the pods, providing 360º for manoeuvring purposes and ±35º in transit, increased propulsion system efficiency and power availability. Azi pod™ from ABB and Mermaid™ from Kamewa are the main representatives in the azimuthal systems group. The power can reach 25 MW.

Figure 5.7: 2 Rudder propellers (Schottel), Installation on tugs (Schottel)

5.2.6.3.

Double Non-Ducted Azimuthal Thrusters

In order to avoid the use of the rudder, two different thrusters can be installed on the same line, the forward one a controllable pitch propeller and the aft one a fixed pitch contra-rotating propeller mounted in a pod on the same centre line. The first propeller is powered by a shaft and the second one by means of an electric motor. Normally, the mechanical propeller has about 60 % and the pod about 40 % of the total installed propulsion power. Regarding the problems generated by thrusters, the capacity of these devices should be kept in mind for directing the thrust transverse to the banks or quays.

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Figure 5.8: General view of CRP Azipod (top: ABB), Installation on ULCV and ferry (bottom: ABB)

5.3.

Other Thruster Systems

5.3.1. Cycloidal Propeller

This device or group of devices transmits the thrust to the water by means of the hydrodynamic lift provided by several vertical blades rotating around a vertical axis placed under the hull. The shape of each blade is like the wing of a plane in a vertical position. When no thrust is required the chord line of each blade is tangent to the circle line which is described by the rotational movement of the blades around the common vertical axis. The bow and aft blades are conveniently rotated at a slight angle in such a way that the bow blade provides a ‘positive’ angle and the opposite one a ‘negative’ angle. As a result, the lifting effect of these two blades is added, providing a thrust and cancelling out their opposed friction forces. Intermediate positions of the other blades provide less thrust in the same direction. Thus, the blades combine their rotating movement around the main vertical axis with an oscillating movement around their own axis (cycloidal movement). The blade oscillation is provided in different ways resulting in a slight shift of a secondary vertical axis to the periphery of the circle line. There are two principal systems:

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Figure 5.9: Voith Schneider Cycloidal propellers (Voith Schneider)

a) Kirsten Boeing ™  produces the blades ’  oscillating movement around their own axis by means of an intermediate gear box placed between the main axis and the blade axis. b) Voith- Schneider™ produces the blades’ oscillating movement around their own axis by means of cranks and levers that act directly on the blade edge.

The captain only needs to shift a joystick in the same direction as the needed thrust. With the help of a power assisted circuit it is possible to apply more or less effect to the blades ’ angle of attack. This system of propulsion has less efficiency than that of the propeller but its disadvantage is compensated by its versatility in manoeuvring without varying the engine speed. Thus, it is possible to push forward and change instantly to stand by or backward. Combining two or more thrusters , the ship can move sideways or turn around its central axis without the need of a rudder. Consequently, this type of thruster is very suitable for tugs and auxiliary ships. The range of power can reach 4 MW. 5.3.2. Water Jets

Water jet propulsion is the most common propulsion system for high-speed vessels [Faltinsen, 2005].  A practical description of water jet propulsion can be found in Allison (1993). The ship has a flat hole at the bottom of the hull taking in sea water which passes through a nozzle where an axial pump driven at high speed by a horizontal shaft linked to the engine is located. The nozzle is designed for accelerating the flow. A considerable jet of water is impelled backwards through the aft pipe where two sets of pistons, acting on flaps or diverters, produce a jet deviation. One set of these diverters is partially or totally lowered achieving neutral or backward thrust, thus avoiding the need 31

to reverse the engine. With the deflection bucket fully deployed, the high velocity jet of water is directed down to the bed at an angle of about 30 degrees [Verheij, 2007 ; Hawkswood, 2013]. The other set produces a horizontal angle on the streamlines of the expelled water, generating the side thrust needed for turning, with plan rotation up to some 30 degrees typically. Because the pump is more efficient than the propeller, it is possible to reach higher speeds with the same power and less vibration and noise. These jets are usually installed in pairs to larger Catamaran Ro/Ro Fast ferries which have square cross section deflection buckets as illustrated in Figure 5.11.  Manoeuvring is very easy when one jet is pushing forward and the other pulling backward. The range of power can reach 26 MW. Severe scour has been observed from Catamaran Ro/Ro fast ferries which stern berth [Hawkswood, 2013]. Vessels reverse onto linkspan moorings with relatively low jetting action with the jet directed at the bed [Hawkswood et al., 2013] and push on to the mooring linkspan with high power (mooring jetting) until they are securely berthed. Smaller vessels which side berth do not display this mooring jetting action. However, deflected jets may be used for manoeuvring, and wash of the high velocity jet down closed structures must also be considered. For technical details we refer to information from suppliers (e.g. Wartsila, Kamewa by Rolls Royce, MJP Waterjets). Further information on water jet equipped RO/RO Fast Ferries can be obtained from Hawkswood (2013).

Figure 5.10: High speed Ro/Ro Fast Ferry with water jet propulsion (top left and right), Water jet common to passenger ferries with flow splitting deflectors (bottom)

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Figure 5.11: Position of deflector for manoeuvring (Wartsila Jet and deflection bucket in Hawkswood et al. (2013)) From top to bottom: forward thrust, reverse thrust, zero thrust

This jet/bucket configuration is common to vehicle carrying Catamaran Ro-Ro Fast Ferries, the reverse thrust position is used for mooring jetting. The deflection buckets also often rotate on plan by some 30º for manoeuvring. 5.3.3. Pump Jet Thrusters

Conventional propulsion systems are not always applicable in very shallow waters. For such circumstances the pump jet thruster has been designed. Originally designed for inland navigation, it is nowadays increasingly used as a robust manoeuvring system on ships and vessels of all kinds. Modern commercial inland vessels are equipped with a pump jet thruster (or the variant compound thruster) or 33

a transverse thruster. The latter one is in principle identical to the thruster of sea-going ships, but the engine power is less. Intake and outlet of a pump jet thruster are located in the keel of the ship, while a transverse thruster has an inflow located in the keel of the ship but the outflow can be located in the keel as well as at the sides. If the outflow is located in the keel, the jet is directed towards the bottom.  A pump jet thruster can be rotated through 360°, providing full thrust in all directions. The power of pump jet thrusters varies between 200 and 3000 kW, and developments are underway towards 3,500 kW (e.g. http://www.schottel.de/pdf_data/eng_SPJ.pdf ).

Figure 5.12: Operating principles and Illustration of pump jet thruster (Schottel)

34

Figure 5.13: Compound pump jet thruster (source:  www.veth-motoren.com)

Figure 5.14: Pump jet thrusters and transverse pump jet thruster with intake in the keel (bottom) (source: www.veth-motoren.com   )

35

5.4.

Relationship Between Propulsion Characteristics and Vessel Dimensions

Designers of quay structures need details of the vessels likely to use the facilities, including cargo, passenger and auxiliary vessels such as tugs in order to be able to make a preliminary or detailed design. However, it is recognised that this can be difficult, especially for a multi-user facility. Often, ship owners in competitive markets are also reluctant to disclose detailed information about their vessels. The following section gives an overview of typical propulsion installations which may be used for preliminary designs and, in the absence of more specific data and with suitable caution and sensitivity testing, for detailed designs. The installed power of thrusters (and main propulsion systems) depends on the ship type. Not all ship types have thrusters installed. Economic reasons and the destination ports may influence this. If thrusters are installed then tugs are often not necessary, although ships transporting dangerous cargoes, such as LNG carriers, very often must also be assisted by tugs. 5.4.1. Container Vessels

Nowadays, the installed engine power as well as the number of thrusters is increasing. Until recently large container vessels carry 12,000 TEU. Their installed power for the main propulsion system is about 80 to 90,000 kW while the installed power for each thruster is up to 3,000 kW. For the recently built ultra large containerships (ULCS) with a capacity of around 18,000 TEU the main power increases. In 2013 the 2 biggest ULCS are the Maersk Mv-Kinney Møller, from the Triple-E class2 of Maersk (18,270 TEU), with a length of 399 m, beam of 59 m, power of 2 * 29680 kW and 2 fixed-pitch 4 blades 9.65 m propellers and 2 bow thrusters of 2,500 kW and the Marco Polo of CMA CMG (16,020 TEU), with a length of 396 m, beam of 54 m, power of 80,800 kW (Wartsila), single shaft fixed pitch propeller and 2 bow thrusters of 1,800 kW [Dekker at al., 2013 ; DNV, 2013]. And on order for delivery in 2014 are the China Shipping Container Line vessels (18,400 TEU) with a length of 400 m, beam of 58.6 m (no further details available on propulsion systems). Designs for container vessels up to 22,000 TEU have been presented, which would be longer (extension from 400 m to 427 m), but not significantly wider (58.5 m or 23 rows of containers) or deeper than the Triple-E class [United Nations, 2011]. Considering the fact that some ports/terminals have already cranes that reach 24-25 rows (e.g. Wilhelmshaven, London Gateway), it cannot be ruled out that wider container vessels 23-25,000 TEU will be constructed in the future. Some engine manufacturers expect future installed powers of 100,000 kW for container vessels.

2 Referring

to Economy of scale, Energy savings and Environmental improvement

36

Figure 5.15: Predicted development of installed engine power (SMRC)3 as function of TEU

Recently, pilot cards were collected in Bremerhaven and Hamburg (Germany). They provide information on main propulsion systems as well as on thrusters for container vessels [Sievers, 2011]. Roubos (2007) also presented data for container vessels but for the Rotterdam harbour. Some of the data of the German and Dutch harbours are presented in the 3 figures below (Figure 5.16, Figure 5.17 and Figure 5.18). Relationships are derived between the installed thruster power (P thruster ) and the ship’s beam (Bs) and between the thruster diameter (D thruster ) and the ship’s beam as follows: P thruster  = 87.5 B s -1350

Equation 5-1

D thruster  = 0.05 B s  + 0.5

Where

Equation 5-2

Pthruster  = installed thruster power (KW) Dthruster  = thruster diameter (m) Bs

= beam of the ship (m)

Note that the total installed power is calculated which means that in the case of two thrusters the installed power should be equally divided. For the main propulsion system the following relationships can be used with P main the power of the main propulsion system and D main the diameter of the main propulsion system: P main  = 2800 B s -60000

Equation 5-3 Equation 5-4

D main  = 0.15 B s   + 1.2 3 SMRC

= service maximum continuous rating; i.e. the estimated power demand to enable the vessel to reach the required ship speed

37

Where

Pmain = power of the main propulsion system (KW) Dmain = diameter of the main propulsion system (m) Bs = beam of the ship (m)

    4    3&!!!     2     1       ) %"!!    !    (    0    - %!!!     /    !    ,$"!!    "     .    - $!!!    )    ,    "#"!!    +     *    )     $     $ #!!!    #    !    ( "!!    '    &     $    # !    !    "    ! !

+&$"! 6#-*( 7)-5#'8 9 :"!!)-*#5 /#-."0.", !/-0(!)-

#!

$!

%!

&!

"!

'!

.)#5 154

Figure 5.16: Relationship between beam (B s )  and total installed bow thruster power (P thruster  ) for container vessels

.", !/-0(!)- *)!)%(" %

    4    5     1    - $("    )    !    (    0    - $     /    !    - #("    )    !    )    5 #    #    &     * !(" ! !

#!

$!

%!

&!

"!

'!

.)#5 154

Figure 5.17: Relationship between beam B s   and bow thruster diameter D thruster  for container vessels (Rotterdam)

38

+&$"! 6#-*( 7)-5#'8 9 :"!!)-*#5 /#-."05#&' +-"+)$$)    4 #$!!!!    3     2     1 #!!!!!       )     $     $    ) *!!!!    +    "       + '!!!!    '    &    #    5 &!!!!       )    , $!!!!    "    +     * !    )     $     $ !    #    !    ( )$!!!!    '    &

#!

$!

%!

&!

"!

'!

.)#5 154

Figure 5.18: Relationship between beam (B s )  and total installed power for main propeller container vessels P main 

Note that the indicated relationships apply to average values of the ships’ dimensions. In individual, specific cases, the ships’ dimensions may differ considerably from these values, consequently the relationships should be used with care.  Also relevant is the distance of bow thrusters to a quay wall. As the beam of the ship at the bow is less than the maximum beam, the distance between the outflow of a bow thruster is considerable larger (depends on the beam of the ship) compared to the small distance between the amidship section and the quay face (about 1 to 2 m). From an analysis of container ships at the Rotterdam Harbours, Roubos concluded that the outflow point of the duct is typically at a distance of:  x  0.5Bs

5.4.2.

Equation 5-5

RoRo Vessels

Modern RoRo conventional vessels are equipped with two, sometimes three bow thrusters with about 1,500 kW per thruster. The diameter of the thrusters varies between 2.0 to 2.4 m. The main propulsion system comprises two propellers with in total 10,000 to 20,000 kW. 5.4.3.

Tankers

No data available, however tankers are in general not equipped with transverse thrusters. Recently, a tendency has developed in which tankers are equipped with 2 azimuthal thrusters for main propulsion and assisted with a bow thruster. For example, the 14,500 dwt Brostrøm D-class product tankers are equipped with Azipull propulsion. Rolls-Royce supplied each vessel with two Azipull  AZP120 thrusters rated at 2,380kW. They provide propulsion and steering and are supplemented by a Kamewa TT 1,850 tunnel bow thruster of 1,000 kW. Loaded service speed is about 13 knots, draught is 8 m.

39

5.4.4.

Fast Ferries with Water Jet Propulsion

Fast ferries can be compared with RoRo vessels if equipped with conventional propulsion systems. However, most fast ferries are equipped with a water jet system as main propulsion system, the very large ones with in total 4 water jets. Most of these high speed ferries are characterised as having catamaran hulls with wave piercing hulls, built in aluminium. Vessels above some 60 m long usually have twin ducted propulsion jets in each hull [Hawkswood et al., 2013] and their speed is typically greater than 28 knots [Evans, 2009]. In July 2013 the first ‘ High Speed ’ Fast Ferry Francisco has been delivered by Incat Tasmania on behalf of operator Buquebus for transport of (150) cars and (1,000) passengers between Urugauay and Argentina, with a design speed of 50 knots. The vessel is equipped with 2 Wartsila LJX 1720 SR water jets which are driven by two GE Energy LM 2,500 LNG gas turbines. Typical jet velocities while cruising are around 19 m/s and during manoeuvring around 13 m/s. Hawkswood (2013) records case histories of common Ro/Ro fast ferries in the UK, including reversal power and jet exit velocity into deflection buckets. General relationships are not available yet, but installed power can exceed 17,500 kW per water jet. For design the water jet type and velocity profile should generally be obtained from the manufacturer of the specific vessel or water jet.

Figure 5.19: Typical fast ferry (Wave piercing Catamaran, from Incat Catalogue)

Figure 5.20: Fast ferry hull and water jets [Hawkswood, 2013]

40

Figure 5.21: ‘H igh Speed ’ Fast F erry Francisco

5.4.5. Cruise Vessels

The cruise industry developments have been described by Grammerstorf and Schmenner (2012). Large cruise vessels of the post-100,000 gross tonne generation, such as Queen Mary 2, Celebrity series, Carnival Breeze and others with a length of around 300 m, width of around 40 m, draft between 8 and 10 m have an installed power for the main propulsion system ranging between 70,000 and 120,000 kW. Typical thruster systems are in the range of 3 to 4 thrusters, e.g Allure of the Seas: 4 x Wartsila 5,500 kW (diameter = 4.1 m), Celebrity: 3 x 3,000 kW (diameter = 3 m), Carnival Dream: 3 x 2,200 kW. 5.4.6. Supply Vessel, Tugs

In general, supply vessels and tugs are not equipped with thrusters. Supply vessels are equipped with a common main propulsion system with propellers. The installed power can be very high because supply vessels often have a towing task too. In order to be highly manoeuvrable, harbour tugs are very often equipped with cycloidal propulsion systems. Generally, the installed engine power in tugs varies between 1,000 kW up to over 3,000 kW per propulsion unit. Since most tugs are equipped with two propulsion unit s, the total engine power can be over 6,000 kW.  An important issue for tugs is the bollard pull. Based on literature, it can be derived that the bollard pull in tonnes is about 0.02 times the total installed engine propulsion power (kW). The maximum bollard pull at the moment for harbour tugs is about 200 tonnes.

41

5.4.7. Propulsion Systems of Inland Vessels

Size and propulsion system of inland vessels vary widely and depend on the type of vessel and the navigation conditions such as width and depth of the waterways and the hydraulic structures such as locks. Ship types to be distinguished are: conventional cargo vessels, container vessels, pushtow units, passenger ships, recreational boats and service boats such as tugs and patrol vessels. For the cargo vessels the available power for the main propulsion system is about 0.5 kW per ton ne loading capacity with a standard deviation of 30 %. For the largest ships the standard deviation is 20-25 %. Most ships are equipped with a double rudder system. Focussing on the European and US inland fleet nowadays typical characteristic ship dimensions are [MARIN, 2008 ; PIANC Report 99, 2008]: 



 

  

Conventional cargo ship DEK-type and RHK-type: length up to 85 m; 1 (some 2) propeller with a diameter of 1.2 to 1.6 m and an installed engine power 550 to 750 kW; installed bow thruster power about 250 kW (standard deviation 30 %) Modern new built conventional cargo ship Rhine-type and Rhine-max: length 110 to 135 m; mostly 1 and some with 2 propellers in nozzles (ducted propellers) with a diameter of 1.6 to 1.8 m and an installed engine power of 900 to 2800 kW; equipped with bow thrusters up to 700 kW (standard deviation 30 %) Container vessel (400 TEU): length 135 m; 2 propellers in a nozzle with a diameter of 1.6 to 1.8 m and an installed engine power of 2,000 to 3,400 kW; equipped with 2 bow thrusters European push-tow units: length 185-250 m; 2 or 3 propellers in a nozzle with a diameter of 1.6 to 2.0 m and an installed engine power of 900 to 2,800 kW; equipped with 1 or 2 bow thrusters or equipped with flanking rudders USA push-tow units: length 440 m; 2 or 3 propellers in a nozzle with a diameter of 2.7 m and an installed engine power of 900 to 2,800 kW; no bow thrusters or equipped with flanking rudders Passenger ships: 2 or 3 propellers in a nozzle with a diameter of 1.6 to 1.8 m and an installed engine power of 800 to 1,400 kW; equipped with 2 bow thrusters Tugs: 2 propellers in a nozzle with a diameter of 1.6 to 1.8 m and an installed engine power of 800 to 1,000 kW; equipped with 2 bow thrusters

Different types of bow thrusters are applied for inland navigation: transverse thrusters in a tunnel (Figure 5.22) with up to 350 kW and pump jet thrusters (see  Figure 5.14) up to 2,000 kW. The last type can also be built in older ships which originally were not equipped with a bow thruster.

42

Figure 5.22: Transverse canal type bow thruster on inland vessel: working principal (top left), installation (top right), illustrations (bottom) (Veth)

Based on an inventory the following relationships are found for the installed power of the bow thrusters of different types of inland vessels [Verheij, 2010]. For the main propeller, there is a relationship between the average installed power and the wet section of the vessel, which is a measure for the resistance of the vessel Figure 5.23: Pthruster , container  



Pthruster, general carg o

Pthruster,tanker 



2.0  Ls  T s  250

Equation 5-6

 1.75  Ls  T s  150

Equation 5-7

0.8  Ls  T s  100

Pthruster, passengers



Equation 5-8

275 kW 

Equation 5-9

Where LS = ship’s length (m) and Ts = ship’s draught  (m) 90 % of the vessels have a lower installed power than the above value increased with about 175 kW. 43

For the main propeller a relationship was found between the installed power and the total wet hull surface: (Figure 5.23): Pmain  0.66  Ls  2Ts  Bs 

Equation 5-10

Where Bs= ship’s width 90 % of the installed power is less than about 1.25 P main. +",)- 5#&' +-"+0$(&"' (8(!)5 ; -)(&(!#'6) %!!!

8 < =>??@A

$"!!

B

:  < =>CDDB $!!!

&'(!#$$)* +",)#"!!

#!!!

"!!

! !

#!!!

$!!!

%!!!

&!!!

"!!!

(/&+ $)'E/!F1BF*-#0E/!9.)#54

Figure 5.23: Relationship between resistance and installed power main propeller

Note that the indicated relationships apply to average values of the ships’ dimensions. In individual, specific cases, the ships’ dimensions ma y differ considerably from these values. Consequently, the relationships should be used with care. 5.4.8. General Relationships

Specific equations for all ship types of propellers and transverse thrusters are not available. Therefore, a more generally applicable method is presented. In general, the relationship between installed power P (kW), propeller diameter D p (m), and number of revolutions n reads [van Manen, 1958]: P

KQ n3 D5p

Equation 5-11

with KQ n

= momentum coefficient = rpm

44

Simplifying:

P  D p5  or  D p   .P 0.2

Equation 5-12

Based on a large amount of data for transverse thrusters, this theoretical approach results in:  = 0.6 (whereas for main propellers  = 0.7). Instead of the more theoretically based approach, it is also possible to derive empirical relations between the propeller diameter D p  (m) and the installed engine power P (kW), both for main propellers and transverse thrusters (see also  Figure 5.24) [Verheij, personal communication, 2004]:  D p  0.1636 P 0.3656

Equation 5-13

The relationships resulting from the theoretical and the empirical approach are not identical, but both can be used to estimate the diameter of ducted and non-ducted propellers. relationship between power P and diameter Dp of main propeller or bow thruster based on data from different sources 12

10

8    )   m    (   p 6    D

4

main ro eller 

2

bow thruster 0 10

100

1000 P (kW)

10000

100000

Figure 5.24: relation between installed engine power and propeller diameter

5.5.

