Guideline for Fuel Saving Measures on Bulk Carriers

With compliments of: Please attach SDARI or DNV business card before handing over to client

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Guideline for fuel saving measures, Rev. 1

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Background Shanghai Merchant Ship Design & Research Institute, CSSC (SDARI) and Det Norske Veritas AS (DNV) have worked together to provide guidance on relevant fuel saving measures for bulk carriers to be built in China. The aim is to help ship owners cut costs and reduce emissions. Studies report a large margin for savings, and there exists a variety of options on how to cut the required engine power. It is challenging to manoeuvre these waters, with various suppliers promoting their device claiming large savings at low costs. There is no doubt that the fuel consumption of a typical bulk carrier design with a standard propeller and rudder may be significantly reduced by use of current technology, and at a cost that implies a pay back time acceptable to most owners. Objective of the joint project: To provide to Ship Owners advice regarding available technology and cost effectiveness of Fuel Saving Measures which are relevant for Bulk Carriers to be built in China There are two main deliverables: • A guideline on fuel saving measures - this document • A framework for return-on-investment calculations for fuel saving measures The scope of the guideline is to provide an overview of the most relevant fuel saving measures that are available for bulk carriers to be built in China. It covers the following fuel saving measures: • Hull shape • Openings – arrangement and design • Mewis duct • Propeller nozzle • Pre duct • Pre-swirl stator • Propeller design • Contra rotating propeller • Propeller boss cap fin • Propeller rudder transition bulb • Rudder profile • Main engine • Auxiliary engine • Waste heat recovery system

© SDARI and DNV

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Table of contents 1. 2.

Introduction ................................................................................................................... 9 Physical descriptions of the fuel efficiency measures ................................................. 11 2.1 Resistance components ......................................................................................... 11 2.2 Propeller characteristics ........................................................................................ 12 2.3 Components around working propeller ................................................................ 13 3. General description of evaluation parameters ............................................................. 16 3.1.1 Description, including compatibility ............................................................. 16 3.1.2 Classification requirements ........................................................................... 16 3.1.3 Complexity of manufacturing ........................................................................ 16 3.1.4 Range of expected fuel savings ..................................................................... 16 3.1.5 Expected maintenance needs of device in operation ..................................... 17 3.1.6 Indication of price range ................................................................................ 17 4. Design and verification of fuel saving measures ......................................................... 18 4.1 Full scale measurements ....................................................................................... 18 4.2 Model tests ............................................................................................................ 19 4.3 Computational fluid dynamics (CFD) .................................................................. 19 5. Detailed evaluation of fuel saving measures ............................................................... 21 5.1 Hull shape ............................................................................................................. 21 5.1.1 Physical description ....................................................................................... 21 5.1.2 Requirements from classification .................................................................. 22 5.1.3 Complexity of manufacturing ........................................................................ 22 5.1.4 Range of expected fuel saving ....................................................................... 22 5.1.5 Expected maintenance needs ......................................................................... 22 5.1.6 Indication of price range ................................................................................ 23 5.2 Openings – Arrangement and design .................................................................... 24 5.2.1 Physical description ....................................................................................... 24 5.2.2 Requirements from classification .................................................................. 25 5.2.3 Complexity of manufacturing ........................................................................ 25 5.2.4 Range of expected fuel saving ....................................................................... 25 5.2.5 Expected maintenance needs ......................................................................... 25 5.2.6 Indication of price range ................................................................................ 25 5.3 Mewis Duct ........................................................................................................... 26 5.3.1 Physical description ....................................................................................... 26 5.3.2 Requirements from classification .................................................................. 28 5.3.3 Complexity of manufacturing ........................................................................ 28 5.3.4 Range of expected fuel saving ....................................................................... 29 5.3.5 Expected maintenance needs ......................................................................... 29 5.3.6 Indication of price range ................................................................................ 29 5.4 Propeller nozzle .................................................................................................... 30 5.4.1 Physical description ....................................................................................... 30 5.4.2 Requirements from classification .................................................................. 30 5.4.3 Complexity of manufacturing ........................................................................ 30 5.4.4 Range of expected fuel saving ....................................................................... 31 5.4.5 Expected maintenance needs ......................................................................... 31 5.4.6 Indication of price range ................................................................................ 32 5.5 Pre duct ................................................................................................................. 33 Page 4 of 84


5.5.1 Physical description ....................................................................................... 33 5.5.2 Requirements from classification .................................................................. 34 5.5.3 Range of expected fuel saving ....................................................................... 34 5.5.4 Expected maintenance needs ......................................................................... 34 5.5.5 Indication of price range ................................................................................ 34 5.6 Pre-swirl stator ...................................................................................................... 35 5.6.1 Physical description ....................................................................................... 35 5.6.2 Requirements from classification .................................................................. 36 5.6.3 Complexity of manufacturing ........................................................................ 36 5.6.4 Range of expected fuel saving ....................................................................... 36 5.6.5 Expected maintenance needs ......................................................................... 36 5.6.6 Indication of price range ................................................................................ 37 5.7 Propeller design .................................................................................................... 39 5.7.1 Physical description ....................................................................................... 39 5.7.2 Requirements from classification .................................................................. 40 5.7.3 Complexity of manufacturing ........................................................................ 40 5.7.4 Range of expected fuel saving ....................................................................... 41 5.7.5 Expected maintenance needs ......................................................................... 41 5.7.6 Indication of price range ................................................................................ 41 5.8 Contra rotating propeller ....................................................................................... 42 5.8.1 Physical description ....................................................................................... 42 5.8.2 Requirements from classification .................................................................. 42 5.8.3 Complexity of manufacturing ........................................................................ 42 5.8.4 Range of expected fuel saving ....................................................................... 43 5.8.5 Expected maintenance needs ......................................................................... 44 5.8.6 Indication of price range ................................................................................ 44 5.9 Propeller Boss Cap Fins and Propeller Cap Turbines ........................................... 45 5.9.1 Physical description ....................................................................................... 45 5.9.2 Requirements from classification .................................................................. 46 5.9.3 Complexity of manufacturing ........................................................................ 46 5.9.4 Range of expected fuel saving ....................................................................... 46 5.9.5 Expected maintenance needs ......................................................................... 46 5.9.6 Indication of price range ................................................................................ 47 5.10 Propeller rudder transition bulb......................................................................... 48 5.10.1 Physical description ....................................................................................... 49 5.10.2 Requirements from classification .................................................................. 49 5.10.3 Complexity of manufacturing ........................................................................ 49 5.10.4 Range of expected fuel saving ....................................................................... 50 5.10.5 Expected maintenance needs ......................................................................... 50 5.10.6 Indication of price range ................................................................................ 50 5.11 Rudder profile ................................................................................................... 51 5.11.1 Physical description ....................................................................................... 51 5.11.2 Requirements from classification .................................................................. 52 5.11.3 Complexity of manufacturing ........................................................................ 52 5.11.4 Range of expected fuel saving ....................................................................... 52 5.11.5 Expected maintenance needs ......................................................................... 52 5.11.6 Indication of price range ................................................................................ 52 5.12 Main engine ....................................................................................................... 53

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5.12.1 Physical description ....................................................................................... 53 5.12.2 De-rating of main engine ............................................................................... 53 5.12.3 Use of electronically controlled engine for engine control tuning ................ 54 5.12.4 Part load or low load optimization by use of variable turbine area or exhaust gas bypass .................................................................................................................... 55 5.12.5 Requirements from classification .................................................................. 57 5.13 Auxiliary engine ................................................................................................ 58 5.13.1 Physical description ....................................................................................... 58 5.13.2 Requirements from classification .................................................................. 58 5.13.3 Range of expected fuel savings ..................................................................... 58 5.14 Waste heat recovery system .............................................................................. 59 5.14.1 Physical description ....................................................................................... 59 5.14.2 Requirements from classification .................................................................. 60 5.14.3 Range of expected fuel savings ..................................................................... 60 6. Comparison of fuel saving measures including compatibility .................................... 61 7. References ................................................................................................................... 63 8. Disclaimer .................................................................................................................... 64

Appendices: 1.

User Guide ................................................................................................................... 66 1.1 General .................................................................................................................. 66 1.2 Content .................................................................................................................. 66 1.2.1 Workbook protection and macros.................................................................. 67 1.2.2 Tips and notes ................................................................................................ 67 1.2.3 Print ............................................................................................................... 67 1.3 Guidelines ............................................................................................................. 68 1.3.1 Project data .................................................................................................... 68 1.3.2 Fuel saving measure ...................................................................................... 69 1.3.3 Operating profile............................................................................................ 70 1.3.4 Fuel price scenario ......................................................................................... 71 1.3.5 Cost benefit .................................................................................................... 71 1.3.6 Sensitivity analysis ........................................................................................ 73 1.3.7 Emissions ....................................................................................................... 74 1.3.8 Cash flows ..................................................................................................... 74

1.

Methodology ................................................................................................................ 77 1.1 Objective ............................................................................................................... 77 1.2 Assumptions .......................................................................................................... 77 1.3 Model .................................................................................................................... 77 1.3.1 Fuel saving measure & estimated costs ......................................................... 78 1.3.2 Operating profile & fuel consumption........................................................... 78 1.3.3 Financial scenario & fuel price development ................................................ 78 1.3.4 Fuel savings and cost-benefit of fuel saving measure ................................... 78 1.3.5 Sensitivity ...................................................................................................... 79

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2.

Financial METRICS .................................................................................................... 80 2.1.1 Return on investment ..................................................................................... 80 2.1.2 Net Present Value (NPV) .............................................................................. 81 2.1.3 Internal Rate of Return (IRR) ........................................................................ 81 2.1.4 Payback period .............................................................................................. 82 2.1.5 Profitability index .......................................................................................... 82

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List of figures Figure 1 Overview of nomenclature used in ship resistance and propulsion. From MAN B&W “Basic Principles of Ship Propulsion” /21/. .............................................................. 14 Figure 2 Typical sources of energy loss for a working propeller. From Mewis and Hollenbach /4/...................................................................................................................... 15 Figure 3 Possible power reduction including the Mewis Duct. From /1/. ........................... 17 Figure 4 Examples of some openings designs, courtesy of HSVA. .................................... 24 Figure 5 Installed Mewis Duct on Grieg I-class vessel. From /1/. ...................................... 26 Figure 6 CFD plots in plane after Mewis duct and before propeller. Courtesy of Becker Marine Systems. From /30/. ................................................................................................ 27 Figure 7 Illustration of possible increase in propulsive efficiency by use of a propeller nozzle. From /16/. ................................................................................................................ 31 Figure 8 Schneekluth WED, courtesy of Schneekluth ........................................................ 33 Figure 9 Pre-swirl stator. Courtesy of DSME. .................................................................... 35 Figure 10. Contra rotating propeller from Mitsubishi Heavy Industries, LTD ................... 42 Figure 11 IHMU CRP system on diesel-electric driven vessels ......................................... 43 Figure 12 Propeller boss cap fins. From /1/ and /2/............................................................. 45 Figure 13 Propeller rudder transition bulb. Courtesy of DSME. ......................................... 48 Figure 14 Costa bulb. From /24/. ......................................................................................... 48 Figure 15 PROMAS integrated propulsion manoeuvring system. Courtesy of Rolls-Royce Marine. ................................................................................................................................. 49 Figure 16 Different standard rudder profiles. From /26/. .................................................... 51 Figure 17 Relative fuel consumption in normal service of different derated main engines for a 75,000 dwt Panamax product tanker at 15 knots. From /22/. ..................................... 54 Figure 18 Example of SFOC reductions for a MAN B&W 6S80ME-C8.2 with ECT. From /31/. ...................................................................................................................................... 55 Figure 19 Example of benefits of variable turbine (VT) for electronically controlled engines. From /31/. .............................................................................................................. 56 Figure 20 Example of benefits of variable turbine (VT) for mechanically controlled engines. From /31/. .............................................................................................................. 56 Figure 21 Example of benefits of exhaust gas bypass (EGB). From /31/. .......................... 57 Figure 22 Power concept for a waste heat recovery system. From /32/. ............................. 59

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1.

Introduction

Typical bulk carrier designs with traditional propulsion systems have a significant potential for fuel saving. There is a current high focus on green ship designs, and owners would prefer to get an efficient vessel at little or no additional cost in a two-three year perspective. Various fuel saving measures are being promoted, with seemingly large saving potentials. Owners may experience to be bombarded with well meant offers of clever energy efficiency devices. However, the actual cost of installation and maintenance is often uncertain, and the advertised saving potential may be overly optimistic. SDARI and DNV have joined forces to address the need for an objective guide addressing various issues relative to fuel saving measures for bulk carriers to be built in China. The main goal is to facilitate implementation of measures to reduce emissions and assist in cost cutting in an extremely competitive bulk market. The price of fuel oil is high and rates are low. The guide includes a list of relevant fuel saving devices with typical ranges of expected fuel saving. These numbers originate from various sources; supplier data or owner’s estimates, based on e.g. model tests, full-scale measurements or Computational Fluid Dynamics (CFD) analyses. The cost side is equally important to assess the cost-benefit. Quotes from various suppliers are the basis for cost estimates included in this guide, in addition to expected costs based on actual manufacturing experience. Some cost values are also obtained from other published material. The guide includes a comprehensive list of references with appropriate links in the text. Maintenance cost is also important to consider. It is possible to perform a reasonably accurate return on investment analysis based on this guide. A Return of Investment tool is developed as part of this project, and it is available on request from SDARI and DNV. Compatibility between different fuel saving measures is discussed, based on a physical description on how the hydrodynamic flow is modified. Some devices may be combined to produce a total saving approaching the sum of savings from each device. Others may act together to increase the total fuel consumption instead of improving performance. Class requirements are also addressed in the guide. The guide’s focus is on fuel saving measures for new building vessels, but whether the fuel saving device is an option for retro-fit is discussed for some of the fuel saving devices. It is challenging to validate the savings and proper use of model tests, full-scale tests or CFD analyses may be required. The guide discusses validation in general, e.g. the value of a partial validation by looking at change in flow properties instead of only focussing on final speed-power results. This guide does not consider operational measures to reduce emissions and save fuel, although there is no doubt ship operation is an extremely important factor to reduce emissions and save fuel.

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Another important issue is the choice of basis for hull, engine and propulsion optimization. Traditionally, this has been kept simple by focussing on the design draft and design speed. Now there is a trend for ship owners to require a new vessel to perform over a range of drafts and speeds. The traditional bulk carrier is somewhat easy in that it trades mostly laden or in ballast, and the high block and low speed means that the calm water wave making resistance is not that important. Chapter 2 provides an introduction to the physics of ship propulsion and resistance and includes a description on how the various devices influence the flow to achieve a reduced required power. Chapter 3 consists of a general description of the evaluation parameters: 1. 2. 3. 4. 5. 6.

Description, including compatibility Requirements from Classification Complexity of manufacturing Range of expected fuel saving Expected maintenance needs of device in operation Rough Indication of price range

Chapter 4 covers design and verification of fuel saving devices. The bulk of this guide consists of Chapter 5, which discusses the fourteen different fuel saving measures with respect to the six evaluation parameters. In Chapter 6 a comparison of the various fuel saving measures is presented, including a table showing compatibility and main physical effects. A comprehensive list of the background documents is presented in Chapter 7.

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2.

Physical descriptions of the fuel efficiency measures

Fuel is saved when measures are taken to reduce ship resistance or improve the efficiency of machinery and propulsion. This section aims at providing a background for understanding the physical effects of various fuel saving measures. This is of special interest when e.g. discussing the combined effect or compatibility of various devices. In general, if two devices are designed to reduce the same type of loss, the combined effect will result in much lower savings than the sum of the predicted savings from each working separately. If the devices are not designed to work together, the combined effect may be a lower saving than using only the better or even the worse of the two. This section will briefly list and describe •

Resistance components

•

Propeller characteristics

•

Components around working propeller

An understanding of the physical mechanisms involved makes it easier to perform a proper assessment of the potential fuel savings. A basis in sound hydrodynamic theory gives the opportunity to give an upper bound to savings related to reduction of energy losses.

2.1

Resistance components

The resistance of a vessel is the force required to tow the vessel through water. The resistance of a bulk carrier in calm water can approximately be divided in the following components: •

75-90% viscous resistance

•

5-10% wave resistance

•

5-10% resistance due to roughness

•

Up to 5% air resistance

In addition to the above mentioned components a vessel trading in waves and/or wind experiences increased resistance. This guide will not treat means to reduce the added resistance or thrust loss in waves. The viscous resistance is governed by the wetted surface area and the form factor. It increases approximately linearly with the wetted surface area. The form factor accounts for the difference between the viscous resistance of a vessel and a flat plate with an equal wetted surface area. Usually, a full vessel (high block coefficient) has higher form factor than a slim vessel. The residual resistance is mostly due to wave making and it is dependent on the Froude number and on the vessel shape. The Froude number is the vessel forward speed divided by the square root of the ship length times the acceleration of gravity. Most large bulk carriers are operated at low speeds compared to the vessel length. This means that the

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Froude numbers are small and the wave making resistance is small compared to the viscous resistance. The resistance due to roughness accounts for the fact that a hull surface is not hydrodynamically smooth, but has a certain roughness. In the typical numbers presented above, the resistance due to roughness is only due to the surface roughness, and not additional roughness from marine growth. A fouled hull may cause a large increase in resistance, and maintaining a clean and smooth hull is imperative in order to save fuel. The air resistance is governed by the projected transversal area of the deck and the hull above the waterline and the relative drag coefficients. On bulk carriers the air resistance is typically low. However, the air resistance may be more significant if e.g. containers are carried on deck. MAN provides an excellent introduction to resistance, propulsion and ship powering. This is a recommended further read, see /21/.