Future Developments

Today the long distance transport of cargo is more and more carried out with huge specialised vessels like oil and ore carriers, LNG tankers and container vessels. Furthermore, feeder ships will remain and develop to transport goods to smaller ports or ports with limited draught. It is thought that this development will continue in the next coming decades. The speed of ore and oil carriers is about 15 knots while container vessels have an operating speed of 25 knots. The mentioned numbers are the limit for the present design of ships to transport goods economically.

45

 Another trend in ship design is that of the catamarans. These ships can sail with a speed of 60 knots and are today mostly used in ferry operations. Whether these ships will be further developed for cargo handling is still questionable because of fuel consumption, however car carriers are under design as illustrated in Figure 5.25. Competition with airfreight transport seems not viable because of cost and speed. In 2005 a zero emission car carrier (up to 10,000 cars  – which is the double of present capacity) has been designed by Wallenius Wilhelmsen. Dimensions would be 250 m LOA, beam 50 m, height 30 40 m and design draft 9 m. Maximum speed of the concept ship is 25 knots and service speed 15 knots. The vessel's propulsive power will also be provided by two variable-speed electric propulsion pods (2 * 4,000 kW) such as the Mermaid TM .

Figure 5.25: Zero emission Car Carrier (Wallenius Wilhelmsen)

Furthermore, the size of container vessels is increasing considerably. Modern engine suppliers expect a growth to 18,000 TEU with ship sizes of 470 m x 60 m x 16 m. To realise a ship speed of about 25 knots the required engine power is 100,000 kW. TEU

6000

8000

12000

18000

Name

Post-Panamax

Post-Panamax

Suez max

Post Suez max

Dwt

70,000

93,000

137,000

200,000

Length (m)

305

355

400

470

Beam (m)

43

43

52.5

60

Draugth (m)

12.5

13.6

14.6

15.7 (max 21 m, Malacca max)

Speed (kn)

25

25.3

25.5

25.5

Power (kW)

53,800

66,000

85,700

103,000

Table 5.1: Illustration of main characteristics of container vessels (Man B&W)

Other relevant developments are the modern cruise ships that are equipped with propulsion systems such as azipods (podded propulsors). Note that azipod propellers are 360 rotatable and that the spurt direction changes accordingly. These propulsion system can thus induce very high flow velocities at berthing structures.

46

6. BERTHING AND DEPARTURE PROCEDURES 6.1.

General Description

The sailing speed of a vessel during berthing and departure will be relatively low. One consequence of this low speed is that the ves sel’s manoeuvrability is significantly reduced and that the vessel cannot rely on the rudder to the same level as during regular sailing speeds. For this reason, assistance from tugs and bow thrusters is commonly used during berthing and departure. Specifics of the berth and the vessel usually determine the degree to which the vessel’s main propeller may also be used during these manoeuvres. Since proper control in multiple directions is needed but sideways push or pull by a tugboat will typically result in both a sideways force and a turning moment, normally two or more tugs are used. In some cases and to some degree a bow thruster can substitute the workings and/or need of a tug during berthing or departure. For more details regarding tug assistance in ports, we refer to Hensen (2003). Since most vessels spend only very limited time in ports, it is considered not worthwhile to equip the vessel with built-in equipment solely to aid in manoeuvring during berthing and departure. Common exceptions are vessel types like ferries, cruise vessels and containerships that are typically equipped with bow thrusters because of their higher incentives for not (or to a lesser degree) having to rely on tugboat assistance. While assignment and clearance of the berthing space at the terminal is typically done by the terminal operator, the actual berthing and departure operations of the vessel are managed from the vessel by the master and/or pilot. Main factors in managing a berthing or departure manoeuvre are typically wind and current. Either one can apply great forces on a vessel during such manoeuvres and will be a main driver in determining ultimate need for tugs. A certain vessel that may normally depart by use of main propeller and bow thruster may require tug assistance if wind or current are strong. Other important factors that play a role in determining the appropriate berthing and departure procedure in a specific circumstance are waterway width, presence of other vessels at berth, interaction with other ships, under keel clearance, vessel characteristics and type of structure (open versus solid). In some cases the vessel characteristics, the layout of the berth, the positioning of the cargo or equipment on the dock or the vessel dictate which side of the vessel will be moored against the dock and therefore also which direction the vessel will point during berthing and departure operations. In other cases, it can be left to the pilots or vessel operator and be decided based on situation specific preference. Typically, a vessel will slow down in its approach to the berth and will have any tugboats tie to it to provide control of the vessel when in close proximity to the berth. Tugboats will assist until the vessel is properly moored at which time they will cut loose and leave.

For berthing operations it’s essential to keep the approach speed very low, especially the lateral speed towards the berth. The large mass of the vessel and the mass of the water body moving in conjunction with the vessel (refer red to as the vessel’s virtual mass) make it impossible to make sudden changes to the vessels’ movement and can cause serious damage to the vessel and to structures or anything else in the vessel’s pathway.

47

For most vessels, a berthing procedure will typically take anywhere from 15 minutes to more than an hour. Departure procedures also vary widely, but typically take less time than berthing. For both berthing and departure operations, the slow response from the large mass of the vessel is a major driving factor. As part of the departure procedure from a berth, water will need to flow between the vessel and the berth. Simply increasing the force pulling the vessel away from t he berth will not proportionally increase the water flow rate or the departure procedure speed. Allowing water ample time to fill the space between the vessel and the berth while applying a constant force on the vessel directed away from the berth, is the main objective. That same concept  – though with reverse workings – applies to a berthing procedure where it will take time to divert any water trapped between the vessel and the berth. This is often practiced by having either a tug boat or the bow thruster apply force transverse to the berth for short periods (e.g. 30 seconds) at a time, followed by intermittent breaks to observe, control and adjust the departure speed or direction as needed. For further information on berthing and departure procedures, we refer to the Code of practice for design of fendering and mooring systems [British Standard, 1994]. 6.2.

Applied Engine Power During Berthing Manoeuvres

Since 1997 there is a dispute about the applied engine power during berthing and unberthing. However, this is related to main propulsion systems. F or bow thrusters it is recommended to estimate the thrusters jet velocities with 100 % of the installed engine power.

Figure 6.1: Illustration of possible berthing and unberthing manoeuvre

The applied engine power is not constant in time. In the first moments more power will be used. Moreover, the impact of the thrusters depends on the stage of the unberthing manoeuvre (Figure 6.1). Nowadays, it is unknown how long captains use their thrusters. Furthermore, it is important to realise that the installed power is increasing and not always designed for berthing/unberthing but also for carrying out manoeuvres in turning basins. In other words: applying 100 % of the installed power is a conservative estimate. This is underlined by results of an questionnaire of the Harbour Authorities of Antwerp resulting in 75 % of the applied power of the bow thrusters. Also in the Rotterdam Harbour figures less than 100 % are applied when designing a berthing structure. 48

Regarding inland vessels it is also recommended to apply 100 % of the bow thrusters power, although also in the field of inland navigation the applied power decreases with increasing installed power. Most ships have a thruster with maximum 250 kW. However, the largest ships have thrusters with installed power of about 700 kW, of which probably max. 60 % will be applied. For main propellers PIANC W orking group 22 (1997) recommended percentages of installed power to be used when estimating the flow velocities induced by propeller jets during manoeuvring (see Table 6.1). The recommended power was related to half ahead manoeuvring speed or about 10 % of the installed engine power. However, the EAU recommended other values: about 42 %. Both recommendations have been reconsidered (amongst others the working group had personal contact with professor K. Römisch). In addition, new information has been collected via pilot cards of (mostly) container vessels entering the harbours of Bremerhaven and Hamburg (both Germany), Rotterdam (The Netherlands) and  Antwerp (Belgium). Figure 6.2 and Figure 6.3 are based on the German results. Figure 6.2 shows the applied variation in relative power (applied power divided by the installed power) as function of the manoeuvring level. Figure 6.3 shows the relation between the percentage of the power and the percentage of the number of revolutions. manoeuvre

EAU [2004]

rpm

power

rpm

power

rpm

[%]

[%]

[%]

[%]

[%] average

Manoeuvre Max. installed power Full ahead service speed

New PIANC recommendations4[2011]*

PIANC [1997]

100

100

Full ahead  – manoeuvring

Standard deviation rpm

power

rpm

μ-2σ μ+2σ

100

[%] average

power

μ-2σ μ+2σ

100

100

85-87

51-73

57-63

18-25

65

10

44

86

28

9

63

100

Half ahead

82-87

55-65

43-48

8-11

53

8

37

69

15

5

32

Slow ahead

40-50

6-12

29-32

2-3

41

5

31

51

7

3

13

Dead slow ahead

30-35

3-4.3

14-16 0.3-0.4

30

4

22

38

3

1

5

Recommendations for manoeuvre

75

42

46

35-55

10

5-15

Table 6.1: Comparison of power and number of revolutions as function of the manoeuvre level for the old and the new recommendations 

4 Based

on pilot cards 2011

49

Figure 6.2: Applied variation in relative power as function of the manoeuvring level [Bruderreck et al., 2011]

Figure 6.3: relation between percentage of the power and percentage of the number of revolutions

New recommendations can be presented: for design purposes: we recommend in general to use an average of 5 to 15 % of the installed engine power (see Table 6.1). Most of the ships will use the ‘slow ahead ’ condition. Expressed as a formula:

50

Papplied   5  15%   Pinstalled  

Equation 6-1

Where Papplied = applied power and P installed = the installed power. The average value can be more specific for particular conditions: 1. for sheltered berth locations with a bed protection and no currents a value of 5 % might be applied (for example berthing in harbour basins). 2. for exposed berth locations with riverine or tidal currents and with a bed protection a value of 15 % is recommended (for example quay walls along the river); an alternative is to shift to th e ‘half ahead ’ condition in Figure 6.2. 3. in case the bed will not be protected and scouring is allowed it is recommended to use conservative values because calculations for depth of scouring are subject to more uncertainty than those for protective stone sizes. Subsequently, values including two times the standard deviation. 4. probabilistic calculations can be done by using the mean value and the standard deviation. The information above is mainly related to container vessels, but resembles also the PIANC 1997 recommendations. For other ship types larger percentages are recommended to be used. For example, bulk carriers about 30 % and smaller sea-going vessels and coasters about 40 % (information of the Rotterdam and Antwerp Harbour). If one wants to use rpm for computing the flow velocities the formula is:

napplied    35  55%   nmax

Equation 6-2

where: napplied  = applied rpm and n max = maximum rpm. For berthing areas for inland navigation it is recommended to apply 100 % of the installed engine power of the main propulsion system for the smallest ships, decreasing to about 50 % for the larger ones (especially the new type of vessels with length of 110 m or larger or the container vessels, see section 5.4.7). Summarising the following recommendations are presented: 

   

Thrusters: always 100 % of installed power, however when the thruster installed power is high relative to the average for a vessel’s class this may be too high and some reduction might be appropriate. Main propellers: 5 to 15 % of the installed power, but values up to 35 % (half ahead in difficult berthing conditions) cannot be excluded and depend on the ship type and the berthing conditions. Tug boats: always 100 % of installed power. If the berth is used by the same ships every time it is recommended to monitor the applied engine power. Inland navigation: thrusters 100 % and main propulsion system 50 to 100 %.

In Figure 6.1 the unberthing manoeuvre is shown for a vessel that is moored parallel to a quay wall. Figure 6.4 and Figure 6.5 show other examples of the areas affected by the main propulsion system and the thrusters (bow and stern).

51

Figure 6.4: Berthing and unberthing at a ramp

Figure 6.5: Berthing and unberthing out of a dock

52

7. DAMAGE AND FAILURE MECHANISMS 7.1.

Damage

Damage to port structures caused by propellers and transverse thrusters was first discovered at RoRo and ferry berths where ships berth without the use of tugs. Next, erosion and damage were discovered to exist along container terminals in Western Europe, illustrated by the findings of De Gijt in Rotterdam and Dueker in Hamburg [PIANC, 1997]. In the USA erosion was found to occur on the slopes of open piled structures, caused by bow thruster action. Catamaran Ro/Ro Fast Ferries with water jets are nowadays causing serious scour holes to port infrastructure, typically at the location of the mooring jetty. These early findings are still valid. A questionnaire has been sent to more than 20 ports both in the USA and Europe. The main findings can be found in  ANNEX C.

Figure 7.1: Erosion caused by main propeller and bow thruster in the port of Portland

Figure 7.2: Erosion caused by main propeller and bow thruster: illustration of model tests in Braunschweig [Drewes et al, 1995]

53

Figure 7.3: Scour caused by the water jet of Ro/Ro fast ferry [Hawkswood, 2013]

7.2.

Failure Mechanisms

Failure of a quay structure can be defined as (partial) loss of functionality of the structure. This chapter addresses failure mechanisms of berth structures specifically related to propulsion systems. Most failure mechanisms are directly or indirectly related to propulsion-induced scour at the toe of the structure or around its pilings. However, damage and failure can also occur due to other thrusterinduced impacts. For example, damage may occur to both solid and open berth structures due to floating or suspended material such as ice being forced into the structure by high jet velocities from thrusters. The concern in those cases would not be actual failure of the structure as a direct result of the thruster impact but rather damage to its protective coatings, which can lead to corrosion and deterioration over time and if not remedied ultimately to failure. In accordance with the previous chapters of this report, the failure mechanisms will be addressed separately for the different types of structures. 7.2.1. Failure Mechanisms for Solid Structures

We refer to Chapter 4 for the different types of solid structures (Figure 4.1 till Figure 4.5 and Figure 4.6 till 14).  A potential failure mechanism for any type of gravity structure would be loss of passive soil pressure. Since the bottom material in front of the berth structure is providing the passive soil pressure for the structure, a scour hole at the toe of the structure could easily lead to such loss. When the passive soil pressure is reduced (due to scour), the structure may rotate and move forward due to reduced resistance against the active soil pressure on the structure.

54

Figure 7.4: Gravity structure: loss of passive pressure

Deformation of sheet piles can lead to damage or failure of the berth structure for structure types like Figure 4.6 till Figure 4.8 as well as for Figure 4.6. The bottom material in front of the toe of the structure does provide passive pressure and determines the point of fixity for the sheet pile. Removal of that material due to scour will increase the load on the sheet pile itself and can lead to excess deformation which in turn may result in damage and/or failure. Note: Anchored sheet pile structures, anchors and/or friction slabs are an integral part of the structure and do provide in that sense additional strength at higher elevations of the sheet pile, but do not change the fundamental concept of this failure mechanism.

Figure 7.5: Sheet pile structure: loss of passive pressure

 Another failure mechanism for sheet pile structures is the loss or leakage of soil from behind the sheet pile. If a scour hole were to extend to (or close to) the depth of the sheet pile tip elevation, material from behind the sheet pile could wash out and undermine the landside part of the berth including any equipment and structures present on or behind the berth. In most situations, sheet piles will be driven to depths far beyond the reach of scour holes as that additional depth by itself is what the sheet pile structure relies upon for its stability and point of fixity. A common exception to that rule are sheet piles that form part of a cellular sheet pile structure (see type 1.5) where the sheet pile cell’s function is to contain soil as part of a gravity structure.

55

Figure 7.6: Sheet pile structure: loss of soil below tip

7.2.2. Failure Mechanisms for Open Structures

We refer to Chapter 4 for the different types of open structures (Figure 4.9 till Figure 4.11).  A potential failure mechanism for open berth structures is related to the slope underneath the dock. If scour in front of the berth would erode or undermine the toe of the slope, the passive resistance would be reduced. In that case, a sliding plane could develop and result in typical slope failure. This could both undermine the dock and land directly behind the dock, as well as cause damage to the piles penetrating that slope.

Figure 7.7: Open berth structure: loss of passive pressure leading to slope failure

If scour erodes the slope material itself or the slope protection material if present, the erosion could progress up the slope and consequently undermine the dock and land behind it.

56

Figure 7.8: Open berth structure: erosion and progressive failure of slope material/protection

 Any erosion or scour of soil material around piles caused by either direct exposure to thruster jets or by progressive erosion of a slope due to nearby thruster-damage has the potential to jeopardise pile capacity as well as pile stability and integrity. Depending upon their characteristics, piles are typically designed to provide their total bearing capacity through pile tip bearing capacity and/or surface friction capacity. Any level of erosion around a pile will have the potential to reduce a pile’s friction capacity as it reduces the embedded length of the pile and therefore the contact area between pile and soil. The pile’s tip bearing capacity on the other hand will typically only be at risk if scour or erosion extends to a depth of or close to the pile tip. In almost all cases typical pile lengths used for a dock structure will be beyond reach for depths from thruster-induced scour holes.

Figure 7.9: Open berth structure: erosion and loss of pile bearing capacity

In addition, piles supporting decks over armoured slopes typically resist horizontal forces by their embedment in the soil. Erosion around piles can therefore cause an increased risk of bending and buckling of piles due to the decreased embedment and longer unsupported pile lengths.

57

Figure 7.10: Open berth structure: erosion leading to pile buckling due to increased unsupported length

The likelihood of structural failure of bearing piles is low, but long before such gross deformations could occur, movements of the deck structures may have disrupted operations unacceptably. It is clear that as a consequence of these failure mechanisms, stable bed and slope protections are requested. In general the fault tree of failure of a granular protection system of berthing structures related to thrusters (as well as for main propellers) is given in  Figure 7.11. The figure does not include operational faults, ignoring of port-imposed rules for maximum power to be used, or misuse of azipods. Bottom material will be washed out due to a local scour hole

Or-gate 

Scour due to bow-thruster

Scour due to main-thruster

And-gate

And-gate

 

Remaining

Probability of not finding

Or-gate 

Design faults

Bow-thruster jet flow

Construction faults

Probability of general transport B=1,51

Or-gate 

And-gate 

Probability of continuous movement B=1,65

Top-layer too thin d
And-gate 

Or-gate 

Filter-layer too thin

Probability of not finding

Inaccurate delivery D50

Does not satisfy filter rules

Design faults

Or-gate 

Dump proces inaccurate d
Main-thruster jet flow

Construction faults

Probability of general transport B=1,51

Or-gate 

And-gate 

And-gate 

Probability of continuous movement B=1,65 D50<0,9D50

Or-gate 

And-gate 

Probability of continuous movement B=1,65

Inaccurate dredging d
Probability of continuous movement B=1,65

Top-layer too thin d
Or-gate 

Filter-layer too thin

Inaccurate delivery D50

Does not satisfy filter rules

And-gate 

Probability of continuous movement B=1,65 D50<0,9D50

Probability of continuous movement B=1,65

Or-gate 

Dump proces inaccurate d
Inaccurate dredging d
Figure 7.11: Fault tree of failure of a granular protection system of berthing structures

58

8. VELOCITY DISTRIBUTION 8.1.

Introduction

This chapter deals with different kinds of jets induced by propulsion systems and their effects on quay structures. The most important propulsion systems are: the main propeller(s) and the transverse thrusters (bow and/or stern thrusters depending on their position on the ship). Nowadays, also water  jets, azipods and Voith-Schneider propellers can be found. These systems distinguish themselves from the regular propellers in a way that there is no rudder. Azipods can turn around 360 degrees and are therefore relevant for erosion at quay walls. Also water jets are steerable, mainly to a maximum of 30 degrees to starboard or port and also towards the bottom: that is sufficient to create a strong water jet with flow velocities up to 20 m/s in the direction of the quay wall or the bed. Transverse thrusters are propellers placed in a tube inside the ship’s hull. Sometimes main propellers are placed in a nozzle (ducted propeller), in particular in inland navigational vessels because of the restricted water depth.  Azipods are considered as main propulsion systems (see section 8.3)

Figure 8.1: Relevant area in the flow field of a transverse thruster

59

Figure 8.2: Velocity distribution induced by a transverse thruster

In general, jets generated by propulsion systems can be compared with free jets. A free jet is defined as the water flowing out of an orifice into the surrounding water without any disturbance by lateral boundaries or walls that may hinder the spreading of the jet. In principle, all computation methods are based on the actuator disc theory assuming the propeller jet can be considered as a submerged free jet discharging out of an orifice into an infinite fluid and using the relevant equations for the zone of established flow presented by Albertson et al (1950): Vaxis



1

Equation 8-1

V0  D x  2C 

and  1 r2   exp   2 2   2C x 

V  x, r Vaxis

Equation 8-2

where Vaxis V0 Vx,r  D x r C

= flow velocity in the axis of the jet (m/s) = efflux velocity (m/s) = flow velocity in the jet at location x,r (m/s) = jet diameter at the beginning of the jet (m) = horizontal distance from the outflow of the jet (m) = radial distance from the jet axis (m) = coefficient (-)

60

Obviously, there are differences such as: propeller jets have a rotational flow velocity in the jet and swirl at the tip of the propeller blades. This results compared to free jets in a higher turbulence level, a shorter length of the flow establishment zone and a wider radial spread. Hamill & Johnston (1993) reported that the axial component is 10 times any other component, i.e. radial and tangential velocities (see  Figure 8.3), which do not need to be considered in the flow analysis of propeller or thruster jets.