2.2

Propeller characteristics

A propeller consists of a number of foil shaped blades that provide thrust as they rotate. Typical parameters a propeller designer has to consider are: •

Propeller type / configuration

•

Propeller diameter (propeller clearance, full immersion at ballast draft)

•

Propeller rotational speed / pitch

•

Blade area

•

Blade number

•

Profile shape

•

Geometrical details (camber, skew, rake, thickness, etc)

•

Cavitation performance in a wake field

•

Pressure pulses on the hull and noise radiated from the propeller

In an early project stage, only the 6 first issues are normally evaluated. Propeller type and configuration are often decided from operational aspects. For conventional cargo ships, a fixed pitch single screw, shaft line propeller without duct (nozzle) is most common. However, depending on the operational profile it will in some cases be beneficial to select a controllable pitch propeller, thruster propulsion, multi screw or ducted propellers. Even non-traditional propulsion devices like the Voith-Schneider propeller may be chosen. In order to maximize propeller open water efficiency, the basic principle is to give a large mass of water a small, axial acceleration. If there were no practical constraints, this would in general be obtained by having an as large propeller as possible rotating as slow as possible. The rotational speed is measured in number of rotations per minute, rpm. Open water propeller losses may be divided into frictional (viscous) losses and rotational losses (including vortex generation), where blade area and number mainly influence frictional losses. For a given diameter, the optimum combination of pitch and rpm is

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balanced by high rotational losses for high angles of attack (high pitch) and high frictional losses (high rpm). High pitch gives low rpm and vice versa. In general a low propeller to hull clearance is favourable on overall efficiency because it allows for a large diameter and also high hull efficiency due to recovery of energy losses in the ship wake. However, low clearances may be challenging with respect to propeller radiated noise and ship vibrations, and related requirements related to these issues set a practical lower limit for propeller to hull clearance.

2.3

Components around working propeller

The efficiency of a propeller behind a hull is mainly affected by the following parameters: •

Thrust deduction

•

Wake fraction

•

Open water efficiency

When a propeller is operating behind a hull, the flow field around the hull is changed. This increases the “hull resistance” and means that the generated thrust from the propeller has to be larger than the resistance measured without the propeller present. This increase in resistance is denoted thrust deduction. The wake fraction is a reduction in the inflow velocity seen by the propeller compared to the forward speed of the ship. This is caused by the presence of the hull and appendixes such as rudders, open shafts and brackets. The reduction in inflow velocity increases the efficiency of the propeller. The open water efficiency of the propeller is governed by the propeller design.

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Figure 1 Overview of nomenclature used in ship resistance and propulsion. From MAN B&W “Basic Principles of Ship Propulsion” /21/.

Most energy saving devices works by changing the flow before or after the propeller. Some devices aim at improving the propeller working conditions, while others seek to regain parts of one or more of the energy loss types caused by the basic principle of propulsion by a propeller. Typically they aim at affecting either one or more of the following: •

Axial wake

•

Tangential wake

•

Rotational losses

•

Vortices

•

Tip vortex

•

Hub vortex

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Figure 2 Typical sources of energy loss for a working propeller. From Mewis and Hollenbach /4/

One of the most difficult aspects when addressing energy efficiency measures is that most measures usually affect more than one parameter. E.g. making the aft body fuller may increase the form factor and the thrust deduction, and decrease the open water efficiency, all of which are negative effects. On the other hand, it may increase the wake fraction, which is a favourable effect. Hence, the net effect is difficult to assess without an analysis of the whole vessel. To complicate matters further, changes in propeller operating conditions may also affect the efficiency of the main engine. For all energy efficiency devices the aim will be to increase the total efficiency of the propulsion. This is also what the reported improvement values will relate to. Further information may be found in e.g. /21/.

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3.

General description of evaluation parameters

Each fuel saving measure will be evaluated based on the parameters discussed in the following sections. This is done in order to give a comprehensive overview of all the relevant aspects.

3.1.1

Description, including compatibility

It is helpful to understand how each fuel saving measure works. This is necessary in order to understand compatibility between different measures, and may help in a comparison between solutions working by similar principles.

3.1.2

Classification requirements

Different fuel saving measures could be subject to special requirements from the classification society. This will be evaluated for each separate measure. In general it is found that the need for Class involvement is limited.

3.1.3

Complexity of manufacturing

This section is relevant for energy saving devices and includes general comments regarding manufacturing. It is important that the device can be installed at a known cost without causing unplanned delays in the delivery of the vessel.

3.1.4

Range of expected fuel savings

The fuel savings will in general vary significantly for a given fuel saving device depending on the level of optimization of the studied design. In addition, some devices work well for certain ship types, sizes and speeds, but not for others. This document aims at providing an objective view of potential savings, and to the extent possible use high quality validation data obtained from relevant ship types.

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Figure 3 Possible power reduction including the Mewis Duct. From /1/.

The thrust loading coefficient is defined as: T CTh = 1 ρV 2 D 2 π 2 A 4, Where T is the propeller thrust, ρ is the fluid density, VA is the velocity of the propeller approaching the propeller and D is the propeller diameter. In the following discussion of the different fuel saving measures, most documentation of fuel savings for bulk carriers are scarce. Therefore also tanker specific results are presented especially since tankers and bulk carriers traditionally have a similar hull form.

3.1.5

Expected maintenance needs of device in operation

In order to do a proper return of investment analysis, the running costs need to be assessed as well as investment costs. Examples of maintenance needs could be cleaning or coating for hull and propeller appendages or changes in maintenance costs relative to a base-line for more energy efficient machinery.

3.1.6

Indication of price range

The price is typically based on information from suppliers, from manufacturer experience or from other published material.

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4.

Design and verification of fuel saving measures

The ship owner would like an accurate estimate of the fuel savings before deciding to purchase. After installation, it is valuable to know the actual savings. The effect of each measure varies depending on ship characteristics like size, hull lines, speed, propeller and rudder configuration. The reduction in power usage reported by suppliers may well be validated for certain designs, but some of the fuel saving devices should be optimized for each new vessel. Optimization requires a means to estimate savings. Validation also becomes important when different devices are combined, as compatibility issues may reduce the overall effectiveness. The Mewis duct for instance needs extensive analysis to fit the particular vessel and propeller, whereas a propeller rudder transition bulb is a more off-the-shelf product. Other fuel saving measures may be somewhere in between. A propeller nozzle with off the shelf design may give good performance, but can be improved by custom design resulting in a non axis symmetrical nozzle. Verification of fuel saving measures is challenging. The first and most fundamental question is “compared to what?”. Running tests simply with and without the device may give artificially high gains. It is reasonable to believe that if a vessel and propeller optimized for use of e.g. a pre swirl stator is tested without the pre swirl stator, the performance is worse than of a vessel and propeller optimized without considering the pre swirl stator. The performance of a fuel saving measure may be validated by full-scale measurements, model tests or numerical analyses. MARIN presents a framework for decision making relative to energy saving devices in Fathom’s report “Ship efficiency: The Guide” /27/. Here the research institute explains how CFD and model tests can be used in combination to achieve better validation of savings and partly address the shortcomings of both approaches.

4.1

Full scale measurements

Fuel savings measured by full-scale trials might appear to provide the best validation of a device’s performance. However, full-scale measurements are subject to limited measurement accuracy, poor control of the environment, and the effect of unexpected or unknown changes to the vessel between tests. When conducting measurements, it is common to make use of the onboard sensor system. However, the quality of such a system may vary significantly. If the sensor is not intended to provide high precision measurements, the accuracy may be insufficient. Since fuel saving measures often produce small gains, this uncertainty may be enough to disrupt the identification of any fuel saving. When predicting the performance based on a sea trial, correcting for environmental effects like wind, waves and current is a challenging task. How these corrections are conducted may have a significant effect, and will probably represent a major source of uncertainty. If a vessel is to be tested with and without a fuel saving device, it is often most practical to attach the device at docking. However, docking a vessel will usually imply a lot of other Page 18 of 84


changes to the vessel like e.g. cleaning of the hull, cleaning of the engine and painting the hull. These changes may be impossible to properly account for when trying to identify the effect of a fuel saving measure. When a fuel saving measure is first implemented on a sister vessel, the sea-trials should be a good basis for validation. However, differences between sister vessels may cloud the picture. High quality validation data is obtained from full-scale measurements by good planning and execution combined with careful post-processing and analysis.

4.2

Model tests

The International Towing Tank Conference (ITTC) 1999 report on unconventional propulsion /7/ addresses the issue of using model tests to assess the performance of various fuel saving devices. Towing tank organisations typically use extrapolation methods based on modifications of the ITTC 1978 approach. Some have developed a new methodology for each particular type of unconventional propulsor. The report explains that extreme cases, such as integrated ducted propulsors, cannot be adequately studied using the ITTC 1978 methodology, while for example pre- and post-swirl vanes, ducts and propeller pods have been dealt with by appropriate modifications. The standard correlation procedure fails to scale and predict the energy saving due to laminar flow on some devices at normal towing speeds. For some devices, reliable full-scale estimates of savings depend strongly on achieving the Froude and Reynolds number similarity. Partial ducts are reported to result in energy savings in full-scale trials, but the ITTC report concludes that this probably cannot be proven by model tank towing tests at Froude speed. Even cavitation tunnel tests at higher speeds may show uncertain trends. New testing procedures and the application of large high-Reynolds number water tunnels promise to improve fuel saving estimates. Another ITTC document /17/ discusses expected accuracy when conducting various types of model tests to study different fuel saving measures.

4.3

Computational fluid dynamics (CFD)

Similar to model tests, CFD simulations allow for accurate control of the measurements and the environment. Since CFD simulations can be conducted at full scale, the scaling problem of the model tests is avoided. However, when conducting CFD simulations it is important to have a firm understanding of the physics to be investigated. This is necessary in order to include the appropriate numerical models in the simulations. When addressing new topics, model tests should be conducted and simulations performed in either model or full scale to confirm the physical models. A mesh convergence study and a sensitivity study may also be necessary. ITTC has recommendations on how to perform such studies /17/. CFD is currently used by ship designers, research institutes, yards and classification societies to study a range of problems. The methods span from potential flow and calm water wave-making to unsteady turbulent free-surface flow around ships by Reynolds Averaged Navier Stokes (RANS) models. CFD may be extremely sensitive to the numerical models that are used for solving the physical problems. The results may also be strongly dependent on mesh quality. Problems Page 19 of 84


with mesh quality are somewhat easier to detect than errors in using the proper numerical models. In general, a simulation with a bad mesh will diverge (or never converge). On the other hand, the differences in using, say, different turbulence models may be much more subtle. A bad choice of turbulence model does not necessarily cause divergence, only inaccurate results. Experience has shown that even small changes in the setup may lead to divergence for simulation of the complex flow in the aft part of a high block vessel. It is rather difficult to issue a set of rules that help preventing this kind of errors. When it comes to meshing, in general commercial code generators have some quality criteria. If the mesh generator comes with the solver package, then it is expected that respecting the quality criteria for that particular solver yields an appropriate mesh. Convergence of the mesh is also an important issue. Again, it is difficult to issue a set of general rules. The most critical issue is the wall distance when turbulence models are used. The first layer of points where velocities are calculated should follow a logarithmic profile for the velocity profile calculated in the turbulent boundary layer, for which the wall functions are valid. If transition models are used, then the wall distance should be much smaller. This criterion is necessary but not sufficient. Numerical simulations may be cheaper and faster than model tests during the optimization process of the hull or energy saving device. This is due to high model manufacturing costs. If a fitting model exists or a large number of runs is required, model tests may well be cost efficient. However, the scaling issues inherent in model tests could mean that some CFD runs should be performed at full-scale to validate real savings at high Reynolds numbers. The main cost of numerical simulations is the required man hours spent setting up and executing the simulations. The license and hardware cost may also be significant. A rough estimate of the license and hardware cost is USD 500 per day.

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5.

Detailed evaluation of fuel saving measures

This chapter goes into detail on series of fuel saving measures. The list is not complete, and there are many other good candidates for e.g. fuel saving devices. This selection consists of popular measures intended to be representative.

5.1 5.1.1

Hull shape Physical description

It is believed that in future, flexibility with respect to both loading conditions and speeds will have a more significant impact on the ship design. In this respect it will be important to make a vessel that performs well over a wide range of drafts and speeds, and probably it will be less important to be able to achieve a high design speed at design draft. The hull shape determines the resistance of the vessel. In addition it also influences the flow conditions of the propeller. Therefore the hull to some extent has to be optimized together with the propeller. A generic optimal combination of the main hull dimensions is not achievable, since there are many constraints like, for example, a maximum draft due to port restrictions. Other parameters, like the vessel length, are driven by economical reasons such as the building cost and the fees. The hull shape is mostly depending on the Froude number at which the vessel operates. Bulk carriers are typically designed for a speed range between 12 and 16 knots, implying a low Froude number (usually between 0.12 and 0.22). The viscous resistance is therefore the dominating component of the hull resistance. This means that in the ship design the focus is in minimizing the viscous resistance more than the residual resistance. This typically results in vessels with high block coefficient with the draft set to the maximum allowable in the ports of call of the vessel. Smaller bulk carriers usually operate at higher Froude numbers (higher residual resistance and lower viscous resistance), allowing for a smaller block coefficient. Optimizing the bow shape for vessels with low Froude numbers usually has little impact on the calm water resistance but may have a considerable impact on the added resistance in waves. The stern shape influences the resistance and also determines the inflow conditions of the propeller. It is nowadays possible to use potential flow solvers and even automatic optimizers to determine the main hull parameters and the fore body shape in a relatively short time frame. Multiple speeds and loading conditions can be tested and the advantages of a particular design can be weighted against its disadvantages, for several operating profiles. In the near future numerical analyses should provide a practical tool in estimation of added resistance in waves. This will enable both design of an optimal fore body shape in waves and a more accurate dimensioning of the engine, refining the sea margin. DNV is currently developing such analysis tools. More advanced CFD softwares can be used for the combined design of the hull aft body shape and the propeller. Their relative influence can be estimated and an iterative optimizing process can be carried out. This is still an expensive and time consuming process. Page 21 of 84


Compatibility Optimizing the hull shape reduces the overall resistance, and is hence compatible with all other fuel saving measures. The propeller has to be optimized together with the hull shape.

5.1.2

Requirements from classification

There should not be any additional requirement for the classification beside the fact that different hull dimension implies different structural dimensioning. A forebody shape with reduced added resistance in waves may also perform better with regards to slamming loads. However, some wave piercing bows may give a larger number of slamming events, which implies that fatigue needs to be evaluated.

5.1.3


The selection of dimension ratios, bow shape and aft body optimization should be well considered and optimized based on a database, CFD simulations or even by model test. This is a time consuming task. Further comparisons should be carried out between different design options. The optimization on bow shape and aft body may be performed with the help of CFD analyses. The wave making resistance may be reduced based on potential flow software and the viscous resistance may be investigated and optimized based on a viscous code (RANS – Reynolds Averaged Navier Stokes). Self-propulsion tests may also be simulated using CFD. CAD softwares allow for parametric hull variation generation. Combined with CFD analyses, a large number of variations can be automatically generated and evaluated to optimize the solution in regards to a set of constraints (fuel consumption, deadweight, speed,…) using for example genetic algorithm optimization.

5.1.4

Range of expected fuel saving

Typically savings of up to 10% are estimated when comparing a highly optimized hull with a typical basis design. Table 1. Reported fuel savings for hull design.

Source

Ship type

Design draught Up to 7% container 8%

Wärtsilä Mærsk Fathom /27/ IMarEST /29/

5.1.5

Ballast draught

Comments

Important spread in operation profile, high potential for savings

Up to 10% 0-2%

Expected maintenance needs

There are no special maintenance needs related to a different hull shape.

Page 22 of 84


5.1.6


The cost of hull optimization is related to time consuming design work and analyses to assess the potential fuel savings. This cost should include CFD simulation computing time and possibly towing tank testing.

Page 23 of 84


5.2

Openings – Arrangement and design

Figure 4 Examples of some openings designs, courtesy of HSVA.

5.2.1

Physical description

Openings in the hull are needed for sea chests and bow/stern thrusters. The detailed configuration of these openings is important for resistance as well as noise and vibration. The efficiency of the thrusters is dependent on the shape of the tunnel. Use of scallops or grids could reduce the turbulent flow induced by the opening and associated losses. Worst case, the openings may lead to flow separation. Fairings may be an efficient means to improve the flow characteristics, but care should be taken not to adversely affect the thruster performance. Page 24 of 84


Compatibility Hull openings reduce locally the hull resistance. The openings located at the stern might influence the propeller inflow so that their interaction with other devices located at the stern should be carefully studied.

5.2.2


Special design of the openings will not influence the classification scope of work, as long as no new types of structures are added to the design, e.g thruster tunnels or sea chest.

5.2.3


The additional resistance created by such openings need to be minimized by careful design. The scallop at the aft end should prevent the outflow from the thruster to be slowed down. The direction of the bars covering the openings need to be considered relative to the local flow direction. Openings with scallop are slightly more complex for manufacturing.

5.2.4


Table 2. Reported fuel savings for openings – arrangement and design.

Source Ship type Design draught Ballast draught Comments Wärtsilä 1-5% 1-5% From /27/

5.2.5


Use of grids may imply a higher risk of marine growth or attachment of dirt or other foreign matter. Except for cleaning, no specific maintenance needs are identified.

5.2.6


There is no specific additional cost of a better design of openings, and addition of a grid is inexpensive.

Page 25 of 84


5.3

Mewis Duct

Figure 5 Installed Mewis Duct on Grieg I-class vessel. From /1/.

The Mewis Duct (MD) is a new energy saving device invented and designed by Friedrich Mewis for full-form slower ships. Financing, development and construction was done by Becker Marine Systems, and this company now promotes and sells the device. The Mewis duct has been installed, among others, on the Grieg I-class vessels, see /24/ and /25/.

5.3.1


The MD is a combination of a vertically offset mounted duct positioned right in front of the propeller and an integrated asymmetric fin arrangement. The duct diameter is smaller than the propeller diameter, and the fins chord length only covers parts of the ducts length. Since the fins are located within the duct they will not produce fin tip vortices. The Mewis duct combines the effects of a wake equalizing duct and pre-swirl fins within a single unit. This is expected to increase the total efficiency gain compared to the sum of the two separate effects. The Mewis duct aims at affecting two aspects. The duct improves the characteristics of the ship wake flow in addition to generate self-thrust. The fins aim at producing a pre swirl that improves the tangential inflow speed to the propeller. The pre swirl is claimed to reduce the rotational losses and also contribute to a reduction of energy loss due to generation of hub vorticity.

Page 26 of 84


Figure 6 CFD plots in plane after Mewis duct and before propeller. Courtesy of Becker Marine Systems. From /30/.