Figure 8.3: Induced swirls and rotations

Figure 8.4: Differences in flow velocities between propeller jet and free jet 5 

In this chapter the induced flow velocities will be discussed in section  8.2 for bow thrusters and in section 8.3 for main propeller systems. Stability and scour aspects will be discussed in Chapter  10. In section 8.4 attention will be paid to numerical computation options. The effect of a rudder will not be discussed in detail. The ef fect of a rudder on the flow field depends on the propulsion system considered. First, the flow field of a transverse thruster is not influenced due to the absence of a rudder. Secondly, most main propellers are equipped with a rudder placed in line with the propeller axis, which will split the jet into two jets and creates higher bed velocities, or with a double rudder at both sides of the propeller, which will enlarge the zone of flow establishment. The effect of the presence of rudders is incorporated in the approach to estimate the flow velocities in the jet of the main propeller. Azipods are located behind the propeller and will tend to split the flow as a rudder does. In light of no viable modelling results it is considered prudent to treat the pod similar to the rudder effect for the calculation of bed velocities. Moreover, jets behind a forward or backward moving ship sailing with a speed higher than the manoeuvring speed used near berthing areas, will not be treated. Nevertheless, it is important to note that propeller jets behind moving boats differ from the conditions addressed by Albertson et al. (1950) for a free jet in the following way: 5 Read

Um as Vaxis, U0 as V0 and U as V in this figure

61

the channel bottom and water surface inhibit jet spreading a moving jet is discharging into a moving flow field the propeller jet has a radial component of velocity the rudder splits the jet into two jets the Kort nozzle (propeller placed in a tube) and open wheel (free propeller) are different from a free  jet out of an orifice

    

 Albertson et al (1950) determined a value of 0.081 for the coefficient C. The presented formulas assume a normal or Gaussian distribution of the flow around the axis and are valid in the zone of established flow. Closer to the orifice the flow has not been established yet and different formulas should be used. The rotation and swirl in a propeller jet (higher turbulence level) result in a shorter length of flow establishment in a propeller jet. 8.2.

Flow Velocities in Transverse Thruster Jets

8.2.1. General Equations

Based on the Albertson formulas the flow distribution for propellers can be derived : V0  C1 f n nmax Dp KT  

Equation 8-3

and V x,r

  D   A   p    x 

a

 1 V0 exp   2  2C2

  f  rudder , confinement   x2 

r2

Equation 8-4

where V0

= efflux velocity (m/s)

Vx,r  = flow velocity at location x,r (m/s) f n

= percentage of maximum number of revolutions (-)

nmax = maximum number of revolutions (s-1) Dp

= propeller diameter (m)

KT

= thrust coefficient or dimensionless relationship between propulsive force, number of revolutions and diameter of the propeller (-)

r

= radial distance to the propeller axis (m)

x

= distance to the propeller (m)

C1, C2 = coefficient  A

= coefficient

a

= exponent

For these coefficients and exponent a we refer to section  8.3.2 The formulas are only applicable in unrestricted water, so without any lateral or depth limitation. 62

German and Dutch researchers developed methods to estimate the flow velocities in propeller jets and in transverse thruster jet as a function of the installed power and geometrical dimensions of the berthing area. Formulas will be presented in boxes for a closed quay wall and a slope according to the German and the Dutch method. In addition, some remarks will be made how to deal with open quay walls. It should be noted that the two methods to estimate flow velocities can give rather different results, but the German and Dutch recommendations for calculating the necessary rock sizes for bed protection also differ. If the respective methods are used to also determine the rock sizes, the resulting designs will be quite similar. It is stressed that designers should adopt one approach entirely in order to avoid an unsafe result. Before presenting the prediction formulae for the velocity distribution in the jet, the efflux velocity V 0 is presented. Equation 8-3 can be simplified to compute the efflux velocity V 0 as follows : V0   nD p KT   

Equation 8-5

The equation is derived from the Bernoulli equation and the thrust force. A general value of  is 1.6 while values for K T can be derived from the Wageningen B- and K-series for propellers, which are ship specific [van Manen, 1956]. However, in many situations no values are available for the number of revolutions and/or the thrust coefficient KT. Therefore, empirical relationships have been derived, for example Blaauw & Van de Kaa (1978) presented an equation known in maritime engineering:

  f p PD  V0  C 3     w Dp2   

0.33

Equation 8-6

where PD = maximum installed engine power (W) f P = percentage of installed engine power (-) Values for the coefficient C 3 are: C3 = 1.17 for ducted propellers (propellers with a nozzle, see  Figure 5.4) C3 = 1.48 for free propellers Hamill & Johnston (1993) and Maynord (1999) also analysed the coefficient C 3 for tow boats on the Mississippi and found similar values. Since the effective diameter D 0 = Dp/√2 the Equation 8-6 can also be written as:  P  V0  0.79 C 3  D 2     w D0 

0.33

Equation 8-7

Substituting a value of C 3 = 1.48 for a free propeller then results in 1.17, which equals the value of C 3 = 1.17 for a ducted propeller. Therefore one equation for both types of propellers can be used:

 P  V 0  1.17  D 2     w D0 

0.33

Equation 8-8

However, the approach with D 0  will not be used hereafter, since it is preferred to use physical characteristics of the thrusters or propellers.

63

Thrusters can be considered as free jets with an outflow opening, for which the efflux velocity can be derived according to:   f PD  V0   C 3  thruster  2    w Dthruster 

0.33

Equation 8-9

with D thruster  = f thruster D p  and f thruster  = 1.02-1.05 and  = energy loss coefficient,  = 0.9 -1.0 and C3 = 1.48 for the following thrusters type (non-ducted azimuthal thrusters, ...) and C 3 = 1.17 for transverse thrusters and ducted azimuthal thrusters). In practice, we are unlikely to know f thruster   (since Dthruster   is the figure most likely to be quoted by manufacturers of thrusters) and we can write with sufficient accuracy: V 0,thruster

 P   1.15    thruster  2    w Dthruster 

0.33

Equation 8-10

Finally: in inland navigation many pump jets are installed. The jet of this type of thruster can be considered as special thruster for which we refer to section  8.3.4.3. 8.2.2. German and Dutch Approach 8.2.2.1.

Vertical Walls

We refer to Figure 8.1 for some definitions of parameters for a vertical quay wall.

64

German Method for Transverse Thrusters

The German methods as described in EAU and BAW are based on research by Fuehrer, Römisch & Engelke (1981) and Schmidt (1998). Vaxis ,thruster V 0  for x/Dthruster  < 1.9 Vaxis ,thruster

  x   1.9V 0,thruster    D thruster  

Equation 8-11 1.0

 for 1.9 < x/Dthruster 

Equation 8-12

With x the distance along the jet axis. Maximum flow velocity at the bed is: V bottom,thruster Vo,thruster

 L   a L 1.9    Dthruster 

1

Equation 8-13

With L the distance between outflow opening and quay wall corresponding to x t in Figure 8.1. The value of L follows from Figure 8.5: 1

   L

   a  ,    r    o    t    c    a    F

L/Db = 8

= 7; = 6; = 5; = 4; = 3

0,1 1

10 Distance from bottom, hP,b/Db

Figure 8.5: Factor  L as a function of the wall and bottom distance

Dutch Method for Transverse Thrusters

The Dutch method is based on research by Blaauw and Van de Kaa (1977), Verheij (1983), Blokland (1996) and Blokland (1997). Vb,max  1.0 V 0  Vb,max  2.8 V 0

 Dthruster hthruster  

for L/hthruster  < 1.8

 Dthruster

 L  hthruster

Equation 8-14  Equation 8-15

for L/hthruster  > 1.8

where L = distance between outflow opening and quay wall

65

8.2.2.2.

Slopes

The figure below shows the situation for a slope below the quay structure. In principle, a slope can be considered as an extreme situation of an inclined wall which will be discussed at the end of this sub section.

Figure 8.6: Transverse thruster flow directed towards a slope, valid for inland navigation vessels

Below the German and Dutch method to calculate the velocity on a slope, as caused by thrusters is explained. Physical model tests on this subject are also described in Dykstra et al. (2010). German Method for Transverse Thrusters above a Slope

 As for vertical walls, we refer to the German methods as described in EAU and BAW which are based on research by Fuehrer, Römisch & Engelke (1981) and Schmidt (1998) for the jet velocities in case of a slope. Slope

 Above the slope the area for flow propagation will be more and more reduced by the slope and the water level. Research by Schokking (2002) and Römisch (2006) resulted in a number of specific equations (derived for a slope of 1/3) : Vaxis,thruster  V 0,thruster  for x/Dthruster  < 1

Equation 8-16

0.33

Vaxis ,thruster

  x   1.0V 0,thruster     Dthruster 

Vaxis ,thruster

  x   2.3V 0,thruster    D  thruster 

 for 1 < x/Dthruster  < 5.375

Equation 8-17

0.825

for x/Dthruster  > 5.375

Equation 8-18

Dutch Method for Transverse Thrusters above a Slope

The Dutch method is based on research by Blaauw and Van de Kaa (1977), Verheij (1983) and Blokland (1997). Using the Dutch formulas for unconfined, free extending propeller jets, Blokland (personal communication) derived the following equations for the maximum current on a slope on the basis of research done by [Van Doorn, 2012].  xV  max  L

  2  K   1  1 K   

Equation 8-19

66

K  

b a   cot   

Equation 8-20

2

With A = 2.8 a ducted propeller and 1.95 for a non-ducted propeller a = 1 and b =15.4 (according to the Dutch formulas) f = Correction factor for the influence of the confinement of the jet by the slope surface (and by jetty piles if present) L = Horizontal distance along the jet axis between the slope and the beginning of the propeller jet xVmax = x coordinate of the location on the slope where the maximum current velocity according to the equation for a free extending propeller jet occurs x = horizontal coordinate from the beginning of the propeller jet α =slope angle For multiple propellers/transverse thrusters it is recommended to calculate and superimpose the 3-D flow fields of the individuals propulsors, or to use CFD techniques.

Figure 8.7: Transverse thruster jet above a slope

Van Doorn (2012) found from a limited number of model tests: f = 1.1 for a 1:2.5 slope with a smooth surface f = 1.1-1.2 for a 1:1.5 slope with a smooth surface f = 1.25 for a 1:1.5 slope with a rough surface (rock protection) f = 1.4 for a smooth 1:1.5 slope with jetty piles f = 1.64-1.7 for a rough 1:1.5 slope with jetty piles In the model tests Vslope,max occurs at a smaller value of x than x Vmax

8.2.2.3.

Inclined Walls

Recent German research resulted in formulae to predict the flow velocity and the scour depth in front of inclined walls [Drewes, BAW, Romisch]. They compared the results with the flow velocities in case of a vertical wall, i.e.  = 0.

67

Figure 8.8: Inclined walls – definitions

In principle, the approach for an inclined wall is as follows: for a wall with an inclination of  degrees with the vertical, the upwards part of the jet is larger than the downwards part. In other words: the flow velocity at the toe reduces. A reduction coefficient as function of the inclination has been determined based on model tests up to inclinations of 40 degrees. Obviously, for an inclination of 90 degrees the reduction must be 100 %. The final result is presented for the flow velocities in the following figure. c 



Qbottom , 

Equation 8-21

Qbottom ,  0

1,2 1 0,8   a _   c

0,6 0,4 0,2 0 0

20

40

60

80

degrees

Figure 8.9: Inclined walls: coefficient for flow distribution

68

100

In Table 8.1, the values for C a are presented for different inclinations of the wall.  = 0 (vertical slope)

 = 10

 =2 0

 = 30

 = 40

Qup/Q jet

0.5

0.61

0.71

0.81

0.88

Qbottom/Q jet

0.5

0.39

0.29

0.19

0.12

C

1.0

0.78

0.58

0.38

0.24

Table 8.1: Inclined walls: coefficient for flow distribution

8.2.2.4.

Open Quay Structures

Very often below the quay deck a slope will be present as illustrated in Figure 8.10 .Figure 8.10

Figure 8.10: Open piled quay structure

The figure illustrates that the following situations have to be considered regarding the flow field below the quay deck:   

Effect of piles Effect on the slope Effect of oblique jet

The effect of the slope has already been discussed in paragraph  8.2.2.1, while the effect of the oblique  jet (during unberthing) can be accounted for by considering the vessel at its real position, which will lead to a larger distance between the vessel and slope and or piles. More difficult is to take into account the effect of the piles. In any case it is a conservative approach not to take into consideration the obliqueness of the jet. If the vessel leaves the berth stern first, the possibility of the bow thrusters being closer to the slope than half the beam of the ship may have to be considered. The effect could be significant with breasting dolphins over a slope. Considering thrusters the flow direction will be perpendicular to a pile structure in most situations as shown in the figure. In general, the flow velocity directly adjacent of a pile will be twice the approach velocity [Breusers et al., 1977]: Equation 8-22 

Vpile  2 * Vapproach

69

Figure 8.11: Velocity in vicinity of piles

Recently, Van Doorn carried out scale model tests concerning the flow velocities induced by bow thrusters at an open berth structure as shown in Figure 8.10. An important result is that the flow velocities are higher than expected and the correction is given in Equation 8-19 to  Equation 8-20. For more information see Van Doorn (2012). 8.2.3. Transverse Thruster Jets Affecting Embankments

Figure 8.12 shows the damage due to thruster jets when a vessel is sailing in a canal.

Figure 8.12: Erosion of slope protection

70

In this situation the ship speed is very relevant. Based on theory and measurements a design graph, Figure 8.14) can be presented to estimate the flow velocities. It should be noted that these graphics describe the situation of an inland navigation vessel.

Figure 8.13: Vessel in stationary position and moving vessel (valid for bow thrusters of an inland navigation vessel)

The jet velocity near the bank will decrease with increasing vessel speed. Moreover, the induced return flow between ship and bank will result in bending of of the jet as shown in Figure 8.13. Based on a limited number of computations [Römisch, 2006] presented a design graph.

Figure 8.14: Erosion of slope protection valid in the situation of bow thrusters of an inland navigation vessel [Römisch, 2006]

71

8.2.4. Multiple Transverse Thrusters

More and more vessels are nowadays nowadays equipped with more than one transverse thrusters. To account a ccount for such multiple thrusters the same principles can be applied as for multiple main propellers. We refer to paragraph 8.3.5.1 paragraph 8.3.5.1 for the calculation methods and equations, in which h p should be read as the distance between the thruster axis axi s and the bed and y p should be read as half of the distance between the 2 axes of the thrusters. thrusters. 8.3.

Flow Velocities in Jets of Main Propulsion Systems

8.3.1. Introduction  – General Equations

Similar to thrusters two main approaches can be distinguished in literature to determine the flow velocity in jets of main propulsion propulsion systems:  

German approach: EAU (2009) and BAW Mitteilungen 88 (2005) Dutch approach: CIRIA (2007)

The guidance in PIANC WG 22 (1997) was based upon the German approach. The next figure shows the relevant parameters, while the specific formulas are p resented in boxes. It is emphasised that if the German approach or the Dutch approach has been selected, one stays with that approach for the calculation calculation of the protective scour system.

Figure 8.15: Definitions for jet of the main propulsion system (without rudder)

The outflow velocity V 0 can be estimated with (see also Section 8.2.1) Section  8.2.1):: Vo  1.6nrequired Dp KT    

Equation 8-23

With nrequired    fn nmax

Equation 8-24

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The value of f n equals the 35-55 % in Equation in  Equation 6-2 (see also Table 6.1). An average value is 45 %. For simple berthing conditions (low wind without currents) the value of 35 % can be applied; for complicated berthing conditions (strong wind with currents, narrow fairway) the value of 55 % is recommended which is about 20 % higher than the average value and can be considered as a safety factor of 1.2. Not included is a safety factor that takes into account the possibilities to repair a bed protection. This aspect should be considered when making a design.  A simplified version version reads: Vo  0.95nrequired Dp

Equation 8-25

However, in many situations no values are available for the number of revolutions and/or the thrust coefficient KT. Therefore, the empirical relationship in Equation 8-6 may be used as follows (see Section 8.2.1):

  f p PD  V0  C 3     w Dp2   

0.33

Equation 8-26

where PD = maximum installed engine power (W) f P = percentage of installed engine power used (-)(-); f p = 5 – 15% (see Equation (see Equation 6-1) Values for the coefficient C 3 are: C3 = 1.17 for ducted propellers C3 = 1.48 for free propellers 8.3.2. German and Dutch Approach

The methods for main propulsion systems are similar to those for thrusters, but the German recommendations add adjustments for jets confined by surfaces such as quay walls and make allowance for the effects of a rudder. Both methods assume the use of conventional propellers and need to be modified if du ducted cted propellers propellers are being considered. German Method for Main Propulsion Systems

The German methods as described in EAU and BAW are based on research by Fuehrer, Römisch & Engelke (1981) who derived values corresponding to A, C2 and gamma in Equation 8-4 as follows: Flow velocity along the axis in the zone of flow establishment

Vaxis  V o

x/Dp < 2.6

  x  Vaxis  2.6V o    D p   

1

Equation 8-27

in the zone of free jet propagation

2.6 < x/Dp

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Equation 8-28

  x  Vaxis  AV o    D p   

a

in the zone of restricted jet propagation

Equation 8-29

with  A  1.88 exp[0.092  h / D p ]

without a central rudder 6

Equation 8-30

with  A  1.88 exp[0.061 h p / Dp ]

with a central rudder

Equation 8-31

 A = 0.9 twin screw a = 0.6 influence of bottom and water surface only a = 0.3 extra influence for lateral quay wall (however A is not applicable then, but Equation 8-32 should be used with r = 0). a = 0.25 twin screw If a jet is deflected by a quay wall Equation 8-12 and Equation 8-13 should be used. Flow distribution in the jet

V x ,r  Vaxis  exp  22.2 r 2 x 2 

Equation 8-32

 A simplified approach for computing the maximum velocity at the bed, although this simplified approach overestimates the bed velocity for the present keel clearance ratios, reads:

 h p  Vb,max  E V 0    D p   

1.0

Equation 8-33

with E = 0.71 for seaborne vessels with a rudder E = 0.42 for seaborne vessels without a rudder E = 0.25 for inland vessels with a tunnel stern and a twin rudder configuration In any case V b, max < V0. Or

 h p  Vb ,max  Etwin V 0    D p   

0.275

with 0.9 < hp / Dp < 3.0

Equation 8-34

with Etwin = 0.42 for seaborne vessels with a twin propeller configuration and a central rudder Etwin = 0.52 seaborne vessels with a twin propeller configuration and a twin rudder [Römisch, 1993]: Führer & Römisch (1977) mention that the jet is angled down 12 degrees towards the bed (with rudder) or 13 degrees (without rudder). (See also BAW (2005))

6 Notice

that h is used and not h p

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Dutch Method

Blaauw & Van de Kaa (1978) and Verheij (1983) derived the following values for the variables: C2 = 0.18, A = 2.8 for ducted propellers and 1.95 for non-ducted propellers and a = 1. Substituting these values in Equation 8-4 yields:

D



Flow velocity along the axis

Vaxis

Flow distribution

V x , r  Vaxis  exp  15.4 r 2 x 2 

 (2.0 to2.8)V0

p

x

Equation 8-35 Equation 8-36

 According to Equation 8-36 the flow velocities at the bed can be calculated by substituting for r the distance from the propeller axis to the bed. Obviously, given the particular function, the maximum flow velocity at the bed can be expected below the propeller jet axis and the flow velocities will decrease slowly as one moves away from the propeller jet axis in the direction of the bank. The flow velocities at the bed can be characterised as a Gaussian or normal distribution. Notice that Equation 8-36 does not include the deflection of the jet due to rudder. The rudder angle must be considered explicitly in the vessel-berth geometrical configuration, by changing the jet axis according to the rudder angle. The maximum flow velocity at the bed occurs for h p/x = 0.18 (theoretical value, which is confirmed by tests of Verheij (1983) for propeller jets who found values between 0.12-0.22 and Rajaratnam (1976) for free jets: 0.1-0.25 This results in

 Dp Vb ,max  (0.2to0.3) V0   h p

Equation 8-37

with 0.216 for non-ducted propellers and 0.306 for ducted propellers. The Dutch and German method are both used next to each other. Recently, a study has been carried out in which the methods have been compared [Augustin, 2007]. The study shows differences, in particular regarding the computed flow velocities. The reason for the differences is that the German approach is based on a thorough research of all aspects: from the outflow via the flow velocities to the size of the bed protection. The Dutch approach was to develop a method to predict the required stone size. The velocities obtained should therefore only be used for calculations with the Dutch method and carefully be used for materials other than rock. Compared to the earlier PIANC report of 1997 the conclusions are:  

EAU and BAW are conservative PIANC (1997) was too optimistic (see section 6.2)

In addition, it should be noted that the Port of Rotterdam uses the Dutch approach successfully with respect to the amount of maintenance. Hamill & Johnston (1993, 2004) presented also a method to compute the flow field, however this method has so far not been adopted in any internationally recognised standards or guidelines. 8.3.3. Specific Conditions for Azipods and Azimuthal Thrusters

 Azipods are main propulsion systems. However, they are turnable and as such can be directed towards the berthing structures during manoeuvers. Furthermore, the appropriate equations should be used for design purposes. Azipods can safely be assessed as propellers with a rudder by the German method.  Azimuth thruster flow is similar to ducted propeller or propeller flow as the case may be. 75

8.3.4. Other Propulsion Systems

In addition to main propellers also other propulsion systems can be distinguished. We will consider water jets, Voith-Schneider propellers and pump jets. Contra rotating propellers are not discussed because of lack of information about the flow field behind this type of propulsion system. 8.3.4.1.

Water Jets

 A modern type of thruster is the water jet, which is installed on fast ferries. Characteristic for this propulsion system are the very high outflow velocities: up to 25 m/s, whereas conventional propellers have a maximum of about 8-10 m/s. Moreover, the direction of these jets can be towards the bottom of the harbor or waterway. The KAMEWA type has a maximum angle of about 45 degrees (more usual is 30 degrees), but e.g. the Lanzarote catamaran is equipped with a water jet that can direct the jet vertically towards the bed. This commonly occurs during mooring jetting. As an example, the flow velocities for the KAMEWA jet (when set to go astern) are presented in the next figure.