Optimization and verification for specific ship installation The MD should be optimized for a given ship. The designer explains that an MD with 5 fins has 53 free parameters that should be included in the optimization. Experience of the designer is the basic method, but this should be complemented by CFD (RANS) analyses to find e.g. appropriate fin profiles, estimate wake field, assess flow field ahead and behind the propeller, look at the flow and forces on duct and fins. It is important to study modelscale effects vs. full-scale effects.

Page 27 of 84


Verification of the results should be executed by means of sea-trials with adequate measuring equipment before and after installation of the Mewis duct. Typical setup should as a minimum be: •

Unchanged hull condition pre and post installation

•

Unchanged propeller condition pre and post installation

•

Calm sea state

•

Sea trial executed by multiple double runs

•

Accurate measurements of speed

•

Accurate measurements of RPM

•

Accurate measurements of shaft torque

As a substitute to full scale measurements one may use full scale CFD simulations. Compatibility Since the MD works in several ways, it is not compatible with other fuel saving devices acting to reduce the same losses: wake equalizing ducts and pre-swirl fins. The inventor reports that the Mewis Duct is suited for vessels with a high block, speed below 21 knots and a thrust loading coefficient above 1. This fits well with bulk carriers of all sizes.

5.3.2


The duct itself is not subject to approval, only the connection to hull structure is evaluated based on the reaction forces from the duct. For vessels with ice class the installation of such a duct needs special consideration. It should be noted that in the case where the propeller is arranged inside the duct (see next paragraph), the duct is subject to approval because of higher dynamic loading from the propeller.

5.3.3


The MD inventor claims that this device does not much influence the RPM of the propeller, and may thus be retrofitted without changes to the propeller. The Mewis Duct is a special duct with 4 or 5 stators inside. It’s a product of Becker Marine System. The duct and stators are double plated constructions forming a hydrodymamic streamlined section. According to normal procedure, BMS itself will cover following work scope: -

Design and supply of the MEWIS Duct system to the satisfaction of Class. Full Class certification of major BMS supplied MEWIS Duct components. Verification and class approved structure. Verification and class approved connection between MEWIS Duct and Ship structure. Class survey fees at BMS sub-contractors and suppliers. Design interface with Ship Designer.

Page 28 of 84


-

Extract of the results from the tank tests with MEWIS Duct in an European towing tank establishment. Supervision by BMS of 5 days for installation of each MEWIS Duct.

And for the shipyard, it’s their duty to weld the MEWIS Duct onto the hull body and consider relevant strengthening inside the main hull body which should be approved by classification society.

5.3.4


Error! Reference source not found. Table 3 shows an overview of reported ranges of fuel saving for the Mewis Duct. In summary, a 5% saving is a conservative estimate. Table 3. Reported fuel savings for Mewis duct.

Source

Ship type

Hollenbach /15/ Hollenbach /15/

45K Bulker 118K Bulker 47k Bulker

Mewis /1/ Svardal and Mewis /23/ HSVA /15/ ITTC /7/

12k Bulker

Design draught 6,0% 6,9%

Ballast draught 5,4%

6,0%

Comments Model test Model test Estimated saving

7.7%

VLCC

5% 4-9%

The inventor claims power savings in the order of 7-9% for bulk carriers. The IBMV from Rostock has performed numerical calculations, and model tests have been carried out at HSVA, SVA and SSPA to validate savings.

5.3.5


Becker Marine Systems claim that there will be no particular maintenance needs related to the Mewis duct. It is expected that one will perform normal maintenance such as cleaning and re-coating of the Mewis Duct during dry-docking. This is not expected to impose any significant complications or costs.

5.3.6


Table 4Error! Reference source not found. presents typical costs for a Mewis Duct from SDARI experience. Table 4 Mewis Duct costs

Ship type / size Panamax Capesize

Page 29 of 84

Design package 140 kUSD 140 kUSD

Price per unit 210 kUSD 290 kUSD


5.4

Propeller nozzle

A ducted propeller or propeller with nozzle consists of a nozzle and specially designed propeller. It is important that the clearance between the propeller and nozzle is as small as practically possible. The duct has an airfoil cross-section or profile. The efficiency gain is very dependent on the thrust load coefficient. For normal operation of bulk carriers, only a small increase in power efficiency is expected. An efficiency improving propeller nozzle changes the flow field in and around the propeller and divides the thrust force among itself and the propeller.

5.4.1


There are two main types of nozzles; the accelerating and the decelerating nozzle. The type of nozzle considered for efficiency improvements is the accelerating nozzle. The decelerating nozzle is used to improve cavitation and noise properties. The accelerating nozzle, as the name indicates, accelerates the flow through the propeller. At bollard pull conditions, this reduces the propeller thrust, but generates a significant thrust on the nozzle, such that the total thrust is larger than for the propeller alone. As the forward speed of the vessel increases, the drag of the duct increases and the net force from the duct is reduced. From a certain advance speed, the total thrust becomes smaller than for the propeller alone. According to /8/ from the 1970’s, a ducted propeller may be preferred with Bp values above 25. Bp = N P

Va 2.5 ,

Where N is shaft speed in RPM, P is power in HP and Va is advance speed in knots. Compatibility Since the non axis symmetrical nozzle changes the wake field of the propeller, the effect of combining it with a PSS device is somewhat uncertain. Axis symmetrical nozzles are expected to have a larger benefit from a PSS than non axis symmetrical nozzles.

5.4.2


Example of class general requirements can be found in DNV Rules for Ships Part 3, Chapter 3, Section 2.H. It should be noted that for large propeller nozzles, scantlings and arrangement is to be specially considered with respect to the exiting frequencies from the propeller. In order to prevent corrosion and erosion of the inner surface of the nozzle, application of a corrosion resistant material in the propeller zone is recommended.

5.4.3


Nozzles are airfoil shaped rings around the propeller. An advantage of the nozzle is that it increases the total thrust. From the design point of view, the nozzle profile is most important for efficiency. But at high ship speeds the nozzle generates drag instead of thrust. So the opportunity of using this device should be evaluated based on the operational profile of the vessel. Page 30 of 84


The nozzle is a double plated construction forming a hydrodynamic streamlined section. It may be manufactured by the yard itself or it may be provided by a particular manufacturer. The nozzle may be fixed on the hull or acts as a nozzle rudder, meaning that the direction of thrust can be changed to support the manoeuvring of the vessel.

5.4.4


According to /8/ from the 1970’s, the following fuel savings at loaded condition for a tanker can be expected: - Conventional stern and axis symmetrical ducted propeller, 2-6%. - Conventional stern and non axis symmetrical ducted propeller, 6-9%. - Ship with cigar-shaped stern and axis symmetrical ducted propeller, 5-8%. The expected fuel saving at ballast condition is 2-3% larger. Due to the similarity between tankers and bulk carriers, the same savings are expected also for bulk carriers. Wärtsilä claims that their new HR-nozzle is able to improve the propulsive efficiency with 10% compared to an open propeller when operating at speeds common for bulk ships.

Figure 7 Illustration of possible increase in propulsive efficiency by use of a propeller nozzle. From /16/.

Table 5. Reported fuel savings for propeller nozzle.

Source Ship type Design draught Ballast draught Comments ITTC /12/ 5-12% Mewis /1/ 0-7%

5.4.5


The propeller nozzle should be cleaned at regular intervals. The structure should be inspected as part of regular class surveys. Page 31 of 84


5.4.6


The cost of a propeller nozzle system varies significantly based on type , design and manufacturer. As an example a HR nozzle from Wärtsila has been quoted at approx.. € 150 000,-

Page 32 of 84


5.5

Pre duct

There are several pre duct devices available on the market, for example the Sumitomo Integrated Lammeren Duct SILD and the Schneekluth Duct (WED), shown in Figure 8.

Figure 8 Schneekluth WED, courtesy of Schneekluth

5.5.1


The Sumitomo Integrated Lammeren Duct (SILD) is a circular flow accelerating duct. Its diameter is about 70% of the propeller diameter and it is mounted non-centric in front of the propeller. The aim is to save fuel but also improve manoeuvrability and reduce hull vibrations. The Schneekluth wake equalizing duct (WED) is fitted to optimize the propulsion properties by improving the flow into the propeller. More than 1500 applications as retrofits and newbuilds are reported. A typical diameter is about 3m. Other important characteristics are the angle of inclination at the base and the opening angle of the semi-duct relative to the centre-line plane being different for port and starboard sides. The distance to the propeller plane and total depth of the WED are also important. The design includes two spoilers at both ends upstream of the lower edge of the duct to avoid flow separation at the outer surface of the duct in this area. The WED accelerates the flow and directs it towards the area of maximum non-uniformity in the propeller disk, i.e. 12 o’clock position. This renders a more homogeneous wake. The WED also produces thrust. Compatibility The Pre Ducts are accelerating the propeller inflow and equalizing the wake. They are in theory compatible with the down stream devices located after the propeller. However, a careful analysis needs to be carried out to when planning on integrate several devices acting on different aspects of the flow.

Page 33 of 84


5.5.2


Similarly to the Mewis Duct, the duct itself is not subject to approval, only the connection to hull structure is evaluated based on the reaction forces from the duct. For vessels with ice class the installation of such a duct needs special consideration.

5.5.3


Table 6. Reported fuel savings for Pre Duct.

Source

Ship type

Svardal and Mewis /24/ Fathom /27/ Fathom /27/

12k-46k Bulker

5.5.4

Design draught 2-3% 5% 5-6%

Ballast draught

Comments Pre ducts WED Simplified compensative nozzle


There will in general be no particular maintenance needs, but the duct will experience significant hydrodynamic loads, so that inspections should be carried to look for possible cracks at the intersection with the hull.

5.5.5


According to the manufacturer, a WED for a Handymax bulk with a propeller of 6.6m diameter costs approximately 90 000 Euro, with an 8 to 10 weeks delivery time, all included (consulting, design, calculation, approval).

Page 34 of 84


5.6

Pre-swirl stator

Figure 9 Pre-swirl stator. Courtesy of DSME.

5.6.1


The Pre-Swirl Stator (PSS) consists of a set of blades positioned right in front of the propeller. The PSS changes the inflow to the propeller and improves the propulsion efficiency. Daewoo Shipbuilding and Marine Engineering, DSME, holds a patent for a PSS device, while various other similar devices are offered by other makers and yards. The DSME patent includes three blades on port side (45, 90 and 135 deg with the vertical) and one blade on starboard side (90 deg with the vertical). It appears that the pitch of each blade is uniform as function of the radius. A further development of this may be to twist the blades to introduce a non uniform radial pitch distribution. However, this will significantly complicate manufacturing. The blades typically have different pitch angles. The idea behind the invention is to introduce a pre-swirl ahead of the propeller in order to reduce the rotational losses. The PSS is also reported to have a favourable effect on the wake. Since the wake field is different in model scale and full scale, there is some uncertainty in the estimated effect of the PSS from model tests. Compatibility The PSS is working with flow rotation and should not be used with other similar devices like Propeller boss cap fins or Contra rotating propellers. To associate the PSS with nozzles or ducts is not recommended either. The Mewis duct is itself combining a PSS with a duct..

Page 35 of 84


5.6.2


The stator itself is not subject to approval, but the connection to hull structure needs to be evaluated based on estimated forces on the foils. For vessels with ice class installation of appendages like the pre-swirl stators needs special consideration.

5.6.3


The Pre-swirl stator is a fin system and resembling small rudders radially arranged before the propeller. A typical installation includes 3-6 stators. It is a symmetrical distribution when a design with 6 stators is employed, otherwise an asymmetrical distribution will be used. From the design point of view, the number and distribution of the stators are quite important. The profile, pitch and chord length of each stator should also be optimized to improve efficiency gain. The strength of each component should be calculated by FEM method according to hydrodynamic loading. The yard may manufacture and install PSS by themselves as per design drawings.

5.6.4


HSVA reports up to 5% power saving /9/. Savings in the order of 4-6% is expected based on model test results. Table 7. Reported fuel savings for pre swirl stator.

Source HSVA /9/ HSVA /14/ HSVA /14/ ITTC /12/ Ship Propulsion Solutions /13/ ITTC/7/ Mewis /1/ Svardal and Mewis /24/

5.6.5

Ship type Container VLCC

Design draught Ballast draught Up to 5% Up to 6%, Typically 2% typically 3% 5% 5% 3-8% 4-6% 3-9%

12-46k Bulker

3-5% 2-3%

Comments

Hydrodynamic fins Pre swirl fin systems


There are no expected needs of maintenance except for cleaning. The classification society will look for cracks in the intersection between the stators and the hull during normal docking survey.

Page 36 of 84


5.6.6


Table 8Error! Reference source not found. presents approximate costs for a pre-swirl stator installation. The design package includes optimization with support of CFD simulations and towing tank tests.

Page 37 of 84


Table 8 Pre-swirl stator costs

Ship type / size 30 kdwt 205 kdwt

Page 38 of 84




5.7 5.7.1

Propeller design Physical description

The following main parameters for propeller design are influencing the open water efficiency: •

Diameter

•

Rotational speed / Pitch ratio

•

Number of blades

•

Blade area ratio

To a large extent, these main parameters may be optimized and selected on the basis of experimental data from propeller series, such as the Wageningen B-series. Additionally, operational aspects such as ship speed, resistance (or required power) and propulsive coefficients must be known or at least estimated. Detailed design parameters will also influence the efficiency, to a smaller extent: •

Camber

•

Skew

•

Rake

•

Chord length

•

Thickness

•

Profile

•

Tip fin

Propeller diameter should in general be as large as possible. However the presence of the hull above the propeller normally limits the maximum possible propeller diameter. A certain clearance between the propeller tip and the hull plating should be provided, depending on the propeller operational conditions and requirements to noise and vibration. Increasing the distance between the propeller and the hull in general leads to less transfer of propeller induced noise and vibrations into the hull / ship. On the other hand, a larger propeller size (but smaller clearance) reduces the specific propeller load, which may reduce radiated noise and pressure pulses. In general, propeller tip clearances are typically in the range of 15 to 25% of propeller diameter. In order to take advantage of a large propeller diameter, it is necessary to run at a sufficiently low RPM. In many cases, the available RPM range is limited by the engine selection and /or possibilities for reducing the RPM with a gear system. The propeller pitch and RPM are selected in combination – a relatively high RPM leads to a low pitch and vice versa. Number of blades should in general be chosen as low as possible from an efficiency point of view. 4 blades is normally a starting point (except for very small propellers, which may be 3 or even 2 bladed), but a higher No. of blades may be necessary to avoid excitation of Page 39 of 84


harmful resonances, in particular torsional vibrations in the shafting system. As a general trend, dynamic shaft forces and moments can be significantly reduced by increasing the No. of blades. The first and second order blade excitation frequencies can be predicted with good accuracy and are usually used as input to the propeller design. The excitation forces on the hull just above the propeller are also reduced by increasing the No. of blades, but to a lower extent. The excitation frequency will increase. This is also depending on the shape of the wake field. Finally, it should be noted that as the No. of blades increases, the optimum propeller diameter is in general reduced, due to the conservation of momentum. Blade area ratio should also be selected as low as possible in order to obtain a high efficiency. However, a certain minimum area is required in order to avoid heavy cavitation, which may generate large dynamic forces in the aft ship (and hence vibrations) as well as cavitation erosion. On the project stage, it is sufficient to select the blade area ratio from empirical methods, such as the criteria given by Burril or Keller. These criteria differ with the No. of blades, so that both the No. of blades and the blade area ratio should be selected through an iterative process. The detailed design parameters will normally have less influence on the propeller efficiency than the main parameters. However, by an optimum combination of the design details, it may be possible to influence significantly the cavitation performance. A successful design may hence allow more “radical” values in the selection of the main parameters, i.e. lower tip clearance (large diameter), lower blade area ratio, etc – which again may lead to increased efficiency. Special design features, such as Kappel tip fin propeller or Wartsila tip rake propeller may increase efficiency. Makers claim the possible gains to be in the order of 3-5%. High skew should not lead to significantly higher efficiency directly, and the opposite effect has to some extent been claimed. However, high skew may allow for larger diameter and/or lower blade area ratio, which may improve efficiency. Compatibility Any modification to the flow around the hull will have an effect on the propeller efficiency. Not only by modifying the hull shape or adding a fuel saving device before the propeller, but also by changing the loading, the trim and the speed. It is critical to maintain the propeller efficiency at its highest.

5.7.2


The classification societies have requirements related to scantlings of propellers, see for example DNV Rules Part 4, Chapter 5, Sec 1. This will determine minimum acceptable values for blade chord length and thickness, as well as propeller hub diameter and length.

5.7.3


From the design point of view, special propellers such as the NHV (No Hub Vortex) propeller or tip-rake propeller may eliminate or at least reduce hub and tip vortices. A NHV propeller controls the flow water by special pitch distribution. Tip-rake propellers have blades curved towards the tips. Well-manufactured propeller with more accurate offsets and smoother surface will benefit the efficiency. Page 40 of 84


5.7.4


Table 9. Reported fuel savings for propeller design.

Source

Ship type

ITTC /12/ Stierman /11/ Stierman /11/ Stierman /11/

5.7.5

Bulk carrier 35k Bulk carrier 270k Tanker

Design draught

Ballast draught 5-18% 10% 0%

14%

24%

15%

15%

Comments Low RPM propeller Low RPM propeller Tip vortex free propeller, winglets at propeller tip with nozzle in front. Redesigned later without nozzle.


No specific maintenance is needed.

5.7.6


A special or well-manufactured propeller will be about 5% more expensive than a standard product.

Page 41 of 84


5.8

Contra rotating propeller

Figure 10. Contra rotating propeller from Mitsubishi Heavy Industries, LTD

5.8.1


The contra-rotating propeller consists of two propellers where one is positioned downstream of the other, partly or totally overlapping and rotating in the opposite direction. The two propellers can be mounted on two thruster units, on an internal and external shaft, or the intermediate solution: one conventional shaft plus one contra rotating thruster. A special case is the Grim’s vane wheel, which is a propeller shaped installation free to rotate behind the normal propeller. Compatibility The contra-rotating propeller should not be combined with any other measure affecting the propeller inflow or near flow: ducts and nozzles, boss cap fins, pre swirl stators, rudder transition bulb.

5.8.2


There are various aspects of the complex contra-rotating propeller installation that may require special consideration by classification. A general discussion is hard due to the many different available solutions. Typically the packages offered by various suppliers have some level of general approval and the main focus is on the integration with the hull and machinery.