Figure 8.16: Example of jet velocity caused by a water jet (source: Kamewa)

Verheij (2007) derived the following set of formulae for the KAMEWA water jet: Equation 8-38

V x , r  Vaxis exp   92.75  r 2 / x 2 

Vaxis  12.4 V0 ( A0 / x)

Equation 8-39

1.17   0.33

Equation 8-40

V0  0.92  f P Pmain /   w A0 

With A0 the outflow opening (m 2). The outflow opening A 0 of the Kamewa water jets is 1 m2.

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The flow velocity distribution can be compared with the flow distribution behind a free jet, for which . V x , r  Vaxis exp  76  r 2 / x 2 

Equation 8-41

CFD modelling of Wartsila and Kamewa jets at the Wolfson Unit (2003, 2013) have provided estimates for the effect of the bucket deflection, twin jets merging and the effect of the jet pressure on the bed.

Figure 8.17: Example of the flow field of a Wartsila water jet [Wolfson Unit, 2013]

 Also low-powered water jets exist. Equations have been derived for a ferry equipped with a 750 kW Lips LJ90DT water jet Verheij (2007): V x , r  Vaxis exp  25  r 2 / x 2 

Equation 8-42

Vaxis  5.2 V0 ( A0 / x)

Equation 8-43

8.3.4.2.

0.85

Voith Schneider

 Another propulsion system is the Voith Schneider. Verheij (1990) derived a formula for the outflow velocity on the basis of measurements for the ferry to the Dutch island Texel:

  f p Pmain  V 0   0.75     w Dp hD   

0.33

Equation 8-44 

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Figure 8.18: Main dimensions of Voith Schneider propulsion system (brochure of Voith)

with hD is the height of the Voith-Schneider (B in Figure 8.18) and Dp the overall diameter J in Figure 8.18 ). If no detail information is available, the following relation between h D and Dp can be used : hD = 0.6 Dp (range between 0.5 and 0.75)

Equation 8-45

The flow distribution in the jet of a Voith Schneider propulsion system can be computed with the same formulas as for the main propeller or the classic thruster. 8.3.4.3.

Pump Jets

The outflow opening of a pump jet is located in the keel of a ship. This means that the jet is directed towards the bed. Recently, research has been done at Delft University resulting in preliminary equations for the prediction of the flow field in jets originating from pump jets [Manaois, 2012]. The efflux velocity is calculated according to 1  1  2  2 f P Pmain  3  8   D p  V 0  1,53     w Dp2   (nobh) cos( )        With

Equation 8-46 

n0 = number of openings b= width of the opening h = height of the opening    = angle between the axis of the jet and the plane of the opening

 And the complete flow field 0,799 V  x, r  x   r2  exp  5,56 2   2, 46   V0 x    D0 

Equation 8-47 

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With  D02    D p 

2

Equation 8-48 

Where coefficient ∆ = 50% - 70% (in this equation only) The outflow direction is about 30 degrees, but immediately after outflowing the direction changes to about 20 degrees. speed

Figure 8.19: Example of the flow field of a pump jet

8.3.5. Special Aspects 8.3.5.1.

Multiple Jets

The velocities in a flow field caused by two or more propellers can be calculated by linear superposition of the flow velocities caused by each propeller separately, as indicated by Verheij (1983) and BAW (2005) on the basis of measurements. Linear superposition however, results in axial direction in an increase of the total impulse of the superimposed jet, which is not correct physically. The total impulse in the jets remains constant in axial direction if the velocities of the single jets are superimposed quadraticly. However, this method can possibly result in an underestimation of the velocities at locations where the jets start to merge. Taking this into account it is recommended to apply linear superposition.

79

Figure 8.20: Multiple jets [BAW, 2005]

The maximum bed velocity caused by 2 jets at large distance behind the propeller can be calculated by the following simple formula, assuming quadratic superposition of the flow velocities in the individual  jets: Vb, max  V b, max, si ngle 2

hp / yp > 1

Equation 8-49 

With Vb,max = maximum velocity near the bed Vb,max,single = maximum velocity near the bed caused by one propeller hp = distance between propeller axis and bed yp = distance between the propeller axis and vessel axis (y p = ap/2) with ap the distance between the individual propellers Blokland (1997) derived equations for the maximum bottom velocity for 2 propellers in the case of a limited underkeel clearance (UKC) and assuming linear superposition of flow velocities in single jets using the Dutch formulas: Vb,max

 V b,max,single

  

Vb ,max  Vb ,max,single  (0.43to 061)

V0 D p  r p

hp

    2 Vb,max,single r p 

hp / yp < 0.578

Equation 8-50

hp / yp = 0.578 to 1

Equation 8-51

With r p 

h p2  y 2p

Equation 8-52

The coefficient 0.43 to 0.61 in Equation 8-51 is for non-ducted or ducted propellers respectively.

80

 As said before, for hp/yp > 1 (Equation 8-48) will result in a larger value of V b,max than Equation 8-49. Linear superposition thus results for h p/yp >1 in a too large maximum bottom velocity. For 3 propellers (with the middle propeller in the vessel axis) an analytical equation as  Equation 8-51 can‘t be derived, but the maximum flow velocity near the bed at large distance can be estimated with: Vb , max  V b , max,single 3

Equation 8-53

Main propulsion systems with two propellers are usually counter rotating. In that case the flow velocity can be slightly higher than computed by the above described superposition principle. In the absence of model tests an increase of 5-10 % is suggested. 8.3.5.2.

Rudder Effect

Transverse thrusters are not equipped with steering devices such as rudders. Conventional main propulsion systems have a rudder, but modern types such as azimuthal thrusters, water jets, pump jets and cycloidal propellers do not need rudders. The influence of the rudder on the flow field has been shown by various researchers, for instance by Fuehrer, Römisch & Engelke (1981). In essence, the rudder acts as an obstacle to the propeller jet, however due to the rotational nature of the jet, the rudder also acts as a lifting surface. The jet splits into two different jets, one directed towards the free surface and the other directed towards the bed which after hitting the bottom changes into a wall jet. The inclination of the jet axis is about 12 %, resulting in increased bed scour velocity. Deflection of the propeller jet by rudder deployment is well described in BAW (2005). 8.4.

Numerical Models

Using modern computational fluid dynamics (CFD) techniques the propeller induced flow field can be computed including the influence of jet orientation, influence of the distance to the wall, influence of underkeel clearance. Earlier studies at the Delft University showed that comparing a propeller jet with a simple water jet is not allowed, as is the basis for most existing propeller jet methods. In addition, the studies showed that the flow velocities in a bow thruster jet decrease slower than the flow velocities in a free propeller  jet. Subsequently, the best way to represent a bow thruster jet in a small-scale physical model is a propeller jet in a tube. Based on model test results a propeller jet in a CFD numerical model has been verified, however with two improvements:  

adding of tangential flow velocities incorporating a core zone in the jet

However, the model is still quite simple, because the propeller blades are not incorporated. The simulations have been carried out with the standard k -  turbulence model and the simulations agreed well with the results measured in the physical model. Simulation results show that: 1. flow velocities are after hitting the vertical wall, directed in all directions 2. the flow velocities parallel to a quay wall are of the same order as the flow velocities normal to the wall

81

3. the average turbulence intensity is about 35 % of the average flow velocity. These results mean that the maximum flow velocities are about 1.5 times higher than predicted by the analytical methods. If flow velocities are considered in axial direction only (i.e. normal to the quay wall) then the analytical methods predict the correct flow velocities.

Figure 8.21: Flow field between ship and quay wall [van Blaaderen, 2006]

Figure 8.22: Comparison between measured and computed flow velocities [van Blaaderen, 2006]

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Figure 8.23: Flow field induced by a transverse thrusters

Figure 8.24: Flow field induced by a waterjet [Hawkswood et al., 2013]

 Althoug  Although h the result resultss with with CFD methods methods are promisi promising, ng, the results results remain remain difficult difficult to valida validate te with prototype measurements, since such type of measurements are complicated to execute. Recently progress has been made with Smoothed-Particle-Hydrodynamics methods (SPH), as illustrated below where scour development due to a thrusters was simulated [Ulrich, 2013].

Figure 8.25: Scour development due to a transverse thruster [Ulrich, 2013]

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9. MA MATERIALS TERIALS AND TECHNOLOGIES 9.1.

Overview

To protect the bottom at the toe of the quay wall different materials can be used. The most commonly used materials are: 1. 2. 3. 4. 5. 6. 7. 8. 9.

Rock Rock grouted with liquid asphalt Rock grouted with hydro concrete Concrete block mattresses Concrete slabs Concrete mattresses Fibrous open stone asphalt mattresses Geosynthetics and geosystems Soft soil improvement improvement

It is obvious that specific documents have been prepared to describe the properties of these materials and their use in hydraulic, coastal and port engineering. Examples are PIANC WG 22 (1997), BAW (2005), EAU (2009) and the Rock Manual [CIRIA, CUR, CETMEF, 2007]. The reference book concerning geosynthetics and geosystems [Pilarczyk, 2000] and a similar book concerning asphalt prepared for Dutch Rijkswaterstaat [Van Herpen, 1985], to which the reader is referred for more details. Important properties of scour protection materials are in general : permeability, ground tightness, flexibility, reparability and durability. 9.2.

Rock

9.2.1. Material

 Armour material for a bed or slope protection is quarried rock with a grain size larger than 32 mm. Several types of stone are used : basalt, granite, syenite, quartzite and limestone. limestone. The rock density and the resistance to wear are important properties. properties. 9.2.2. Properties

The individual units lie apart from each other with limited interlocking, which obviously results in a higher chance for erosion caused by currents (loss of materials). The protection can be considered as having a relatively high turbulence, provoking scour around the protection system. A rock protection requires a minimum thickness. The system is an open bottom protection, as such requiring a filter layer to prevent that underlying soil will wash away. In combination with the use of a granular filter, a synthetic material or sand asphalt can be used. Flexibility of the protection system is high and damage (loss of stones) can be repaired rather simply. The damage of the underlying filter layer cannot be repaired in a simple way.

84

9.3.

Rock Grouted with Liquid Asphalt

9.3.1. Material

To improve a granular protection against erosion, the stones can be grouted with liquid asphalt mastic. Liquid asphalt is a mixture of asphalt mastic and aggregate. Asphalt mastic is a mixture of sand, a very weak f iller and bitumen (70/100). There are 3 different kinds of grouting with liquid asphalt: 9.3.1.1.

Stone confinement

In this procedure a specific quantity of liquid asphalt is uniformly applied to the entire surface. The method gives rise to a not entirely close structure. The asphalt only penetrates the upper part of the quarry stone layer.

Figure 9.1: Stone confinement

9.3.1.2.

Partial Grouting

The quarry stone is grouted in a predetermined pattern so that it clumps together to form larger stone masses.

Figure 9.2: Partial grouting

9.3.1.3.

‘

Full and Saturated’ Grouting

In this case all the voids in the quarry stone are filled with poured asphalt to form a slab -like cladding.

Figure 9.3: Full and saturated grouting

9.3.2. Properties

The bottom protection system is better protected against erosion and loss of materials, because of the grouting of the individual individual stones. The liquid asphalt itself is impermeable but only when the quarry stone is penetrated penetrated ‘full and saturated’ the whole of quarry st one and asphalt can also be considered impermeable. The system remains fairly flexible and repair is as easy as in the case of an ungrouted system.

85

9.4.

Rock Grouted with Hydro Concrete

This material is comparable to the one previously described, but the grouting is realized with a specific concrete which is applicable under water: hydro concrete or tremie concrete. Two kinds of mixtures can be used: open (permeable) or closed, depending on the application.

Figure 9.4: Use of hydro concrete for slope protection (Antwerp) [Interbeton]

9.5.

Concrete Block Mattresses

9.5.1. Material

 A block mattress is a prefabricated construction of blocks of concrete that are fixed to each other by using (synthetic) cables. These systems are also called Articulated Mats. The use of such systems has been reported for the port of Houston, port Canaveral, Ben Schoeman Quay in Cape Town, quay wall protection in Lome and further for quay slope protection for Berth 2 in Durban and Berths 1-3 in Walvis bay. The thickness of these systems varied from 600” over 800” to 1200”.

Figure 9.5: Use of concrete blocks against scour along a container terminal in Lome, Togo [Synthetex, 2014]

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Figure 9.6: Illustration of articulating concrete block mattresses [Synthetex, 2014]

9.5.2. Properties

 A block mattress can be considered as one layer of concrete blocks with a total size of around 10 m by 3 m and variable thickness. The mattresses together don’t form a homogeneous layer  so loss of bed material via the open joints between the mattresses is a disadvantage. The structure is open, hence to prevent scour of soil an appropriate granular or synthetic filter is required. Block mattresses are rather flexible: they can follow small settlements of the underlying surface. In case of damage the whole mattress will be replaced. The mattresses are available in heavy density (3,000 kg/m 3).

Figure 9.7: Illustration of control echosounding after placing articulating concrete block mattresses [Subcon, 2014]

9.6.

Concrete Slabs

9.6.1. Material

 A protection of concrete slabs is a construction of prefabricated ‘thin’  blocks of concrete that are positioned one aside the other, without using any (synthetic) cables. 9.6.2. Properties

 A concrete slab protection can be considered as one layer of thin concrete blocks and variable thickness (depending on the jet velocit y). The individual slabs don’t form a homogeneous layer so loss of bed material via the open joints between the mattresses is a disadvantage. The structure is 87

open, hence to prevent scour of soil an appropriate granular or synthetic filter is required or the shape of the slab should be designed to obtain soil tightness. The individual slabs are not flexible: flexibility is obtained via the joints. Concrete slabs have been used for the new container quay in the Port of Ngqura (South Africa) with a depth of -16 m CD. The (reinforced) slabs are 10 m wide and 0.6 m thick.

Figure 9.8: Use of concrete slab 7  (Port of Ngqura, South Africa) [du Plessis, 2010]

For the container terminal in the Port of Tanger Med II concrete slabs have been used for the scour protection in front of the gravity quay wall. The slabs have a thickness of 0.5m, due to the limited underkeel clearance.

Figure 9.9: Use of concrete slab (Port of Tanger Med II, Morocco) [IMDC, 2011] 7 Right

figure redrafted according to (du Plessis, 2010)

88

9.7.

Concrete Mattresses

9.7.1. Material

Concrete or grout mattress aprons are formed by divers rolling out mattress fabric underwater which is zipped together and pump filled with highly fluid small aggregate concrete. The fluid concrete is protected from wash out by the mattress fabric. The system typically comprises two layers of interconnected woven fabric as shown in Figure 9.12 which allows use on level beds or slopes. Mattresses are typically pump filled with a sand/cement micro concrete mix which has proven durable for performance periods of 50 years to date.

Joints between concrete mattress panels are formed using ‘ball and socket’ type shear joints, which produces an apron of interlocked concrete slabs underwater. Concrete mattresses have proven their usefulness since several decades. The system has been described for an application in the port of Belawan, under an open piled quay [Loewy et al., 1984] (Figure 9.10).

Figure 9.10: Use of concrete Mattresses in Belawan [Loewe et al., 1984]

Figure 9.11: Installation of mattresses on slope (left) and along quay wall (rolled out by divers (right)

89

9.7.2. Properties

Constant Thickness Mattress types are normally used to resist vessel actions on harbour beds and permanently submerged slopes. Constant thickness mattress types are specified by their thickness and surface undulation, smoother mattress types are more hydraulically efficient and flexuraly stronger. A 200 mm minimum thickness is recommended to berth beds where controlled maintenance dredging by dredging vessels is likely. Filter Point Mattresses are porous due to the woven in filters which allows use on slopes in tidal ranges and for wave heights (H s) typically to 1 to 1.5 m. A geotextile fabric is required under the mattress to protect against filter loss.

Figure 9.12: Filter point mattress (left) and constant thickness mattress (right) for Belfast VT4 Berth Scour Protection [Hawkswood et al., 2013]

Figure 9.13: Constant thickness mattress [Synthetix, 2014]

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Figure 9.14: Filter point concrete mattress [Synthetix, 2014]

Concrete mattresses have been used against water jet flow up to 12.5 m/s. Weep holes can be readily incorporated. In filled ground, or other cases where settlement is an issue, the mattress panel size can be reduced to increase flexibility. Mattress edges are normally laid into edge trenches with a rock falling edge ap ron provided. The system can form reliable joints and edges when installed using a suitable marine quality control system. 9.8.

Fibrous Open Stone Asphalt Mattresses

9.8.1. Material

Fibrous stone asphalt is a gap-graded mix of a selected stone size with fibrous asphalt mastic. The amount of fibrous asphalt mastic employed, results in fibrous open stone asphalt or fibrous overfilled stone asphalt. The addition of inert reinforcing fibres to the mastic makes it possible to add more adhesive bitumen, thus improving adhesion, resistance to hydraulic loads and flexibility without endangering the internal stability of the mixture. The extremely open structure of this asphalt means that it cannot be applied hot under water. When it’s used underwater it is installed in the form of p refabricated mattresses, laid with special techniques. The mastic which is the binder in the fibrous open stone asphalt is a bituminous product which displays all the characteristics of bitumen. Bitumen is a visco-elastic material, which means that it has both viscous and elastic properties. At lower temperatures or short-term loads its elastic properties dominate. When subjected to long-term loads the viscous properties dominate. For the fibrous open stone asphalt mattress a density of 1,950 kg/m 3 is assumed. Since fibrous open stone asphalt mats cannot be made under water, the asphalt mats are first prefabricated on the bank or quay wall and sunk afterwards. Generally, the mats are then placed directly on production pontoons. After the asphalt mats have cooled down for some days, they are brought to the installation location. Using a cable crane, placed on a large floating pontoon, the mats are sunk in the correct place. Using a special lifting frame below which are numerous hanging cables, the asphalt mat is lifted off of the production pontoon and lowered into place.

91

 After the asphalt mat has been lowered and exactly positioned the hanging cables are released by means of a hydraulic system. In this way the mats are placed one by one with an accuracy of 10-12 cm. Recent developments by using an imaging sonar during installation even improve the horizontal accuracy to 3-5 cm. Afterwards the joints between the asphalt mats are sealed, so that a complete soil tight protection layer is created. This can either be done with asphalt mastic or hydro concrete. Hydro concrete has been used in the Port of Antwerp for a number of applications: joints between mattresses in Delwaidedock, Marshalldock and North Sea terminal. The smooth connection between the different asphalt mats ensures that the protection layer remains completely flexible. Protecting a toe construction of embankments with fibrous open stone asphalt mats is an established method in Belgium. In the ports of Antwerp, Zeebrugge and Ostend several schemes have been carried out with fibrous open stone asphalt. A scour protection layer in fibrous open stone asphalt of 5 km long was installed in Deurganckdock in Antwerp (dry). Asphalt mattresses have been installed e.g. in the Port of Antwerp along the Cruise-terminal Quay, along the North Sea terminal, in Delwaidedock and along the oil jetty and container terminal at London Gateway. It should be noted that if the bed is not well leveled, such inaccuracies can lead to voids under the mattresses, leading to joints which are difficult to seal.

Figure 9.15: Dry construction of asphalt scour protection along quay wall in Deurganckdock (Antwerp) [DEC and Port of Antwerp]

Figure 9.16: Installation of fibrous open stone asphalt mattresses along North Sea terminal (Antwerp) [DEC]

92

Figure 9.17: Installation of Open Stone Asphalt mattresses in Delwaidedock (Antwerp) [Port of Antwerp] and in Vulcaanhaven (Rotterdam) [website Hesselberg Hydro]

9.8.2. Properties

The available test results and data f rom completed works show that fibrous open stone asphalt can most certainly withstand velocities up to 7 m/s. Fibrous open stone asphalt forms a relatively thin, homogeneous slab-like layer which is flexible and can withstand severe current and wave action. Fibrous open stone asphalt is permeable and as it is always used in combination with a (sand)filter, the filter properties will determine the permeability. Fibrous open stone asphalt is flexible and as such it can follow deformations of the bed. If there is damage to a mattress, the damage can be repaired by using liquid asphalt otherwise the whole mattress must be replaced. Research both in laboratory and in the field has shown that the good mechanical properties can be achieved when the material is exposed to cyclical loads and temperatures swings. These properties are, however, dependent on the satisfactory composition and processing of the materials. One must therefore take care to ensure that the preparation and application of the mix is carried out with skill and care as these factors can have a powerful influence on its durability. In case severer demands are made on the bituminous structure regarding resistance to hydraulic and mechanical loads, ability to deform to compensate for settlement or scour, the saturated mix should be chosen, i.e. fibrous overfilled stone asphalt. Proper need should nevertheless be given to the non-permeability of the protective layer and the consequence this may have on the overall stability of the structure. 9.9.

Geosynthetics and Geosystems

9.9.1. Material

The new innovative and so called low-cost methods based on geosystems have been applied successfully and on an increasingly larger scale. According to Pilarczyk (2001) the first category of applications are the ‘closed forms’  made of water-tight geosynthetics such as bags, mattresses, tubes and containers and are filled with sand, gravel or mortar. The second category are the ‘open 93

geosynthetic systems ’, consisting of a geosynthetic material anchored at both edges and having the ability to retain soil. For bed protection primarily closed forms are used.  A typical example of such protection system are the net filters, used for scour protection in the port of Wilhelmshaven and in the port of Antwerp. These units can weigh between 2 and 8 tonnes and can resist velocities up to 4.6 to 5.8 m/s.