5.8.3


Many different contra rotating propeller systems have been developed. Normally they are quite complicated compared with the configuration with normal diesel engine and a single propeller. In the following a CRP system from IHIMU is compared with a normal configuration. This system is a diesel-electric CRP system, which consists of two concentric shafts. Thus a special gear box and shaft system is needed. Special considerations on shaft alignment, arrangement etc. is necessary. A good design and careful manufacturing are needed for this complicated system.

Page 42 of 84


Figure 11 IHMU CRP system on diesel-electric driven vessels

5.8.4


Table 10. Reported fuel savings for coaxial contra rotating propeller.

Source Ghassemi /18/ Ghassemi /18/ ITTC /12/ Min /20/ Stierman /11/ Stierman /11/ Mewis /1/

Page 43 of 84

Ship type VLCC Bulk carrier

Tanker All vessel types

Design draught

Ballast draught 7% 2% 7-20% 8% 5% 5-12%

Comments

7-14%


5.8.5


The expected maintenance need depends on the system selected. As a CRP system includes changes to the machinery system, and the overall complexity of the installation is high, a corresponding increase in maintenance is to be expected.

5.8.6


The system is in general complicated, and it is not so easy to get and idea of how much more expensive it is than a typical standard propulsion and machinery system onboard a bulk carrier. According to IHI’s experience a return of investment within 3 years may be reasonable.

Page 44 of 84


5.9

Propeller Boss Cap Fins and Propeller Cap Turbines

Figure 12 Propeller boss cap fins. From /1/ and /2/.

In recent advertisements MOTech, Mitsui O.S.K Techno-Trade, Ltd., reports more than 1700 installations with average savings of 5% for their patented Propeller Boss Cap Fin, PBCF.

5.9.1


A propeller generates vortices from its hub. This means loss of kinetic energy and a reduction of propulsive efficiency. The shed vorticity may increase the risk of cavitation. The magnitude of the vortices will depend on the blade radial loading distribution, and on the size and design of the hub. Properly designed hub caps can reduce the hub vortex generation, and improving the overall propeller efficiency by also reducing other losses. The propeller boss cap fin (PBCF) and propeller cap turbine (PCT) both consists of small fins attached to the propeller hub. The number of fins is equal to the number of blades on the propeller in the PBCF patent. The energy from the rotating fluid coming off the propeller hub is recovered by the foils. Figure 12 shows two examples of PBCFs. The concept has been developed and published by a group of Japanese inventors. Most research and development work on PBCF have been reported by the technical departments of the Mitsui O.S.K Lines, Ltd., West Japan Fluid Engineering Laboratory Co. Ltd and the Mikado Propeller Co Ltd. who are the joint patent holders of the device /6/. The propeller cap turbine is proposed as an improvement over the propeller boss cap fins. Curved instead of flat bades can be used /3/. There are no apparent limitations to the type of ship / propeller on which the PBCF or PCT can be installed, even CP propellers have been fitted with PCT. RPM is only slightly changed, even if the propeller torque is reduced by 3-5% /3/. Open-water propeller tests may be conducted to design the PCT, preferably in a cavitation tunnel. However, the presence of a rudder may significantly reduce the strength of the hub Page 45 of 84


vortex and hence the estimated gain in propeller efficiency. Published results show that the rudder may reduce the gain due to PBCF by 10-20% /6/. Compatibility The PBCF or PCT should be compatible with devices that are used to reduce rotational losses (pre-swirl stators) and improve the propeller wake (nozzles and ducts).

5.9.2


The PBCF and PCT do not contain moving parts. There are no specific requirements from classification for the PBCF.

5.9.3


PBCF is a device installed instead of normal hub cap. It is a combination of a normal cap and a number of small foils matching the propeller blade number.. The manufacturer will provide the PBCF. The only thing to be specially considered by the yard is the strength of connecting bolts and the clearance between the PBCF and rudder.

5.9.4


There are different numbers surfacing for expected fuel savings. Mewis /1/ and Ship Propulsion Solutions /3/ refer to designer claims of power saving in the range from 2-4%. Other references state that the inventors of the device state a propeller efficiency increase from 3-7% or more commonly from 3-5%. HSVA reports up to 3% /9/. Independent assessments of Mewis and Hollenbach /4/ indicate up to 3% gain in efficiency, while Mewis in /1/ reports from 2 to 4% depending on the thrust loading coefficient. Gearhart and McBride /5/ indicate 5%. The gain in power (measurements at full scale) is 4%, according to Ouchi /6/. The 22nd ITTC specialist committee on unconventional propulsors present a detailed description on the validation done of PBCF efficiency. Alternative devices are also presented. A typical 5% increase in efficiency is reported. Table 11. Reported fuel savings for propeller boss cap fins and propeller cap turbines.

Source Ship type HSVA /9/ Mewis and Hollenbach /4/ Mewis /1/ Gearhart and McBride /5/ ITTC /7/ Ship Propulsion Solutions /13/ Svardal and Mewis /23/

5.9.5

Design draught Ballast draught Comments 3% 3% 2-4% 5% 5% 2-4% 3-4%


No specific maintenance is expected.

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5.9.6


An economic study performed by Renilson Marine on the return over investment for mounting the PBCF shows break-even periods between 2.2 months for containerships and 13.7 months for general cargo ships. The assessment considered a $350/ton price for fuel oil and a cost of the PBCF (all included) between $185,000 for the containership and $40,000 for a general cargo ship. The cost of a well designed hub cap should not be much greater than one that has not been so well designed. Table 12 gives estimated costs of the Propeller Boss Cap Fin. The design package includes design and optimization with support of CFD simulations and towing tank tests. Assumed delivery is “CIF” east Asia area. The cost estimates are rough. Table 12 Propeller Boss Cap Fin costs

Ship type / size 30 kdwt 205 kdwt



Renilson Marine Consulting Pty Ltd reports the following costs for Mitui’s PCBF, see /2/:

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5.10 Propeller rudder transition bulb

Figure 13 Propeller rudder transition bulb. Courtesy of DSME.

Figure 14 Costa bulb. From /24/.

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Figure 15 PROMAS integrated propulsion manoeuvring system. Courtesy of Rolls-Royce Marine.

5.10.1 Physical description The “original” propeller rudder transition bulb is the “Costa” bulb. The “Costa” bulb is simply a bulb attached to the rudder directly behind the propeller boss. The idea behind the invention is to reduce the hub vortex losses. The Taylor wake fraction is increased due to a potential effect on the bulb, the contraction of the slipstream is reduced and the wake field becomes more homogeneous. A propeller rudder transition bulb is often a central part of any high efficiency rudder. Therefore, the energy savings due to the bulb alone may be difficult to quantify. Examples are ERGOPACK from Wärtsilä and PROMAS from Rolls-Royce Marine. For both systems, the rudder and propeller are integrated and the propeller design is adapted to the rudder. Compatibility The rudder transition bulb is located just behind the propeller, so it is not compatible with Propeller boss cap fin and Contra rotating propeller. It might be compatible with other devices such as ducts and pre swirl stators. It is compatible with an optimized rudder profile.

5.10.2 Requirements from classification The integrated systems need to be checked and approved by classification. The transition rudder is considered as a part of the rudder structure and is approved in accordance to the rules for Rudders, see for example DNV Rules Part 3, Chapter 3, Section 2. The interface between the propeller / rudder system and hull and shaft must be specially investigated with respect to strength and fatigue.

5.10.3 Complexity of manufacturing From the design point of view, the rudder bulb should be optimized and the final result should be rechecked together with the propeller design. Manufacturing of a rudder bulb is quite convenient for yards. One disadvantage caused by the rudder bulb is that the bulb must be cut off to dismantle the propeller without dismounting the rudder blade. Page 49 of 84


5.10.4 Range of expected fuel saving Considering the propeller rudder transition bulb in connection with high efficiency rudders, some suppliers claim savings between 2-9% /10/. Expected savings are in the order of 2-4 % according to ITTC /7/. HSVA /9/ reports savings in up to 6%. These numbers are not specific for bulk carriers. However high efficiency gains for these devices are usually expected for heavily loaded propellers (bulk carriers usually have heavily loaded propellers). Table 13. Reported fuel savings for propeller rudder transition bulb.

Source

Ship type

Design draught

Ballast draught Up to 6%

HSVA /9/ HSVA /9/ Ship Propulsion Solutions /13/ ITTC /7/ Mewis /1/ Fathom /27/ Fathom Description/27/

Up to 3% 2-4% 2-4% 0-3% 6-9% (supplier) 2-9% (supplier)

Comments Efficiency rudders Costa bulb Costa bulb Costa bulb Costa bulb PROMAS ENERGOPAC

5.10.5 Expected maintenance needs No special maintenance is foreseen.

5.10.6 Indication of price range There is no significant cost for the yard to make a propeller rudder transition bulb. The GSF Bulk Carrier concept reports a price of 160 kUSD for a twisted spade rudder with Costa bulb /23/. The PROMAS integrated propeller and rudder is quoted for approximately 1 Million USD for a Handymax Bulk carrier.

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5.11 Rudder profile The rudder is a foil that is used to generate a sideway force that is needed to manoeuvre the vessel.