Figure 9.18: Application of net filter system for scour protection (Wilhelmshaven) [Sumisho-Kyowa, 2014]

Figure 9.19: Installation of net filter system for scour protection (Wilhelmshaven) [Sumisho-Kyowa]

94

9.9.2. Properties

Due to the permeability of the individual elements, sand filled systems (bags, mattresses) should not be used in circumstances with velocities above 1.5 m/s, due to the internal migration of sand. As such sand-filled geosynthetics are less appropriate for scour protection due to thrusters. Internal erosion is not an issue for systems filled with clay, mortar or gravel. In general these structures are flexible and in case of damage repair is possible. 9.10. Soft Soil Improvement

Soft Soil Improvement (SSI) was first applied in 1993 after an exhaustive development and testing programme. Underwater, the system improves the bearing capacity of soils for construction works and remediates. SSI is a grouting technique that uses simultaneous hydraulic and mechanical blending to create a pre-determined configuration of soil-improved columns. This combination increases the overall ground bearing capacity in a particular area. One or more mixing blades are fixed to a central drilling rod. The leading edge of each blade has an array of mixing nozzles, while the trailing edge is equipped with grouting nozzles. As the blade moves in a cork-screw motion, grout is injected through each set simultaneously, providing both hydraulic and mechanical mixing and creating cylindrical columns. This localised ground improvement is sometimes used to enable deepening of gravity quay walls. It is not intended or generally feasible as bed scour protection.

95

10. DESIGN OF SCOUR AND BED PROTECTIONS 10.1. Design Philosophy

The main distinction in design philosophy is between:  A. Design to protect the bottom in front of the structure in order to avoid scour from occurring, or B. Design to protect the structure in order to avoid negative impacts to the structure resulting from scour

 Although in both cases the ultimate goal and result is the protection of the structure, in some cases the designer could decide to accept anticipated scour near the structure but secure the structural integrity in a different way, which in certain cases may be more cost-effective and suitable. It may be more effective and appropriate to design the structure for greater depths taking into account that deep scour holes may develop in front of it, than it would be to put all focus of the design in avoiding any movement or erosion of bed material. Additionally, there is also the option t o focus attention on avoiding scouring forces to happen, which is briefly addressed in section  10.7. This design philosophy issue is not much different from the usual design question what level of damage to accept in order to optimise a design for long-term functionality and cost-effectiveness over the lifetime of the structure. The answer to that question is highly dependent on the specifics of a situation and will have to be considered by the designer. Relevant factors that will have to be taken into account are:       

Cost (for both initial construction as well as maintenance) Environmental aspects (considerations related to allowing large movements of bed material versus installation of for example a hard bottom p rotection) Options to – and ease of  – performing monitoring and any needed maintenance Risk to the structure if scour would be more than an acceptable level and/or not detected in time Impacts and possibility of performing repair work in case damage to the structure would occur Effects on deepening or other berth modifications potentially required in future years Any other potential functions of the local bottom (e.g. nearby slopes, buried utilities/outfalls, etc.)

 After having decided about the design philosophy two other choices have to be made that are related to the design procedure shown in Figure 10.1. First, a choice has to be made about a deterministic or probabilistic computation of the bed protection or the expected scour hole depth.  A probabilistic  computation takes into account all uncertainties with respect to the data. In principle, this approach is preferred but it requires formulas that describe the phenomena correctly and in addition, it requires much more data. Since the probabilistic approach calculates with probabilistic density functions for all parameters, information is required on average values and standard deviations of the parameters involved. It is not always possible to collect all this information. It is recommended to consider all possible events by fault tree analysis. Roubos showed a procedure for a probabilistic approach (see fault tree in Chapter 7). Roubos (2007) presented a method taking into account the uncertainties in the design of the bottom protection near quay walls. His probabilistic approach is based on the reliability function:

 Z  R  S 

96

 

 with  Sthruster  V bed ,max  

and  Rthruster

 0.2to0.3 C 3   f p PD D p 

 Vbed , cr  Bcr

 

h p

 w

0.33

 

g (  s   w ) D50   w

With C3 = 1.17 or 1.48 and Bcr  = 0.8 to 1.2

Equation 10-1

Equation 10-2

Equation 10-3

Where S = surcharge (m/s) R = resistance (m/s) PD = maximum installed engine power (W) f P = percentage of installed engine power (-) Dp = diameter propeller (m) D50 = 50 % passing median stone diameter (m) Vbed, max = maximum flow velocity ‘near the bed’  (m/s) Vbed, cr  = critical flow velocity ‘ near the bed’ (m/s) Values for the coefficient C 3 are: C3 = 1.17 for ducted propellers (propellers with a nozzle, see  Figure 5.4) C3 = 1.48 for free propellers Values for the coefficient B crit,Iz  are: For standard situations (1/ B crit,Iz)2 = 3.0 [CIRIA, CUR, CETMEF, 2007], which results in Bcrit about 0.8. This value is smaller than the earlier value of 1.2 which is due to the lower turbulence in a regular flow compared to a jet. The coefficient 0.2 to 0.3 refers to a non-ducted propeller or a ducted propeller respectively. Equation 10-1 is a combination of and Equation 8-37, while Equation 10-2 is based on Equation 10-26. The method enables to compute the probability that a scour hole occurs of a certain depth. The equations as shown are valid for the situation without an obstruction in the propeller jet. If a quay wall obstructs the jet then the Equation 8-6 and Equation 8-14 or Equation 8-15 should be combined (if the Dutch method is applied).  

The deterministic approach requires the use of unique proper values of all parameters. However, this is not always possible. For example, it is often very difficult to get information on the number of revolutions of the propeller, while the installed power is known mostly. For readily repairable systems (such as rock) it is recommended not to design for emergency conditions but for reasonable design conditions, which should be based upon inspection periods, ability to repair and important conditions which regularly occur. For more details we refer to Chapter  11. The bed can be monitored on a regular basis in order to be able to repair damage in time. Where repairs may be difficult, or relatively costly, the protection should be designed for worst case events, to avoid failure of the protection during the design life.

The second choice to be made is about the method: the German or the Dutch method. Very essential is that if one makes a choice for a particular method, that one does not change halfway the computation to the other method. Changing induces big mistakes. There are certainly differences between both methods, but they both result in reliable protections or scour depth. The German 97

method is more detailed, while the Dutch method results quicker in answers. If one only need flow velocities then the German method is recommended. ship dimension

power (or rpm)

new or existing outflow velocity geometry quay German OR Dutch approach !!

local flow velocity

open structure closed structure

scour

depth scour hole scour extent

protection

type of protection thickness extent

deterministic OR probabilistic

Figure 10.1: Design procedure

Having made the necessary choices one can start the design. The first step is to compute the outflow velocity (see Figure 10.1). This requires information on the applied engine power or the rpm. If no information is available the ship dimensions can help, for example for container vessels a relationship has been presented (section 5.4.1) between the ship width and the installed power and the propeller diameter as function of the ship width. Knowing the outflow velocity, the berthing geometry is important:  

is it a closed quay wall or an open structure is it an existing structure that has to be upgraded or is it a new structure

This information determines how to compute the local flow velocity with the German or the Dutch method. 10.2. Scour 10.2.1. Scour by Transverse Thrusters

The flow velocities induced by a transverse thruster (or pump jets in inland vessels) may cause scour if they are higher than the threshold value of the bed material.

98

10.2.1.1.

Closed Quay Wall

Recently, Römisch (2004) modified equations derived by Schmidt for scour in front of a closed quay wall. For non-cohesive material they found (see also Figure 10.2 and Figure 10.3): 1st phase:

S  D85

13

 B   C m 0.1   for  Bcr 

 B  nd 4.6  C    m 2  phase:  D85 B  cr  S

1.0 

 B  Bcr

 1.4

Equation 10-4

2.25

 for

 B  Bcr

 1.4

Equation 10-5

with S = final (or equilibrium) scour depth (m)  B 

V bottom,thruster

Equation 10-6

 D85 g 

with Δ = relative buoyant density ( ρs –ρw)/ρw and Bcr  = 1.2 Cm = 0.3 during berthing manoeuvres which is most relevant for manoeuvring vessels and C m = 1.0 for steady state condition (which seldom applies in navigation situations). The flow velocity at the bed follows from equations in Chapter  8: V bottom,thruster V0,thruster

 L   a L 1.9    Dthruster 

1

for L we refer to Figure 8.5

Equation 10-7

with V 0,thruster

 P   1.15    thruster  2    w Dthruster 

0.33

Equation 10-8

99

Figure 10.2: Scour in front of a closed quay wall

Figure 10.3: Scour depth versus bed velocity in front of a quay wall

100

For cohesive soils we only consider the case of clay. Although the equilibrium of clay depends on the water quality and the material history (saturation and weathering) the stability is mainly influenced by the macro scale phenomena, that is, the magnitude of the clayey aggregates and the zones of weakness between the aggregates. Compacted clay has a high resistance against erosion and a low hydraulic conductivity (K) provided the clay is kept in sufficiently moist condition. However, K in structured (or unsaturated) soil is significantly higher owing to atmosphere, flora and fauna and varies from 10-5 m/s to 10-4 m/s. Therefore cr  varies from 2 kN/m2 (loose clayey soils or structured soil) to 25 kN/m2  (heavy clayey soils or compacted clay). For normal uniform flow conditions, i.e. for a relative turbulence intensity r = 0.1, the critical flow velocity ranges from 0.5 m/s to 2 m/s. For high turbulence intensities (r = 0.2) holds 0.25 m/s < V c < 1 m/s. Research on scour by jets has extensively be executed by Mazurek (2001) and Mazurek and Gheisi (2009). Based on the experimental work of Mirtskhoulava (1988), Mirtskhoulava (1991) and Hoffmans and Verheij (1997) the expression for cohesive sediments can be simplified:  8.8h   0.4  gDa  0.6C f ,M /         Da 

Vc  log 

Equation 10-9

With C f , M    0.035c

Equation 10-10

in which Cf,M is the fatigue rupture strength of clay which is linearly related to the cohesion c and D a (= 0.004 m) is the characteristic size of aggregates according to Mirtskhoulava (Table 10.1). By using r0   0

u* U0

g

  0

Equation 10-11

C 

where g   is the acceleration due to gravity, u * is the bed shear velocity and  0 (= 1.2) is a coefficient and the Chézy coefficient, defined as C  

 12h    k s 

g

ln 

 

Equation 10-12 

Equation 10-9 becomes Vc   0 r01  c , M  gDa  0.6C f ,M   /     

Equation 10-13 

With c , M  



  

/ 2.3

2

 0.4 

0.012

Equation 10-14 

in which  (= 0.4) is the constant of von Kármán and k s (≈ 1.5 Da) is the effective roughness.

101

Type of soil

Liquidity

n  = 0.30

n = 0.35

n = 0.40

n = 0.45

c

 

c

 

c

 

0 to 25

15

30

11

29

8

27

25 to 75

13

28

9

26

6

24

low plasticity

0 to 25

46

26

36

25

30

medium plasticity

25 to 50

38

24

33

23

high plasticity

50 to 75

n = 0.50

c

 

24

22

22

28

22

18

19

25

19

16

67

20

25 to 50

56

50 to 75

44

Index (in %)

c

 

16

12

12

46

18

35

14

18

42

16

31

11

15

35

12

28

7

Loamy sand

Loamy clay

Clay

0 to 25

79

21

Table 10.1: Estimates of c (in kN/m 2  ) and Φ (in degrees) for different values of the porosity n [Mirtskhoulava, 1988 ; Mirtskhoulava, 1991]

Table 10.2 shows some indicative values of V c for different qualities of clay under normal turbulence conditions (e.g. saturated clay at a river bed with r = 0.1) as well as highly turbulent conditions (e.g. structured soil with r = 0.2). Note that small-scale erosion tests carried out in the laboratory may result in larger values of V c because of the absence of weak spots and/or crack formation. Quality of clay

(1)

(1)

C clay,c

V c

(2)

V c

(kN/m2)

(m/s)

(m/s)

sand

-

< 0.4

< 0.2

 poor

< 0.15

0.4  –  0.8

0.2  –  0.4

average

0.15  –  0.33

0.8  –  1.2

0.4  –  0.6

good

0.33  –  0.75

1.2  –  1.8

0.6  –  0.9

> 0.75

> 1.8

> 0.9

very good (1)

r = 0.1 (clayey river beds; normal turbulence conditions)

(2)

r = 0.2 (structured soil; high turbulence conditions)

Table 10.2: Indicative values of V c   and C clay,c for clayey aggregates

For inclined walls the same equations apply to determine the scour depth, however the velocities are calculated according to the equations in section  8.2.2.3. A possible measure to reduce the scour depth is the jet deflector as illustrated in Figure 10.4.

102

Figure 10.4: Principle of a flow detector to reduce scour in front of a quay wall

10.2.1.2.

Open Quay Structures

Open quay structures consist of a superstructure built on piles with often, but not necessarily, also a slope. The piles form obstacles for the flow resulting in contraction between the piles and horse shoe vortices at the piles.

Figure 10.5: Scour at open berth structures

Chin et al (1996) published results of specific tests on scour at quay structures with a horizontal bed due to propeller jets. They derived the following equation with the densimetric Froude number F 0: Se  0.21D0 F 0   with F0  V0 / g D50

Equation 10-15 

Figure 10.6: Results of small scale scour tests [Chin, 1996]

103

 As mentioned before, mostly also a slope is present under an open quay structure. The above-mentioned results of Chin can be used, but also more general formulas presented in general scour manuals. For example, generally, the pile diameter is much smaller than the water depth in which case the following formula can be used to estimate the final scour depth [Hoffmans & Verheij, 1997]: S  2.0b

Equation 10-16 

with b = pile diameter. Mostly, a group of piles supports the superstructure. Then, the spacing S between the piles is important and the flow direction. If the spacing is larger than about 5b the scour holes of the individual piles do not influence each other. Else particular formulas should be used which take into account the different effects:   S  2.0Kb  with K  K group K orientation K shape

Equation 10-17 

The value of the various K-factors vary between 1.0 and 2.0. The box shows an example how to deal with complex pile configurations. Note that the parameters for pile diameter and spacing differ from the main text. In the box below the scour design formula for a single pile according to the FHWA circular HEC-18 is presented. For a pile group the result has to be multiplied with a spacing factor, thus: S pile group  Ks  S    with

K s  0.57 1  exp G / D   exp 0.5G / D 

104

Equation 10-18 

BOX scour at open berthing structures

Figure 10.7: Open berth configuration

The local pier scour equation recommended by Federal Highway Administration (FHWA, Circular HEC-18) [Richardson et al., 1995] was selected as a frame of reference for this analysis. The equation is stated as:

S D0.65 ( )0.43  =2.0 K  K K K Fr 1 2 3 4 h h

Equation 10-19

Where S = scour depth, m; h = flow depth directly upstream of the pier, m; K 1 = shape; factor K 2 = angle of attack factor; K 3 = dune factor; K 4 = correction factor for size of bed material; D = pier diameter, m; Fr = Froude number = U 0 /(gh)1/2; and U0 = mean velocity of the flow directly upstream of the pier, m/s.

  =     

Equation 10-20

 =     = 0.571 − /  +  ./

Equation 10-21 Equation 10-22

G= Spacing between the piles, as shown in Figure 10.7 D = the diameter of the piles K2 Spacing = correction factor for angle of attack on pile group

105

Figure 10.8: Projected width of piles for the special case of aligned flow

Figure 10.9: Projected width of piles for the general case of skewed flow

106

10.2.2. Scour Due to Main Propeller

For non-cohesive sediments the scour hole created by the jet of the main propeller is shown in  Figure 10.10 [Römisch et al., 2012] derived the following formulas: S  D85



h p D85



B



Bcrit 

Cad Cm ,r  a 

  1 

Equation 10-23 

with a = 0.65 and Cm,r   = 0.3 to 0.44 for rudder angles of 0 degrees to 40 degrees respectively during manoeuvring situations and C m,r  = 1.0 during stationary situations and 1

 h p    B C ad   17  0.9 1       1.0  D B crit   85   

Equation 10-24 

The coefficient Cm,r takes into account the effect of a rudder angle and the influence of manoeuvring relative to stationary condition.

Figure 10.10: Scour due to main propeller

The above equations are based on physical model tests on homogeneous soils as well as soil mixtures. The tests illustrated that in case of mixtures, the same scour depth occurred as for homogeneous soils if the mixtures were characterised by their D 85. 10.3. Design of Bottom Protection

In order to design a proper bed protection of riprap it is important t o continue with the selected approach. If you started with the German method to compute the flow velocities, than it is recommended to continue with the German formulas for determining the size of the required riprap. If you selected the Dutch method you must continue with the Dutch formulas. The German method uses formulas particularly suited and fitted for propeller jets, while the Dutch method uses general stability formulas such as the Izbash equation and the Pilarczyk equation. The presented methods are developed for stationary conditions near berths. However, nowadays vessels also use their transverse thrusters when sailing in narrow channels and the jets create damage to bank protections. This aspects will be dealt with at the end of the section.

107

German Method

The German stability approach is based on more than 40 years of research and published regularly [Führer et al., 1977 ; Drewes et al., 1995 ; Romisch, 2001 ; Schmidt, 1998]. The basic equation reads: Vcrit  Bcrit   D85 g 

Equation 10-25

with Bcrit = 0.9-1.25 [Führer et al., 1977]. Note that for regular turbulence conditions the value of B crit = 1.6-2.0 [Zanke, 2003]. In order to achieve stability the value of V cr   should be compared with the value of V bottom that can be computed with the formulas presented in Chapter  8. For the reason of using D 85 and not D50 we refer to section 10.2.2. In case of a propeller jet directed to a slope a procedure is presented in section  8.2.2.2. Also BAW (2005) presents a method to take into account the slope angle. Dutch Method

 As said the Dutch methods use general stability equations to estimate the required rock size of riprap protection. These formulas are developed on the base of a limited number of parameters involved. For instance the Izbash and the Shields equations are only based on the bottom velocity respectively bottom shear stress as attacking force. The armour layer should fulfil the following requirements:  

sufficient resistance against hydraulic loads fulfil filter requirements

Izbash found that there is a relation between the velocity “near the bed”  and the moment of incipient motion of grains, which he expressed as:  D50 

1 2

 Bcrit,Iz

2 V bottom

Equation 10-26

2g

where: Vbottom

flow velocity ‘near the bed’

Bcrit,Iz

coefficient (For standard situations (1/ Bcrit,Iz)2 = 3.0 [CIRIA, CUR, CETMEF, 2007], which results in Bcrit about 0.8. This value is smaller than the earlier value of 1.2 which is due to the lower turbulence in a regular flow compared to a jet.

D50

50 % passing median stone diameter

Of the more general formulas with optional parameters, the formula for current attack of Pilarczyk is presented in this section. Pilarczyk formula is also applicable for other types of bottom protections than riprap. Basically, the Pilarczyk formula equals the Izbash/Shields stability formula, but has been modified with extra factors for turbulence, slope angle, vertical velocity profile and geometrical characteristics. However, the Pilarczyk formula has not been validated for propeller flow and various types of bottom 108

protection other than rock, with only round estimates of coefficients provided initially by Pilarczyk (1990). Principally, the performance of scour protection joints and edges determine the performance and Pilarczyk's formula should be used with caution. The Pilarczyk equation reads [CIRIA, CUR, CETMEF, 2007] 8: For rock :  D   

0.035  cr

1

k hk sl

k t 2V 2

Equation 10-27

2g

In which:

Δ= D= g= V= Φ= cr  = ksl= kt = kh =

relative density characteristic dimension/thickness, Dn for rock gravity acceleration vertically-averaged flow velocity stability parameter critical Shields-parameter slope parameter turbulence factor depth parameter / velocity profile factor; Kh = 33/Λh 

[-] [m] [m2/s] [m/s] [-] [-] [-] [-] [-]

The Pilarczyk formula can be used for rock as well as related units or systems as blocks, block mats, mattresses and gabions, but it is important to note that the parameters have not been validated for propeller action. Suitable judgement should be exercised to ensure safe design of rock protection. For systems other than rock, it is suggested that the protection thickness obtained from the formula be checked against suitable testing and/or performance histories to ensure safe design. For the details see that particular section. In addition, the strength parameters m and Dn can be calculated with:  or  Dn50  0.84D50 and    m    m  w  1



for rock:  D   Dn50  3 M 50



for placed blocks and block mats: Dn = D = thickness of block, m = 



for gabions and mattresses: D n = d (= thickness of mattress) [m] and m = (1-n) ; the size of fill rock Dn. can be calculated as for rock but with a higher value of cr . The minimum thickness of the mattress is equal to d = 1.8 D n.

 s

in which: Dn. = equivalent diameter [m] D50 = 50 % passing median stone diameter [m] D = thickness of a system [m] m = relative density of a system [-] M50 = 50 % value of the mass distribution [kg] s = density of rock [kg.m-3]  = density of water [kg.m 3] n = porosity of stones [-], approx. n = 0.4 Some guiding values for these parameters are given below [Pilarczyk, 2001 ; Pilarczyk, 2010]. Note that the parameters have not been validated for propeller action.

8 Notation

from CIRIA, CUR, CETMET (2007), Chapter 5 Eq. 5.219.

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The stability parameter Φ depends on the application/placement. Placement

Continuous top layer

Edges and transitions

Riprap and placed blocks

0.75 to 1.0

1.5

Mattresses, gabions and washed-in blocks 9

0.5 to 0.75

0.75 to 1.0

With the critical Shields parameter cr  the type of material can be taken into account. Revetment type

Shields parameter cr 

Riprap

0.035

Loose, placed blocks

0.05

Blockmats, gabions and concrete mattresses 1 

0.07

The degree of turbulence can be taken into account with the turbulence factor. The following general values [Pilarczyk, 2001] are given as a point of reference. kt

kt2

Normal turbulence

1.0

1.0

Increased turbulence (i.e. river bends)

1.2

1.5

Heavy turbulence (i.e. hydraulic jump)

1.4

2.0

Sharp river bends (radius/width of river < 5)

1.4 to 1.6

2.0 to 2.5

Load due to water (screw) jet

1.7 to 2.0

3.0 to 4.0

Situation

It is important to note that originally Pilarczyk (1990) only mentions the lower values k t2 = 3.  Attention should be paid to the fact that in Equation 10-27, the turbulence factor, k t, is squared, similar to the velocity V. This is not the case in older versions of the formula. This calls for extra attention when copying kt values from literature. If possible, this turbulence factor, should be derived from the turbulence intensity by k t  

1  3r

[CIRIA, CUR, CETMEF, 2007],

Equation 10-28

1.3

with r = relative turbulence intensity (-). Experiments [Blaauw & van de Kaa, 1978 ; Blokland, 1996] indicate that the turbulence intensity near the bottom should fall in the range of 0.25 to 0.35 (see  Figure 10.11), resulting in turbulence factors ranging from 1.35 to 1.58. Römisch (personal communication) compared results of Deltares and German measurements and found similar results (see Figure 10.11, note that the turbulence definition is different). On the other hand, turbulence intensity can be considered to be 0.30 to 0.40 [Blokland, 1996 ; Blaauw & van de Kaa, 1978 ; Dargahi, 2003]. 9 Also

applicable for concrete slabs.

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The given relationship between turbulence intensity and turbulence factor (see above) results in k t = 2.5 (between 2.1 and 2.9), for turbulence intensities of 0.35 (respectively 0.30 and 0.40). These values are significantly lower than the turbulence factor k t2 = 5.2 to kt2 = 6 as proposed in CIRIA, CUR, CETMEF (2007). The values in CIRIA, CUR, CETMEF (2007) are not based on turbulence measurements, but on measurements of stone stability in combination with a current velocity calculated with the Dutch formulas. It should be noticed that the current velocity near the bottom calculated with the Dutch formulas is smaller than the actual velocity near the bottom, because the Dutch formulas do not take into account the influence of confinement of the radial jet expansion by the bottom (and the rudder). This underestimation of the actual velocity must be compensated with a larger value of (1/ B crit,Iz )2 in Equation 10-26 and a larger value of k t  in Equation 10-27. When designing a stone size using the Dutch formulas, it is recommended to use k t  = 5.2 to kt  = 6 as proposed in CIRIA, CUR, CETMEF (2007). When designing relatively impermeable scour protection types such as in situ concrete mattress or fully grouted rock, the method described in section  10.4 should be preferred to take into account the suction generated under a propeller. !

!

!

!

Figure 10.11:Turbulence intensity [Römisch]

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With the depth parameter K h, the water depth is taken into account, which is necessary to translate the depth-averaged flow velocity into the flow velocity just above the bottom protection. For propeller and thruster conditions we recommend to use K h ≈ 1.0. The stability of the bottom protection also depends on the gradient under which the revetment is applied, in relation to the angle of internal friction of the bottom protection. This effect on the stability is taken into account with the slope parameter k sl, which is defined as follows: 2

 sin     tan    k sl  1     cos  1     sin      tan   

2

Equation 10-29

with:

θ= angle of internal friction of the bottom protection material [°] (90° for concrete mattresses, 30 to 40° for sand-filled systems, and about 40° for riprap) transversal slope of the bank [°] α= 10.4. Design of Mattresses or Concrete Slabs

The increase in water velocity caused by the propulsion system results in an upward force on the bed. This force is quantified approximatively by applying Bernoulli’s Law:    p V  2     0  z      g g 2   w    

Equation 10-30

in which the following parameters are used:   

z: height [m] p: water pressure [kg/(m.s 2)] V: (bottom) velocity [m/s]

In case of a bottom protection (horizontal) the height-related component does not come into play. With respect to lift-up of the bottom protection, a lift factor, CL, needs to be brought into account. In this way the following relation is used to calculate the loss in (water) pressure, this is the upward force: 2  w  V bottom  p  C  L Equation 10-31 2

in which the following parameter is used: 

CL : lift factor [-]

This upward force needs to remain smaller than the submerged weight of the bottom protection: 2   w  V bottom C L   m   w   g  D Equation 10-32 2

in which the following parameters are used:  

m: bottom protection density [kg/m 3]

D: layer thickness of the continuous bottom protection [m]

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The minimal thickness of the mattress is proportional to the square of the bottom velocity:  D 

C  L

2   g

Equation 10-33

2  V bottom

In order to consider a certain degree of safety, a safety factor S f  can be used. For the continuous part of the protection C L = 0.5 [Raes et al., 1996]. As such, the combination S f . C L can be considered equal to the stability parameter Φ as used by Pilarczyk (for example if S f  = 1 to 1.5, than the combination is 0.5 to 0.75 which is identical to the stability factor as given in section  10.3). In dimensioning the continuous bottom protection an area-averaged bottom velocity (V bottom,average ) is considered, in which the area is equal to the size of the individual mattresses. Equation 10-33 does not take into account turbulence, but this can be incorporated via the K t factor. With regard to continuous or edge protection, the same stability considerations can be applied as proposed with the Pilarczyk equation. This relates to positive pressure from trapped flow causing uplift under mattress protections and would usually require substantial mattress thickness for stability. We refer to Wellicome (1981) to consider the suction distribution, caused by the inflow into the propulsion system. Mattress systems have joints and edges and it is recommended to design carefully to avoid underscour. For relatively impermeable and rigid panel concrete systems propeller suction uplift is the worst case [Hawkswood et al., 2013]. For relatively impermeable flexible systems with reliable joints and edges, design should be based upon local peak suction pressures, rather than area-averaged velocity. For protection against inclined water jets Hawkswood et al. (2013) provide a design method for in situ concrete protection types along with performance case histories for in situ concrete mattress types. 10.5. Extent of the Protection

The area along the quay wall to be protected depends on: 1. the influence area of the jets (transverse thruster and main propulsion jet) 2. the width of the passive soil volume in front of the quay wall required to ensure the geotechnical stability of the quay wall The influenced area depends on the berthing procedures: see the figures in Chapter  6. This gives an idea about the influence area of the thrusters and the main propellers. The following figures show details about these areas for the main propellers .

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Figure 10.12: Extent of the scour protection

 As can be seen seen a large area requires requires a protection. protection. For main propeller jets a sufficient protected width used by Deltares/Delft Deltares/Delft Hydraulics Hydraulics reads: 0, 5S propeller b protection  protection  bquay  0, 5 Bs  0, propellerss  0, 5 Dp  5m

Equation 10-34

where: bquay Bs Spropellers Dp

= distance between ship and quay wall (m) = ship’s width (m) = distance between main propeller shafts (m) = propeller diameter (m)

0.5Dp

5m

0.5S propellers

0.5Bs

bquay

Figure 10.13: Width of scour protection

For most conditions this will result in a wi dth smaller than the ship’s width. The extra width of 5 m is a value based on experience and takes into account the required issue of the geotechnical stability of the

114

quay wall. However, it is recommended to compute the required passive soil wedge (aspect 2 mentioned above). If the passive soul wedge is known, the required width of the bottom protection can be calculated as the width of the passive soil wedge enlarged with a strip that acts as a falling toe, following the scour of the adjacent unprotected bottom. The required width of the addition strip can be calculated as the product of the expected scour depth and the expected side slope of the scour hole when covered with a bottom protection [CIRIA, CUR, CETMEF, 2007]. In a German code (BAW, 2004) other formulas are presented: b protection 3 to 4  Dp  3to 5  protection  

b protection to 4  D p   3to 5  protection  2   3

for single screw vessels

Equation 10-35

for twin screw vessels

Equation 10-36

The equation for single screw vessels results in nearly identical values as the Dutch formula. The formula for twin-screw vessels seems to overestimate the area to be protected as it calculates values considerably larger than the ship’s width. The protected length along the quay is at least equal to the ship’s length enlarged with 50 m in front of the bow and 50 m behind the stern. However, this length depends depe nds on the berthing procedures [Blokland, 1997]. If the berth positions are at any time the same then the impact of the jets will always be at the same location. In that case the equations as presented by the BAW (2004) can be applied (see  Figure 10.12): 10.12):  Lmain   6 to 8  D p   3to 5 

Equation 10-37

 Lmain,2  3  D p   3 to 5

Equation 10-38

 Lthruster   3 to 4  Dthruster   3 to 5

Equation 10-39

Finally, it is recommended to compare the flow velocity at a certain distance of the quay wall with the critical flow velocity for the bed material at the same location. This determines the required width to be protected. 10.6. Repair or Upgrading of Existing Berths

Ships with a deeper draught and with greater capacity require adaptation of existing quay walls. Repair or upgrading of existing berths requires the same (or even more) attention for possible scour created by thrusters. Hence, the same principles concerning design as described above are applicable. We refer to the Handbook Quay Walls CUR (2005) for more details. The illustrations in this section are taken from CUR (2005). Figure 10.14 shows an example where a new sheet pile wall is placed in front of the old one and the vertical anchors together with the tubular piles are used as an anchorage for the entire structure.

115

Figure 10.15 shows an example of deepening of the water at the existing container quays in Rotterdam. In general, the following renovation or deepening measures can be taken regarding adaptation of the functions of a quay:    

reduction of the surcharge load of the area behind the quay adaptation of the ships regular inspection and monitoring adaptation of the quay structure structure

Old sheet piling

New sheet piling

New achors

    s      l   e      i     p     r    o      h    c     n Ground    a      l    e anchors      t   e      S

Figure 10.14: New sheet piling in front of existing quay (London, UK) [CUR, 2005]

116

Grout device Temporary filling

Caisson

Grout injection

Figure 10.15: Deepening in front of container quay (Rotterdam, The Netherlands) [CUR, 2005]

Fender structure Existing berthing

Sheet piling

Figure 10.16: Reinforcement of the front of the quay [CUR, 2005]

117

Existing rock protection

New rock protection

 Asphalt mortar 

Open stone asphalt

Figure 10.17: Fixation of the bottom in front of the quay [CUR, 2005]

In the Antwerp harbour jet high pressure grouting technique has been used to repair old quay walls. The high pressure causes intense mixing of grout and soil under the quay. As such, a row of piles is created under the quay wall to form a closed screen at the front of the quay wall. Subsequently, the harbour can be deepened.

G r   o u  t  a  n c  h o  r  

Existing quay wall

Grout piles

Figure 10.18: High pressure grouting technique under existing quay wall (Antwerp, Belgium) [CUR, 2005]

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In Hamburg a seriously damaged gravity wall has been renovated using a combination of long bearing sheet piles and short intermediate piles to take up the existing slope.

Existing quay wall Concrete pile fabricated in the field

Combined quay wall

Tension pile

Figure 10.19:Sheet pile restoration (Hamburg, Germany) [CUR, 2005]

10.7. Operational Guidelines

In addition to the option of either designing for the structure to withstand scouring in front of it or for the bed material in front of the structure to withstand scouring forces from propulsion actions, in certain cases there may also be the option to avoid or minimise scouring forces. This could be relevant to consider both for designers of new structures as well as for the operators of existing structures and it could be especially relevant for existing structures that are being exposed to higher forces and loads than anticipated during their design, due to developments in propulsion power and use. Besides structural measures to avoid or minimise scouring forces resulting from bow thrusters, such as installation of current deflectors or energy dissipation features at the face of the dock, operational measures can be considered as well. Factors to include when considering whether operational measures are a suitable solution or alternative to other means of scour protection are: 







Frequency of exposure to high propulsion loads or scouring action: e.g. for a berth that is only occasionally used by vessels with high propulsion forces, it may be more effective to provide a tug in those cases than to protect the berth against scouring. Variability in location of exposure to high propulsion loads: e.g. if exposure to scour is always at the same location of the berth, it may be easier to install dedicated very localised scour protection than when location of scour exposure varies Level of control over users of the berth and use of bow thrusters or high engine power during berthing: e.g. in case of a single-u ser berth it’s easier to optimis e between cost for the structure versus impacts to the vessels using the berth than it is in case of a multi-user berth. Impacts of operational measures to shipping: e.g. if availability of tugs is problematic, the requirement to use tugs could be unacceptable for vessels using the berth.

119



Temporary implementation of operational measures: e.g. operational measures could provide temporary relief or solutions while permanent protection is being considered, evaluated or prepared.

Either way, one needs to realise that a ship operator who has made an investment equipping a vessel with a bow thruster in order not to rely on tugs (or less so), will likely not look favourably upon restrictions on use of vessel propulsion and/or requirements to use more tugs.  An example of an operational measure is a requirement to use tug assistance in certain specific situations when the vessel’s own bow  thruster forces could otherwise be expected to be particularly high. Depending on the situation, following that thought a requirement for additional tug assistance could be limited to certain circumstances only, for example:    

when keel clearance is low (only deeply loaded vessels and/or only during low tide) when wind forces are high (only empty vessels and/or during high wind events) for vessels over a certain tonnage or weight for vessels with potentially most damaging propulsors

Other even simpler operational measures could be effective as well. A good example is to have periodic communications with pilots and vessel operators to assure they understand the issue. Sharing hydrosurvey information showing scour can help them to understand the relationship between use of thrusters and scouring effects and the impact that certain procedures or the modification there of can have.  Another option is some sort of signal system, simply calling attention to high flow from bow thrusters. It’s natural for pilots and masters to have the perception that a solid wall berthing structure is sturdier and thus less vulnerable than a pile supported structure. Not being aware that scour damage can pose a significant risk to either one type of structure, they feel more naturally inclined to limit use of thrusters near piles of which they can see actual movement or see and sense the structure’s vulnerability. Simply calling attention to high flow velocities generated by bow thrusters by installing sirens and/or flashing lights that would turn on as triggered by flow sensors near the berth could further increase attention to operators controlling how to apply thruster power.  As an illustration we refer to the guidelines for use of the cruise terminal in Antwerp: “Towing is not compulsory (between bollards 226 and 258/1 mats are positioned against the deepening of the river bed. This means that at quays S20 and S21 passenger vessels are allowed to use their bow and/or stern thrusters while mooring). For your information: the use of bow and stern thrusters alongside berths 19- 18B is however prohibited.” 

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11. DESIGN GUIDELINES AND RECOMMENDATIONS 11.1. Design Guidelines and Recommendations

In Chapter  10 the two possible approaches have been given to design berth structures with regard to thruster activities: either protect the bottom in front of the structure or allow for scour and design the structure accordingly. In this section a number of guidelines are formulated to make a safe, economic design of the structures, with proper selection of design parameters and safety coefficients.

Figure 11.1: Recommended procedure(s) for deterministic design

121

Suppose you go for a deterministic design. Based on the ship dimensions the first question to answer is the percentage of the installed power to use. The flow chart helps to select the proper value and refers to Table 6.1 in Chapter  6. However, keep in mind that the figures in Table 6.1 are based on modern container vessels whereas in the text also guidance is given for other ship types. In the flow chart distinction is made between allowing scour versus protecting the bed. If one consider to allow scour the stability of the quay wall is essential for a stable berth structure. For example, the sheet piling must be sufficiently longer than the scour depth due to the flow velocities in the propeller  jet. Therefore, it is recommended to use a high value for the applied power in the formulas to compute the flow velocities and the scour depth and extent. Taking the mean value increased with two times the standard deviation means a safe approach. In case of a bed protection a safety factor is taken into account at the end of the computation: flow velocities are calculated with the mean value of the applied power, but the dimensions of the rock or the thickness of a mattress are determined by using a safety factor. For a mattress a safety factor of 1.5 is recommended or alternatively  = 0.070 if  Equation 10-27 is used . For rock it is recommended to use a value for the mobility parameter of Shields of  = 0.035. This means a nearly stable rock protection. Table 11.1 shows conditions of the bottom protection for different phases in words and in values for the mobility parameter of Shields. If higher values for   are applied, for example   = 0.050 it is recommended to monitor the bed protections in order to take adequate (repair) measures if required. Condition of the bottom protection

Threshold of motion

  

Completely stable

Occasionally movement some locations Grains go for a roll; in places Frequent movement at several locations Grains go for a roll; at several places Frequent movement at many locations Grains go for a roll; at almost all places Frequent movement at all locations Grains go for a roll; at all places not permanent Continuous movement at all locations Grains go for a roll; at all places and permanent General transport of the grains Begin of the march of grains

0.030 0.035 0.040 0.045 0.050 0.055 0.060

Table 11.1:The phases as described by Breusers (1966) related to the Shields parameter (1936)

Nevertheless, before you can use the flow chart you have to know the installed power. That can be derived with the formulas and figures in Section  5.4.1 for container vessels, but you need to know the ship’s width or beam. The formulas allow also to make an estimate of the propeller diameter. For other ship types indications for the power are presented in Sections 5.4.2 to 5.4.6. In the annexes graphs are included to estimate dimensions of particular ship types. Propeller diameters can be estimated with the graph in Section 5.4.7. When designing the thickness of the protection system, we recommend to consider appropriate values of the turbulence factor : the following values are recommended: k t  = 2.5 (between 2.1 and 2.9). These values are significantly lower than the turbulence factor k t2 = 5.2 to kt2 = 6 as proposed in CIRIA, CUR, CETMEF (2007), but are more consistent with Dutch and German research. !

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When designing relatively impermeable scour protection types such as in situ concrete mattress or fully grouted rock, the method described in section  10.4 should be preferred to take into account the suction generated under a propeller. 11.2. General Recommendations

Obviously, more general recommendations can be given, for example:    



Scour protection systems should be permeable to avoid uplift pressures underneath the protection, especially in tidal waters Scour protection systems should be suitably flexible so that the protection can follow bed level changes Transitions between the bed protection and the quay wall should be filled or designed such that all soil loss is avoided Even so soil loss between individual mattresses should be avoided either by filling with an appropriate material such as hydro concrete or bitumen (depending on water depth, flow and wave conditions) or by using geotextile flaps and precise positioning systems (joints limited to less than around 3 cm). Protection systems with reliable joints give the best performance. Edges of mattress types and grouted rock should be protected from underscour with suitable edge protection details.

Finally, it is repeated that if one allows scour the German method is preferred, but most important is to stay to either the Dutch or the German method.

123

12. REFERENCES  Albertson, M.L., Dai, Y.B., Jensen, R.A., Hunter Rouse (1950): “Diffusion of submerged jets ”, ASCE Transactions Paper no. 2409, New York, 639-664.  Allison, J. (1993): “Marine water jet propulsion ”, Trans. SNAME, 101, 275-335.  Augustin, J. (2007): “Validation of different design criteria for scour protection measures ”, Lechtweiss-Institut fur Wasserbau, TU Braunschweig, Germany. BAW (2005): “Principles for the Design of Bank and Bottom Protection for Inland Waterways ”, Mitteilungen 88, Federal Waterways Engineering and Research Institute, Karlsruhe. BAW (2010): “Code of Practice, Principles for the Design of Bank and Bottom Protection for Inland Waterways ” (GBB), Federal Waterways Engineering and Research Institute, Karlsruhe. Bertram, V. (1999): “Practical ship hydrodynamics ”, Butterworth Heinemann. Blaauw, H.G. and van de Kaa, E.J. (1978): “Erosion of bottom and sloping banks caused by the screw race of manoeuvring ships. ” WLDelft Publication no. 202, Proc. 7th Intern. Harbour Congress,  Antwerp, May 1978. Blokland, T., Smedes R. H. (1996): “In situ tests of current velocities and Stone movements caused by a propeller jet against a vertical quay wall. ” Proc. 11th International Harbour Congres, 17-21 juni 1996, Antwerpen. Blokland, T. (1997): “Bodembeschermingen belast door schroefstralen. Huidige ontwerpmethodiek ”, Gemeentewerken Rotterdam, Ingenieursbureau havenwerken, Rapport 61.00-R94.038. Breusers, H.N.C., Nicollet, G. and Shen, H.W. (1977): “Local scour around cylindrical piers ”, Journal Hydraulic Res., IAHR, 15(3), 211-252. Brix, J. (1993): “Manoeuvring technical m anual”, Seehafen-Verlag. British Standard (1994): “British Standard, Maritime Structures, Part 4: Code of practice for design of fendering and mooring systems”, BS 6349-4. Bruderreck, L., Römisch, K., Schmidt, E. (2011): “Kritische Propellerdrehzahl bei Hafenmanövern als Basis der Bemessung von Sohlsicherungen ”, HANSA, no. 5. CEDEX (1996) : “Sovacación par actuación de helices ”, Clave:21-496-9-160. CEDEX (2011): “Efecto de socavación en las obras de atraque producida par la acción de las helices de los buques ”, Clave: 21-309-5-001. Para Puertos del Estado. CIRIA, CUR, CETMEF (2007): “The Rock Manual. The use of rock in hydraulic engineering ” (2nd edition), Manual on the Use of Rock. CUR (2005): “Handbook Quay Walls ”, CUR 211E, Taylor and Francis. De Gijt J.G.(1998): “Quay walls, Past, Present and Future ” (Kademuren, Verleden, Heden en Toekomst), Lezing voor GHR maart 1998. 124

De Gijt, J. G.(2010): “ A History of Quay Walls, Techniques, types, costs and future ”, PhD thesis, Technische Universiteit Delft. De Gijt et al. (2005): PAO course Ontwerp van Kademuren. Dekker, J., van Doorn, J. (2013): “Catching the whale, controlling large ships in ports ”, Port Technolgy International, pp 75-78. DNV (2013): “Container ship update ”, issue 1-2013. Dossche, M., Elskens F. and Sas M. (1992): “Research on the effect of propeller erosion on quaywalls and comparison of bottom protection schemes ”, Proc. 10th Intern. Harbour Congress, Antwerp, June 1992. Drewes, U., K.Römisch und E.Schmidt (1995): “Propellerstrahlbedingte Erosionen im Hafenbau und Möglichkeiten zum Sohlschutz für den Ausbau des Burchardkais im Hafen Hamburg ”; LeichtweissInstitut für Wasserbau der TU Braunschweig, Mitt. Heft 134/1995, Braunschweig. Du Plessis, G. (2010): “Construction of the Port of Ngqura, part 2: maritime and Civil Works ”, November 2006 to May 2011, Civil Engineering, pp 40-49. Dykstra, D., Tschirky, P., Shelden, J., Cornett, A. (2010): “Physical Model Tests of Bowthruster Impacts to Armored Slopes ”, Ports 2010, ASCE, pp 11-20. EAU (2009): “Recommendations of the Committee for Waterfront Structures, Harbours and Waterways”. Ernst & Sohn, Berlin. Evans, G. (2009): “Seabed protection systems to prevent scour from high speed ships ”, PhD thesis, Cranfield University. Fallintsen, O.T. (2005): “Hydrodynamics of High-speed Marine Vehicles ”, Cambridge University Press. Fuehrer, M. and Römisch, K. (1977): “Effects of modern ship traffic on inland- and ocean waterways and their structures”, PIANC, XXIVth Congress, Section I-3, Leningrad. Fuehrer, M., Römisch, K. and Engelke, G. (1981): “Criteria for dimensioning the bottom and slope protections and for applying the new methods of protecting navigation canals ”, PIANC, XXVth Congress, Section I, Edinburgh. Geisenhainer, P. and Aberle, J. (2013): “Scale Model Study of Propeller Induced Scour Development. In ‘Experimental and computational solutions of Hydraulic Problems’” , 32th Int. School of Hydraulics, Springer, pp 119-131. Grammerstorf, H., Schmenner, M. (2012): “Cruise industry developments in 2011 and 2012 ”, HANSA, International Maritime Journal, March 2012, pp 18-21. HANSA (2008): “International Maritime Journal ”, Sept. 2008, pp 38-47, pp 66-77, pp 96-104. HANSA (2013a): “International Maritime Journal ”, May 2013, pp 26-37. HANSA (2013b): “International Maritime Journal ”, June 2013, pp 51-55. 125

Hawkswood, M. and Allsop, W. (2009): “Foundations to Precast Marine Structures, Coasts, Marine Structures and Breakwaters ”,Edinburgh. Hawkswood, M., Evans, G. and Hawkswood, G. (2013): “Berth Scour Protection for Fast Ferry Jets ”, ICE Marine Structures and Breakwaters, Edinburgh. Hensen, H. (2003): “Tug use in port ”, The nautical institute, London, 2 nd edition. Hoffmans, G.J.C.M., Verheij, H.J. (1997): “Scour manual ”, Balkema, Rotterdam. IMDC (1993): “Propeller induced velocities ”, Internal Report, prepared for PIANC  – PTC II Working Group 22. IMDC (2011): “Tanger Med II, Scour protection against propeller wash ”, I/NO/12080/11.193/PDV, prepared for Besix. Loewy, E., Burdall, A.C. and Prentice, A.G. (1984): “Revetment construction at Port of Belawan, Indonesia”, Flexible Armoured Revetments, Thomas Telford. Manaois, J.R. (2012): “Pump jets in inland navigation ” (in Dutch), MSc thesis, Delft University of Technology, Delft. Man B&W Diesel (2001): “Basic Principles of Ship Propulsion ”. MARIN (2008 ): “New inventory of ship manoeuvring devices ”  (in Dutch), report 22788.600/3, Wageningen, The Netherlands. Mazurek, K.A. (2001): “Scour of Clay by Jets ”, PhD Thesis, University of Alberta, Edmonton, Alberta, Canada. Mazurek, K. and Gheisi, A. (2009) : “ Assessment of the Erodibility of a Cohesive Soil using a Submerged Circular Turbulent Impinging Jet ”, 33rd  IAHR Congress: Water Engineering for a Sustainable Environment. Miller, C. (2008): Syllabus PAO, Quay Walls. Mirtskhoulava, Ts. Ye., (1988): “Basic physics and mechanics of channel erosion ”, Gidrometeoizdat, Leningrad. Mirtskhoulava, Ts. Ye. (1991): “Scouring by flowing water of cohesive and non-cohesive beds ”, J. Hydr. Res., 29(3), 341-354. PIANC (1997): “Guidelines for the design of armoured slopes under open piled quay walls ”, Supplement to Bulletin 22, Brussels. PIANC (2008): “Considerations to reduce environmental impacts of vessels ”, Report 99. PIANC (2014): “Harbour Approach Channels Design Guidelines ”. PIANC Bulletin and Magazine :  PIANC Bulletin 58 (1987): contains 7 papers on “erosion problems caused by propellers ”.

126

       

PIANC Bulletin 89 (1996): paper by Hamill et al. on “Estimating the velocities in a ship's propeller wash”. PIANC Bulletin 91 (1996): paper by Hamill et al. on “The influence of a revetment on diffusion of a propeller wash ”. PIANC Bulletin 102 (1999): paper by Maynord on “Inflow zone and discharge through propeller jets ”. PIANC Bulletin 106 (2001): paper by Hamill et al. on “The effect of rudder angle on the scouring action produced by the propeller wash of a manoeuvring ship ”. PIANC Bulletin 109 (2002): paper by Romisch et al. on “Input data of propeller induced velocities for dimensioning of bed protection near quay walls ”. PIANC Bulletin 114 (2003): paper by Schokking et al. on “Bowthruster induced damage ”. PIANC Magazine 128 (2007): paper by Roubos on “Dealing with uncertainties in the design of bottom protection near quay walls ”. PIANC Magazine 140 (2010): paper by Sohngen and Kayser on “Design of bank and bottom protection ”.

Pilarczyk, K.W. (1990): “Coastal Protection ”, Proc. of a short course, published by A.A.Balkema, Rotterdam. Pilarczyk, K. (1998): “Dikes and Revetments ”, A.A. Balkema, Rotterdam. Pilarczyk, K. (2000): “Geosynthetics and Geosystems in Hydraulic and Coastal Engineering ”, Taylor & Francis, London and New York. Pilarczyk, K. (2001): “Unification of stability formulas for revetments ”, Proc. IAHR Congress, Beijing, China. Pilarczyk, K. (2010): “Design of alternative Revetments, in Handbook of Coastal and ocean Engineering”, ed Y. C. Kim (world scientific), pp 479-520. Prosser, M.J. (1986): “Propeller induced scour ”, BHRA report RR2570. Rajaratnam, N. (1976): “Turbulent jets”, Elsevier, Amsterdam. Rajaratnam, N. (1981): “Erosion of sand beds by submerged impinging circular turbulent water jets ”, University of Alberta, Edmonton, Alberta, Canada. Rajaratnam, N. (1981): “Erosion of loose polystyrene bed by oblique impinging circular turbulent air  jets”, University of Alberta, Edmonton, Alberta, Canada. Raes, L., Elskens F., Römisch K. and Sas M. (1996): “The effects of ship propellers on bottom velocities and on scour near berths and protection methods using thin flexible revetments ”, Proc. 11th Intern. Harbour Congress, Antwerp, June 1996. ROM (2000): “Recommendations for Maritime works ”, Ministry of Public Works, Spain. Römisch, K. (1993): “Propellerstrahlinduzierte Erosionserscheinungen in Häfen ”, HANSA Schiffahrt, Schiffbau, Hafen, 130. Jarhgang, nr.8, 1993. Römisch, K. (2006): Binnenschiffahrt, Nr 11.

“Erosionspotential

127

von

Bugstrahlrudern

auf

Kanalböschungen ”,

Römisch, K. and Hering, W. (2002): “Input data of propeller induced velocities for dimensioning of bed protection near quay walls ”, PIANC Bulletin 109, Brussels, January 2002. Römisch, K. and Schmidt, E.. (2012): “Durch Schifspropeller verursachte Kolkbildung ”  (Scour caused by ship propellers), HANSA, no. 9 (2012). Rowe, R.W. (2000): “The Shiphandler’s Guide” , The Nautical Institute, London. Schmidt, E. (1998): “ Ausbreitungsverhalten und Erosionswirkung eines Bugpropellerstrahls vor einer Kaiwand”, Dissertation am Leichtweiss-Institut für Wasserbau der Technischen Universität Braunschweig. Schwarze, H., et al. (1995): “Modelluntersuchungen zu Propellerstrahlinducierten Strömungen an Schiffsliegeplätzen mit Unterschiedlichen Massnahmen zum Erosionsschutz ”, Franzius-Institut, Mitteilungen Heft 76, Universität Hannover. Sievers, M. (2011): “ Auswertung und statistische Analyse von Pilot Cards zur Ermittlung von Fahrtstufen bei An-und Ablegemanövern ”, Bachelorarbeit der Hafen City Universität Hamburg, Department Bauingeniuerwesen, Fachbereich Grundbau und Wasserbau. Sumisho-Kyowa (2014): “Filter Unit, natural protection for the environment ”. Synthetex (2014): “Berth Scour Protection ”. Thoresen, C. A. (2003): “Port Designer’s Handbook” , Recommendations and Guidelines, Thomas Telford Limited, London. Tutuarima, W.H. and W. van Wijk (1984): “ProFix mattresses  –  an alternative erosion control system”; In: Proc. Intern.Conf. on Flexible armoured revetments incorporating geotextiles, 29-30 March 1984, Thomas Telford Ltd., London. Ulrich, C. (2013): “Smoothed-Particle-Hydrodynamics simulation of Port Hydrodynamic Problems ”, PhD thesis, Technischen Universität Hamburg-Harburg. United Nations (2011): “Review of Maritime Transport 2011 ”, Technical report, United Nations Conference on Trade and Development. Van der Weijde, R.W., Heijndijk, P.J.M., Noordijk, A.C., Kleijheeg, J.T. (1992): “Scouring by ships’s propellers”, Tracing, repair, prevention. van Doorn, R., (2012): “Bow thruster currents at open quay constructions on piles ”, Delft University of Technology, MSc thesis. Van Herpen, J.A. (1985): “The use of asphalt in hydraulic engineering ”, TAW Rijkswaterstaat. Van Manen, J.D. (1956): “Recent research on propellers in nozzles ”, NSP, Publication 136, Wageningen, The Netherlands. Van Manen, J.D. (1958): “Fundamentals of ship resistance and propulsion, part B: propulsion ”, SP, Publication 132a, Wageningen, The Netherlands. Verheij, H.J., (1983): “The stability of bottom and banks subjected to the velocities in the propeller  jet behind ships ”, 8th Int. Harbour Congress, Antwerp. 128

Verheij, H.J. en Stolker, C. (2007): “Hydro jets of fast ferries require proper designed quay walls ”, 2nd International Maritime-Port Technology and Development Conference, Singapore. Verheij, H.J., Stolker, C. en Groenveld, R. (2008): “Inland Waterways ”, Lecture notes VSSD, Delft. Verheij, H.J. (2010): “Comparison of water jets and conventional propeller jets ”, TU Delft, Delft. Verheij, H.J. (2010): “Nieuwe formules voor predictie schroefvermogens hoofdschroeven en boegschroeven van schepen in de binnenvaart ”. Wallenius Wilhelmsen, Green flagship, http://www.2wglobal.com/www/pdf/Green_Flagship.pdf (consulted 15/03/2010). Wellicome, J.F. (1981): “Bottom suction loads due to propeller scour action and ship movements ”, University of Southampton, Department of ship science. Wolfson Unit (2003): “CFD Investigation on the Bed Loads from a Water jet ”, Report 2413 prepared for Proserve Ltd. Wolfson Unit (2013): “CFD Investigations of Deflection Bucket Jet Flows and the Bed Scouring Loads Produced by RoRo Fast Ferries ”, Report 2442 prepared for Proserve Ltd. Yuksel, A., Celikoglu, Y., Cevik, E., Yuksel, Y. (2005): “Jet scour around vertical piles and pile groups”, Ocean engineering, 32, pp 349-362. Zanke, U. (2003): “On the influence of turbulence on the initiation of sediment motion ”, Int. Journal of Sediment Research, Vol. 18, No. 1, 2003, pp. 17-31.

129

ANNEX A. DEFINITIONS AND SYMBOLS  A

[m2]

Cross section

B

[1]

Stability coefficient

Bcr 

[1]

Critical Stability coefficient of the bed material

Bs

[m]

Beam = ship width

D

[m]

Diameter

Dthruster  [m]

Diameter thruster

D0

[m]

Effective diameter of a jet

DP

[m]

Diameter main propeller

D50

[m]

Diameter bed material; 50 % passing median stone diameter

E

[1]

Factor characterising the shape of the stern and the rudder configuration

E0

[J]

Energy flow in the initial cross section

F

[N]

Flow force

Fr

[1]

Froude number v / (g  h)0,5

Fr*

[1]

Froude number for non-cohesive bed material

Fr 0

[1]

Densimetric Froude number

PD

[W]

Maximum installed engine power

Pmain

[W]

Installed power for the main propulsion system

Pthruster  [W]

Installed power for the thruster

Q

[m3/s]

Discharge

R

[m/s]

Resistance

Re

[1]

Reynolds number (v  h / )

Re*

[1]

Reynolds number near the bed v * d / )

Re*

[1]

Reynolds number for bed material (v g d / )

T

[kN]

Thrust force

T

[m]

Ship’s draugth

S

[m]

Depth of a scour hole

S

[m/s]

Surcharge

V

[m3]

Volume

Va

[m/s]

Inflow velocity upstream of the propeller

Vcr 

[m/s]

Flow velocity at incipient motion

Vm

[m/s]

Average flow velocity

Vcrit

[m/s]

Critical flow velocity

Vx

[m/s]

Flow velocity in x direction

!

!

!

 A-3

v *2 / (ρ`  g  d)

V0

[m/s]

Induced flow velocity

Vmax

[m/s]

Maximum flow velocity in the flow direction

Vaverage

[m/s]

Average flow velocity in the flow direction

Vbed

[m/s]

Flow velocity near the bed

Vbed, cr   [m/s]

Critical flow velocity ‘near the bed’

Vbed, max [m/s]

Maximum flow velocity ‘near the bed’

Vs

Vessel speed

[m/s]

Vmax, So [m/s]

Maximum flow velocity near the bed

Vx, r 

[m/s]

Flow velocity in the jet at a distance x from the propeller and a distance r from the jet axis

V*

[m/s]

Shear velocity

WL

[1]

Water level

b

[1]

Roughness

f P

[-]

Percentage of installed engine power

b

[m]

Jet width

g

[m/s2]

Gravity constant

h

[m]

Water depth

hkeel

[m]

Keel clearance

hp

[m]

Height of the main propeller axis above the bed

hthruster 

[m]

Height of the thruster axis above the bed

kT

[1]

Thrust coefficient

kT,P

[1]

Thrust coefficient for a propeller in a nozzle

n

[1/s]

Number of revolutions of the propeller

r

[m]

Radial distance to the propeller jet axis

t

[s]

Time

xthruster 

[m]

Distance between outflow opening and quay wall

x

[m]

Horizontal distance to the propeller

x0

[m]

Length of the core zone

Δ

[-]

Relative buoyant density (ρs –ρw)/ρw

 A-4

ANNEX B. DIMENSIONS OF SHIPS Some graphs with respect to the main dimensions of ships are presented in the following Figures (based upon data from Lloyds Register of Ships and the sources). For further information we refer to the Guidelines of PIANC MarCom Working Group 49  – ‘Horizontal and vertical dimensions of fairways’  (PIANC, 2014, report 121) and to ROM.

Principal dimensions of general cargo ships

B-5

50

45

40

35

   ) 30   m    (    D    d   n   a    B  ,    ) 25   m    0    1    (    L

20

15

10

5

0 0

20

40

60

80

capacity (1000 dwt)

Principal dimensions of container vessels

B-6

100

120

70

60

50

   )   m    ( 40    D    d   n   a    B  ,    )   m    0    1    (    L

30

20

=

expected dimensions of bulk carrier in 2020 (Lloyd's Register)

10

0 0

50

100

150

200

250

300

capacity (1000 dwt)

Principal dimensions of bulk carriers

B-7

350

400

30

25

20

   )   m    (    D    d   n 15   a    B    )   m    0    1    (    L

10

5

0 0

5

10

15

20

capacity (1000 dwt)

Principal dimensions of tankers

B-8

25

30

80

70

60

50

40    )   m   n    i    (    D    d   n   a    B  ,    )   m    0    1    (    L

30

20

10

0 0

100

200

300

400

capacity (1000 dwt)

Principal dimensions of tankers > 40,000 dwt

B-9

500

600

AVERAGE DIMENSIONS OF FULLY LOADED SHIPS 10

Dead Weight Tonnes (DWT) [t]

Displacement (Δ)[t]

Length Overall (L) [m]

Length between Perpendiculars (Lpp) [m]

Beam (B) [m]

Depth (T) [m]

Draft (D) [m]

Block Coefficient

30.5 29.2 28.0

24.0 23.0 22.0

0.86 0.85 0.85

27.0 26.3 25.5 24.8 24.0

21.0 20.5 19.9 19.3 18.5

0.84 0.83 0.83 0.82

23.0 22.0 21.0 19.8 18.7 18.2 17.0

17.7 16.9 16.0 15.1 14.0 13.5 13.0

Tankers ULCC (Crude) 500,000 400,000

590,000 475,000

380.0

392.0 358.0

73.0 68.0

350,000

420,000

365.0

345.0

65.5

415.0

Tankers VLCC (Crude) 300,000 275,000 250,000 225,000 200,000

365,000 335,000 305,000 277,000 246,000

350.0 340.0 330.0 320.0 310.0

330.0 321.0 312.0 303.0 294.0

63.0 31.0 59.0 57.0 55.0

0.84

Tankers (Crude) 175,000 150,000

125,000 100,000 80,000 70,000 60,000

217,000 186,000 156,000 125,000 102,000 90,000 78,000

300.0 285.0 270.0 250.0 235.0

225.0 217.0

285.0 270.0 255.0 236.0 223.0 213.0 206.0

52.5 49.5 46.5 43.0 40.0 38.0

36.0

0.82 0.82

0.82 0.82 0.82 0.82 0.81

Tankers (Refined Oil Products) and Chemical Carriers 50,000 40,000 30,000 20,000 10,000 5,000 3,000

66,000 54,000 42,000 29,000 15,000 8,000 4,900

210.0 200.0

188.0 174.0 145.0 110.0

90.0

200.0 190.0 178.0 165.0 137.0 104.0 85.0

32.2 30.0 28.0 24.5 19.0 15.0 13.0

0.81

16.4 15.4 14.2 12.6 10.0 8.6 7.2

12.6 11.8 7.8 7.0 6.0

0.80 0.78 0.73 0.74 0.73 0.74

30.6 29.3 28.1 26.5 25.0 23.3 22.1 20.8 19.4 18.2 16.3 12.6 10.0

24.0 23.0 21.8 20.5 19.0 17.5 16.5 15.3 14.0 12.8 11.5 9.3 7.5

0.87 0.87 0.86 0.85 0.85 0.84 0.84 0.84 0.84 0.82 0.80 0.78 0.78

10.8 9.8

Dry Bulk and Polivalents 400,000 350,000 300,000 250,000 200,000 150,000 125,000 100,000 80,000 60,000 40,000 20,000 10,000

10 Based

464,000 406,000 350,000 292,000 236,000 179,000 150,000 121,000 98,000 74,000 50,000 26,000 13,000

375.0 362.0 350.0 335.0 315.0 290.0 275.0 255.0 240.0 220.0 195.0 160.0 130.0

356.0 344.0 333.0 318.0 300.0 276.0 262.0 242.0 228.0 210.0 185.0 152.0 124.0

on ROM (2000).

B-10

62.5 59.0 56.0 52.5 48.5 44.0 41.5 39.0 36.5 33.5 29.0 23.5 18.0

AVERAGE DIMENSIONS OF FULLY LOADED SHIPS

Dead Weight Tonnes (DWT) [t]

Displacement (Δ)[t]

Length Overall (L) [m]

Length between Perpendiculars (Lpp) [m]

Beam (B) [m]

Depth (T) [m]

Draft (D) [m]

Block Coefficient

26.1 22.3 17.8

11.3 10.5 9.7

0.64 0.62 0.54

12.0 12.0 11.8 11.4 9.5 9.2

0.78 0.76 0.76 0.73 0.74 0.74

11.5 11.3 10.6

0.74 0.78 0.69

13.5 12.9 12.3 11.2 10.6 9.3 8.1 7.0

0.68 0.67 0.65 0.62 0.59 0.57 0.54 0.54

Methan Gas Carriers 60,000 40,000 20,000

88,000 59,000 31,000

290.0 252.0 209.0

275.0 237.0 199.0

44.5 38.2 30.0

LNG Carriers (Prismatic) 125,000 97,000 90,000 80,000 52,000 27,000

175,000 141,000 120,000 100,000 58,000 40,000

345.0 315.0 298.0 280.0 247.3 207.8

333.0 303.0 285.0 268.8 231.0 196.0

55.0 50.0 46.0 43.4 34.8 29.3

LNG Carriers (Sferes, Moss) 75,000 58,000 51,000

117,000 99,000 71,000

288.0 274.0 249.5

274.0 262.0 237.0

49.0 42.0 40.0

LPG Carriers 60,000 50,000 40,000 30,000 20,000 10,000 5,000 3,000

95,000 80,000 65,000 49,000 33,000 17,000 8,800 5,500

265.0 248.0 240.0 226.0 207.0 160.0 134.0 116.0

245.0 238.0 230.0 216.0 197.0 152.0 126.0 110.0

B-11

42.2 39.0 35.2 32.4 26.8 21.1 16.0 13.3

23.7 23.0 20.8 19.9 18.4 15.2 12.5 10.1

AVERAGE DIMENSIONS OF FULLY LOADED SHIPS

Dead Weight Tonnes (DWT) [t]

Displacement (Δ)[t]

Length Overall (L) [m]

Length between Perpendiculars (Lpp) [m]

Beam (B) [m]

Depth (T) [m]

Draft (D) [m]

Block Coefficient

TEU

23.6 23.2 22.8 22.4

18.0 16.5 16.0 15.0 15.0 14.8 14.5 14.5 14.5 14.5 13.8 13.5 13.2 12.8

0.69 0.68 0.68 0.66 0.70 0.68 0.70 0.71 0.66 0.66 0.65 0.64 0.63 0.63

22000 18000 14500 12200 10000 9000 8000 7500 7000 6500 6000 5600 5200 4800

22.8 22.4 22.1 21.4 20.4 19.3 18.5 17.5 16.2 15.0 13.3

13.2 12.8 12.5 12.2 11.7 11.1 10.7 10.1 9.2 8.5 7.3

0.71 0.69 0.67 0.64 0.64 0.63 0.63 0.63 0.68 0.69 0.70

5000 4500 4000 3500 3000 2600 2200 1800 1500 1100 750

Containerships (Post-Panamax) 245,000 200,000 195,000 165,000 125,000 120,000 110,000 100,000 90,000 80,000 70,000 65,000 60,000 55,000

340,000 260,000 250,000 215,000 174,000 158,000 145,000 140,000 126,000 112,000 100,000 92,000 84,000 76,500

470.0 400.0 418.0 398.0 370.0 352.0 340.0 326.0 313.0 300.0 280.0 274.0 268.0 261.0

446.0 385.0 395.0 376.0 351.0 335.0 323.0 310.0 298.0 284.0 266.0 260.0 255.0 248.0

60.0 59.0 56.4 56.4 45.8 45.6 43.2 42.8 42.8 40.3 41.8 41.2 39.8 38.3

Containerships (Panamax) 60,000 55,000 50,000 45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000

83,000 75,500 68,000 61,000 54,000 47,500 40,500 33,500 27,000 20,000 13,500

290.0 278.0 267.0 255.0 237.0 222.0 210.0 195.0 174.0 152.0 130.0

275.0 264.0 253.0 242.0 225.0 211.0 200.0 185.0 165.0 144.0 124.0

32.2 32.2 32.2 32.2 32.2 32.2 30.0 28.5 26.2 23.7 21.2

B-12

AVERAGE DIMENSIONS OF FULLY LOADED SHIPS

Dead Weight Tonnes (DWT) [t]

Displacement (Δ)[t]

Length Overall (L) [m]

Length between Perpendiculars (Lpp) [m]

Beam (B) [m]

Depth (T) [m]

Draft (D) [m]

Block Coefficient

Ro/Ro Ships 50,000 45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000

87,500 81,500 72,000 63,000 54,000 45,000 36,000 27,500 18,400 9,500

287.0 275.0 260.0 245.0 231.0 216.0 197.0 177.0 153.0 121.0

273.0 261.0 247.0 233.0 219.0 205.0 187.0 168.0 145.0 115.0

CEU

32.2 32.2 32.2 32.2 32.0 31.0 28.6 26.2 23.4 19.3

28.5 27.6 26.2 24.8 23.5 22.0 21.0 19.2 17.0 13.8

12.4 12.0 11.4 10.8 10.2 9.6 9.1 8.4 7.4 6.0

0.80 0.80 0.79 0.78 0.75 0.75 0.75 0.74 0.73 0.71

30.0 28.9 27.7 26.4 24.8 22.6 19.8 15.8 13.0

18.0 17.0 16.0 15.4 13.8 12.8 11.2 8.5 6.8

12.5 12.0 11.3 10.7 10.0 9.2 8.0 5.4 5.0

0.73 0.73 0.73 0.72 0.71 0.71 0.72 0.74 0.77

5000 4500 4000 3500 3000 2500 2000 1500 1000 600

Cargo 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 2,500

54,500 48,000 41,000 34,500 28,000 21,500 14,500 7,500 4,000

209.0 199.0 188.0 178.0 166.0 152.0 133.0 105.0 85.0

199.0 189.0 179.0 169.0 158.0 145.0 127.0 100.0 80.0 Car Carriers

70,000 65,000 57,000 45,000 36,000 27,000 18,000 13,000 8,000

52,000 48,000 42,000 35,500 28,500 22,000 13,500 8,000 4,300

228.0 220.0 205.0 198.0 190.0 175.0 150.0 130.0 100.0

210.0 205.0 189.0 182.0 175.0 167.0 143.0 124.0 95.0

CEU 32.2 32.2 32.2 32.2 32.2 28.0 22.7 18.8 17.0

11.3 11.0 10.9 10.0 9.0 8.4 7.4 6.2 4.9

0.66 0.64 0.62 0.59 0.55 0.55 0.55 0.54 0.53

8.2 9.0 3.7 7.9 5.5 5.2 5.4 3.5 4.2 2.6

0.65 0.48 0.80 0.49 0.58 0.51 0.73 0.58 0.47 0.46

Military Ships 16,000 (1) 15,000 (2) 5,000 (3) 4,000 (4) 3,500 (5) 1,500 (6) 1,500 (7) 1,400 (8) 750 (9) 400 (10)

20,000 19,000 5,700 7,000 4,600 2,100 1,800 1,800 1,000 500

172.0 195.0 117.0 134.0 120.0 90.0 68.0 89.0 52.0 58.0

163.0 185.0 115.0 127.0 115.0 85.0 67.0 85.0 49.0 55.1

B-13

23.0 24.0 16.8 14.3 12.5 9.3 6.8 10.5 10.4 7.6

. . . . . . . . . .

8000 7000 6000 5000 4000 3000 2000 1000 700

AVERAGE DIMENSIONS OF FULLY LOADED SHIPS

Dead Weight Tonnes (DWT) [t]

Displacement (Δ)[t]

Length Overall (L) [m]

Length between Perpendiculars (Lpp) [m]

Beam (B) [m]

Depth (T) [m]

Draft (D) [m]

Block Coefficient

41.6 39.0 36.4 32.8 30.6 28.7 27.6 26.5 25.3 24.1 23.5 22.7 21.6 19.0 17.1 14.6

10.3 9.8 8.8 7.8 7.1 6.7 6.5 6.3 6.1 5.9 5.8 5.6 5.4 4.7 4.1 3.3

0.65 0.65 0.65 0.63 0.61 0.61 0.61 0.61 0.60 0.59 0.58 0.56 0.58 0.57 0.56 0.54

30.5 26.5 24.7 24.0 21.2 16.7 13.8 11.6

4.3 3.7 3.4 3.2 3.1 2.1 1.8 1.6

0.43 0.43 0.43 0.42 0.39 0.37 0.35 0.35

8.2 9.0 3.7 7.9 5.5 5.2 5.4 3.5 4.2 2.6

0.65 0.48 0.80 0.49 0.58 0.51 0.73 0.58 0.47 0.46

Ferries 50,000 40,000 30,000 20,000 15,000 12,500 11,500 10,200 9,000 8,000 7,000 6,500 5,000 3,000 2,000 1,000

82,500 66,800 50,300 33,800 25,000 21,000 19,000 17,000 15,000 13,000 12,000 10,500 8,600 5,300 3,500 1,800

309.0 281.0 253.0 219.0 197.0 187.0 182.0 175.0 170.0 164.0 161.0 155.0 133.0 110.0 95.0 74.0

291.0 264.0 237.0 204.0 183.0 174.0 169.0 163.0 158.0 152.0 149.0 144.0 124.0 102.0 87.0 68.0 Fast Ferries (Multihull)

9,000 6,000 5,000 4,000 2,000 1,000 500 250

3,200 2,100 1,700 1,400 700 350 175 95

127.0 107.0 97.0 92.0 85.0 65.0 46.0 42.0

117.0 93.0 83.0 79.0 77.0 62.0 41.0 37.0 Military Ships

16,000 (1) 15,000 (2) 5,000 (3) 4,000 (4) 3,500 (5) 1,500 (6) 1,500 (7) 1,400 (8) 750 (9) 400 (10)

20,000 19,000 5,700 7,000 4,600 2,100 1,800 1,800 1,000 500

Comments (1) Carrier (2)  Aircraft Carrier (3) Landing Craft

172.0 195.0 117.0 134.0 120.0 90.0 68.0 89.0 52.0 58.0 (4) (5) (6)

163.0 185.0 115.0 127.0 115.0 85.0 67.0 85.0 49.0 55.1

Missil Frigate Destroyer Fast Frigate

23.0 24.0 16.8 14.3 12.5 9.3 6.8 10.5 10.4 7.6 (7) (8) (9)

B-14

Submarin Corbet Miner Ship

. . . . . . . . . . (10)

Patrol

AVERAGE DIMENSIONS OF FULLY LOADED SHIPS

Dead Weight Tonnes (DWT) [t]

Displacement (Δ)[t]

Length Overall (L) [m]

Length between Perpendiculars (Lpp) [m]

Beam (B) [m]

Depth (T) [m]

Draft (D) [m]

Block Coefficient

9.2 9.0 8.8 8.6 8.5 8.3 8.0

0.67 0.66 0.67 0.66 0.67 0.67 0.66

8.0 7.9 7.8 7.6 7.6 7.1 7.4 6.5 7.0 6.3 6.8 6.7 6.6 6.5 6.4 5.8 5.6

0.67 0.66 0.66 0.63 0.65 0.62 0.64 0.62 0.64 0.62 0.61 0.61 0.60 0.60 0.60 0.59 0.59

Cruise Liners (Post-Panamax)

Esto es GT, no DWT

220,000 160,000 135,000 115,000 105,000 95,000 80,000

118,000 84,000 71,000 61,000 56,000 51,000 44,000

360.0 339.0 333.0 313.4 294.0 295.0 272.0

333.0 316.6 308.0 290.0 272.0 273.0 231.0

55.0 43.7 37.9 36.0 35.0 33.0 35.0

Cruise Liners (Panamax) 90,000 80,000 70,000 60,000 60,000 50,000 50,000 40,000 40,000 35,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000

48,000 43,000 38,000 34,000 34,000 29,000 29,000 24,000 24,000 21,000 21,000 18,200 16,200 14,000 11,500 8,000 5,000

294.0 280.0 265.0 252.0 251.2 234.0 232.0 212.0 210.0 192.0 205.0 190.0 180.0 169.0 152.0 134.0 100.0

272.0 248.7 225.0 214.0 232.4 199.0 212.0 180.0 192.8 164.0 188.0 175.0 165.0 155.0 140.0 123.0 90.0

32.2 32.2 32.2 32.2 28.8 32.2 28.0 32.2 27.1 32.0 26.3 25.0 24.0 22.5 21.0 18.5 16.5

Fishing Boats 3,000 2,500 2,000 1,500 1,200 1,000 700 500

4,200 3,500 2,700 2,200 1,900 1,600 1,250 800

90.0 85.0 80.0 76.0 72.0 70.0 65.0 55.0

85.0 81.0 76.0 72.0 68.0 66.0 62.0 53.0

14.0 13.0 12.0 11.3 11.0 10.5 10.0 8.6

6.8 6.4 6.0 5.8 5.7 5.4 5.1 4.5

5.9 5.6 5.3 5.1 5.0 4.8 4.5 4.0

0.60 0.59 0.56 0.53 0.50 0.48 0.45 0.44

250

400

40.0

38.0

7.0

4.0

3.5

0.43

B-15

Motor Boats 50,0 35,0 27,0 16,5 6,5 4,5 1,3

24.0 21.0 18.0 15.0 12.0 9.0 6.0

.

......

5.5 5.0 4.4 4.0 3.4 2.7 2.1

.

......

3.3 3.0 2.7 2.3 1.8 1.5 1.0

.

......

Sailing Boats 60,0 40,0 22,0 13,0 10,0 3,5 1,5

24.0 21.0 18.0 15.0 12.0 9.0 6.0

. ..... .

4.6 4.3 4.0 3.7 3.5 3.3 2.4

. ..... .

3.6 3.0 2.7 2.4 2.1 1.8 1.5

. ..... .

Comments (1) Indicated Beam is Max Beam taken at the level of superstructure. Effective Beam on water level line is about 45/50 % of Max Beam. (2) Water Line Beam is about 80/90 % of beam indicated that is Max Beam at the level of super structure. (3)

Indicated Draft is when no or slow sailing and no stabilisers. On fast navigation with stabilisers add about 70/80 %.

(4)

Block Coefficient is calculated with Effective Beam at water line level.

B-16

ANNEX C. DAMAGES  – QUESTIONNAIRE C.1 

USA (Marcel Hermans):    



 

 

       

Huelva: P. G. Navarro – Projects and Works Department (+34.959.49.31.00, [email protected] ) Bilbao: M. J. Hernàez – Projects and Works Department (+34.94.487.12.00, [email protected] ) Castellon: A. Velasco – Infrastructures Department (+34.964.281.140, [email protected] ) Cartagena: J. Cebrian – Infrastructures Department (+34.968.325.809, [email protected]) Ferrol: I. de la Pena –Investments & Planning Department (+34.981.338.000, [email protected] ) Marin y Ria de Pontevedra: F. Linaje – Projects & Works Department (+34.986.855.200, [email protected]) Puertos del Estado Madrid: J.I. Grau – Subdirector Infrastructure (+91.524.55.00,  [email protected]) Santander: J.L. Zatarain – Director Infrastructure (+34.942.203.600, [email protected] ) Tenerife: J.I. Mora – Head Infrastructure Department ( +34.922.605.448,  [email protected])

THE NETHERLANDS (Henk Verheij)  



Boulogne-Calais: D. Lepers – Infrastructure Division (+33.3.21.00.68.30, [email protected] ) Dunkerke: F. Caron – Infrastructure division ([email protected] ) Le Havre: C. Bénard – Infrastructure division (+33.2.32.74.74.66, [email protected] )

SPAIN (José Luis Zatarain): 



Antwerpen: T. van Autgaerden (+32.3.205.25.69, [email protected] ) Gent: K. Lamers –Technical Division (+32.9.521.05.50) Zeebrugge & Oostende: L. Van Damme (+32.59.55.42.16, [email protected] )

FRANCE (Marc Sas): 



Corpus Christi: G. Brubeck (361-885-6138) L.A: R. Aliviado – Engineering Division (310-732-3626) New York & New Jersey: T. Wakeman (973-792-4660), R. Kruidman, P.Jacobson (212435-4265) Portland: M. Hermans (503-415-6305)

BELGIUM (Marc Sas): 



C.1 Ports Participating to the Survey

IJmuiden : R. Van Velzen – Head Technical Department (+31.255.547000, [email protected] ) Rotterdam : J.G. de Gijt – Engineering Department Municipality Rotterdam,  [email protected]

GERMANY (Eckard Schmidt)    

Niedersachsen Ports : H.-J. Uhlendorf, (+49.441/799.22.37, [email protected] ) Bremenports consult GmbH : Hans-Werner Vollstedt, (+49.471/596.13.103, [email protected]) Fährhafen Sassnitz : Arnim Jagow (+49.38392/55.215, [email protected]) Hafenentwicklungsgesellschaft Rostock : Jörg Heinze (+49.381/35.05.110,  [email protected]) C-17



NORWAY (Carl Thoresen)      

C.2

Oslo: P. Halvorsen – Technical director (+4702180, [email protected] ) Borg: T. Lundestad – Technical Director (+4769358900, [email protected] ) Drammen: R. Kristiansen  –Technical Director (+4732208650, [email protected] ) Larvik: J.F. Jonas – Port Director (+4733165750, [email protected]) Kristiansand: S.-I. Larsen – Technical Director (+4738006004, [email protected] ) Bergen: T. Bjerkli – Technical director (+4755568950, [email protected] )

Summary of the Answers

C.2.1. Situation 

Has your port experienced any scour damage at its structures?

 Almost all surveyed port experienced scour damage without actually knowing whether caused by main or bow thrusters. New York-New Jersey (pile supported decks above riprap slope), Bilbao, Castellon and Pontevedra didn’t experience any damage. Only in Dunker  que could damage clearly be linked to bow thrusters. And in Corpus Christi, where 2-3 tugs are used for (de-)mooring, scour is due to tugs prop wash. 

Have you taken measures to limit or avoid scour damage?

 All ports where scour damage has been experienced took measures or are planning to. Some reacted with emergency curative backfilling of the scours and the holes in riprap. Others undertook light to heavy structural measures (geotextile, rat-proofing, concrete mat, riprap, secondary sheet piles protecting the main ones). 

Has scour protection been an issue at any recent berth design?

 All ports where new berths were recently built included scour problem in the design, sometimes combined with other issues (in L.A. for instance, flatter slopes for seismic issue also reduces scouring) 

Do you know of others (companies/ports) in your area that deal with scour issues?

Problem is generally felt as a global issue. 

Describe situation where you experience scour damage/issue. (Vessel types, berth structure type, water level/ underkeel clearance, sediment type, (de)berthing procedures/tug-use, frequency of use, etc.

Scours are detected for several structures in sandy bottom (slopes under pile-supported structures, foundation of vertical sheet pile cells, diaphragm, gravity, kombi and dam walls). Erosion of riprap blocks and sinkholes behind 2-D concrete protection has also been detected. On some places important scours were clearly located near usual location of bow thrusters. Quoted type of ships are container vessels, ferries and Ro/Ro ships. High frequency and low keel clearance seem to be worsening factors. 

What are your main concerns related to the scour issue? (berth structure stability/damage, sediment distribution/ dredging need, environmental, other?)

 Almost everywhere is berth stability the main concern and the increase of dredging needs by displacement of sediments an important linked issue. Environmental concerns where never quoted. As all the investigated people are responsible for the infrastructure, their job is to be concerned about the structure stability!

C-18



What are in your mind or experience the main factors contributing to the extent of scouring for your specific situation? In other words, what factor(s) do you see as the main variable(s) in actual scour impacts at your berths?    

Concentration of bow thrusters in same spot and use of it at full power (always necessary?) Low underkeel clearance (type of ships, loading rates) Ships power and berthing frequency Type of structure and sediments  – wrong design

C.2.2. Monitoring/Studies 

How often do you monitor?

Generally on a fixed frequency (from once every two months to once a year) and upon demand or depending on the progress of the damages. 

What monitoring method is used?

Bathymetric, multi-beams, divers, plumb line, etc. 

How do you plan any decisions/ follow up of monitoring results?

Generally bathymetric survey on a fixed frequency, if problems detected divers for further investigation, curative-structural solution where needed and follow up of the efficiency of the solution. 

Have you performed any studies or research related to this issue? 

Zeebrugge: Propeller velocity measured nearby the bottom (’90) Dunkerque: Risk analysis for reducing dock capacity depending on observed damages (planned)



Portland: Quantifying scour forces and hole depth, conceptual design solutions



C.2.3. Protective Measures 

Have you implemented any protective measures at any of your berths related to scour? What kind of measures have you used (structural, operational, …)? When were measures implemented and what kind of experience do you have with those measures?

Measure were always taken when problem occurred: 

Curative ones (Backfilling with sand rocky material, pumped concrete)



Structural ones (Riprap and concrete mattresses most of all, sheet pile in font of open structures)



Operational ones (Using less damaged docks in priority, thinking off new management policy)

Undertaken measures were generally strong enough for stopping the erosion but initial appropriate design seems more efficient. 

What were main factors in selection of measures? (or rate the following at a scale from 1 to 10: Application time, maintenance, durability, environmental restrictions, flexibility to future depth, cost, proven technology, availability, vessel/user requirements, ot her….)

From most to less frequently quoted : 

Proven technique

C-19



 

Availability

 

Maintenance

 

Cost



User requirements



Environmental, flexibility, execution time

Are there any restrictions in the use of engine Power during the (de)berthing manoeuvres?

Only in Portland temporary restrictions depending on under keel clearance and use of tugs. Thinking off taking such a measure in Antwerp. 

Do you have any record of used power/as compared to installed power) during the manoeuvres?

Nobody did. For such information, WG should contact captaincy, pilots, ships societies, etc. The Port of Rotterdam also should. C.2.4. Other 

Are there any data, reports, etc. that you could share for use by the PIANC WG?  





Ferrol: “Scour at marine structures" (Richard Whitehouse –  ISBN 0 7 277 2655 2 – Editorial Thomas Telford – year 1998). Portland, Antwerpen, Zeebrugge, Boulogne, Dunkerque, Le Havre, Tenerife told to be ready to communicate documents.

What other important or relevant issues do you experience or see related to this scour issue? 

Strong divergences between guidelines from EAU and PIANC for same characteristics.



Power characteristics of new generation container carriers still badly known, bow thrusters more and more frequently used.



Influence of structural protection on dredging options (with riprap it is no longer possible to use dredgers with a bucket).

Do you have any other concerns, tips, advice, or the like for the WG? 

Scour protection should be involved since the stage of design and not only when damages are observed.



All surveyed French ports insisted on the importance of the issue and wish to be kept informed on the results of the WG.

C-20