5.11.1 Physical description The rudder design is a compromise between propulsive efficiency, cavitation performance and manoeuvrability with a high stall angle.

Figure 16 Different standard rudder profiles. From /26/.

In normal operation thinner rudder profiles have less drag, but are more likely to develop separated flow and cavitation. During manoeuvring, thinner profiles may stall easier, leading to reduced manoeuvring performance. Twisted rudder design will improve the total propulsive efficiency, as the twist should adapt the rudder to the rotation of the propeller slipstream and reduce the local angle of attack on the leading edge of the rudder. Becker Marine Systems holds a patent for a refined rudder profile called the twisted leading edge rudder, which aims at aligning the rudder with the propeller flow. For a right turning propeller, the leading edge is moved slightly to port from the centre line above the boss and slightly to starboard below the boss. The twisted leading edge reduces the risk against slow separation and cavitation, hence allowing a thinner rudder profile. Roll’s Royce is also proposing a twisted rudder design. Compatibility An optimized rudder profile is in theory compatible with all other flow modifying devices. The rudder twist should be adapted to the rotation of the propeller slip stream.

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5.11.2 Requirements from classification The selection of rudder profile and the application of propulsive efficient designs will have an impact on the design loads acting on the rudder system. E.g. high lift rudders will typically experience increased rudder torque. While class may have incorporated handling procedures in the Rules and instructions for concepts that are frequently applied, other novel designs may need special considerations in the class verification process. For special rudder designs, direct calculations may be required in the documentation of the rudder system.

5.11.3 Complexity of manufacturing Normally the rudder profile and arrangement will not significantly affect the complexity of manufacture. But for some thinner profiles, strength should be checked carefully and some special local strengthening may be needed. From the design point of view, a smaller and thinner rudder will benefit the propulsion efficiency. Rudders with high lift profiles can lead to substantial power savings. Rudders with a twisted leading edge can also lead to power gain compared with non twisted rudders. The power consumption can be reduced by shifting the propeller and rudder further aft.

5.11.4 Range of expected fuel saving Expected fuel savings are in the order of 1-2%. HSVA reports fuel saving up to 2% /9/. Table 14. Reported fuel savings for rudder profile.

Source

Ship type

HSVA /9/ ITTC /7/

Design draught

Ballast draught Up to 2% 2-4%

Comments Twisted rudder Reaction rudder, (asym. Rudder)

5.11.5 Expected maintenance needs There are no specific maintenance needs.

5.11.6 Indication of price range Normally no significant additional cost is expected for a different profile. However, this is not the case if some patent profile is used or the rudder is bought as a final item by a supplier.

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5.12 Main engine 5.12.1 Physical description The selection of the ship’s main engine is a complex problem, only the features that may offer fuel savings are highlighted here. Bulk carriers are generally fitted with two-stroke diesel engines installed as main engine with a SMCR ranging from 6 000 kW for a Handymax size vessel to 35 000kW for a VLBC. The most common engines for these sizes of ships are mechanically controlled engines. Electronically controlled engines are becoming more common for newer vessels. A diesel engine converts the fuel chemical energy into mechanical energy for the shaft. Only a small fraction of the fuel chemical energy can be converted this way. This fraction is called the efficiency of the engine, and amounts to approx 45 % for bulk carriers engines. The 55% of the chemical energy left is lost in the form of heat – roughly 45 % in hot exhaust gases and 10 % to the cooling water. This means that there is a lot of heat available onboard; the problem is usually that the need for heat is limited. Only a small fraction of this thermal energy is used, for example by boilers using the heat of the exhaust gases to warm up the accommodation area. In principle, it is possible to convert a part – but only a limited part – of this thermal energy to mechanical energy. One possibility is the Waste Heat Recovery System discussed below (paragraph 5.14), namely to run a steam turbine on the exhaust boiler steam. Another possibility is to use an “ORC” – Organic Rankine Cycle heat converter – which is also running a turbine, but using another medium than steam. In most systems, the mechanical energy will be converted to electric energy before it is eventually merged with other energy producers onboard. The drawback with all such solutions is that only a minor part of the heat energy can be converted (usually less than 10 % of the available heat energy), at a high cost. Furthermore, the heat recovery is only most effective when the engine is running at full or near full load. Generally the two-stroke engines used on bulk carriers have a high efficiency compared to other type’s internal combustion engines. As long as one does not change the type of engine completely, the main engine fuel saving measures consists in reducing the engine SFOC: •

De-rating of the main engine

•

Use of electronically controlled engine for engine control tuning

•

Low load optimization by use of variable turbine area

•

Low load optimization by use of exhaust gas bypass

Compatibility Engine tuning is compatible with all flow modifying devices.

5.12.2 De-rating of main engine The thermal efficiency of an engine increases when the ratio between the mean effective pressure and maximum pressure increases. De-rating an engine will impact this ratio, Page 53 of 84


which will potentially reduce the SFOC by up to 4,3% compared to a engine installed at its nominal rating /22/.

Figure 17 Relative fuel consumption in normal service of different derated main engines for a 75,000 dwt Panamax product tanker at 15 knots. From /22/.

5.12.3 Use of electronically controlled engine for engine control tuning This measure enables the engine to be further optimized for its trading pattern, particularly if one expects to operate a larger portion of the time on part loads or low loads. Electronically controlled engines are becoming standard for most newbuildings. These types of engines allows for continuous optimization and control of key engine parameters. In addition the engine may be tuned for part loads or low loads, which gives lower SFOC for loads below 70-85% SMCR. Depending on the trading pattern the engine may be optimized for either part load or low load.

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Figure 18 Example of SFOC reductions for a MAN B&W 6S80ME-C8.2 with ECT. From /31/.

5.12.4 Part load or low load optimization by use of variable turbine area or exhaust gas bypass An alternative to ECT for optimization for part loads or low loads is to use a variable turbine area exhaust gas bypass. The aim of these measures is also to reduce the SFOC at loads below 70-85% of SMCR. Variable turbine area allows the turbocharger to be tailored for a larger range of loads, giving the engine lower SFOC at part loads or low loads. Exhaust gas bypass (EGB) is tailored for each engine and allows for exhaust gas bypass when the engine operates at lower loads. This will reduce the SFOC of the engine at part loads and low load. These features may be installed on both mechanically controlled engines and electronically controlled engines, but the benefits will be higher for electronically controlled engines.

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Figure 19 Example of benefits of variable turbine (VT) for electronically controlled engines. From /31/.

Figure 20 Example of benefits of variable turbine (VT) for mechanically controlled engines. From /31/.

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Figure 21 Example of benefits of exhaust gas bypass (EGB). From /31/.

Note, however, that the common feature for all above items (Figure 18 to Figure 21) is that there is an optimal point where the engine is performing most efficiently, and that even small deviations from this point gives a large penalty in the form of reduced efficiency.

5.12.5 Requirements from classification The engine is approved for a specific RPM and MCR. As long as adjustment of the electronic control is not changing radically the rating of the engine, any engine tuning is allowed by Class. Special attention has to be put into the documentation of NOx emissions; the engine tuning should not lead to an increase of these emissions.

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5.13 Auxiliary engine 5.13.1 Physical description Auxiliary engines onboard bulk ships that are not geared usually are mainly supplying electrical power to the accommodation and machinery systems when underway. The most common setup for auxiliary engines is to have three auxiliary engines of the same size. This allows for one engine to be out for maintenance while still complying with requirements for redundancy. Generally all the measures that may be applied for the main engine in order to reduce the SFOC may be applied to the auxiliary engines. The relative savings may however be larger if the auxiliary engines operate a larger part of their time at part loads or low loads. An alternative to an auxiliary engine is to replace one auxiliary engine by a shaft generator. Since most bulk carriers operate with FPP, the shaft generator would need to be fitted with frequency control. Compatibility Shaft generators are compatible with all flow modifying devices, as well as main engine tuning.

5.13.2 Requirements from classification The installation of the generator on the shaft should not change the operating mode of the engine and the propeller: special attention has to be put on the connection between the generator and the propeller shaft, as well as all the new components installed in the driveline. The generator itself needs to fulfill specific requirements to electronic equipment, e.g in terms of insulation and temperature rise. See for example DNV Rules for Ships Part 4, Chapter 8, Section 5.

5.13.3 Range of expected fuel savings Shaft generators would benefit from the fact that most main engines will have a SFOC that is approximately 10-15 g/kWh lower then a conventional auxiliary engine.

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5.14 Waste heat recovery system 5.14.1 Physical description Examples of waste heat recovery (WHR) system components are • Turbo generators • Steam generators • Combined systems

Figure 22 Power concept for a waste heat recovery system. From /32/.

WHR has the largest potential for efficiency improvement for the traditional two-stroke engines, but there are challenges related to exploiting this potential. Both the complexity of the system and cost has made these types of systems rare on bulk carriers. WHR consists of exhaust gas boiler(s), steam turbine generators, turbo generators, gear and electrical generator. Depending on the size of the engine and complexity of the WHR system one would either use only a steam turbine or a combination of exhaust turbine and steam turbine. Combing exhaust turbine and steam turbine will increase the efficiency of the system, but also contributes to the complexity of the system. The output from a waste heat recovery system is electrical power, which may be used onboard the ship. Bulk carriers have modest electrical power consumption when underway and a WHR may therefore be able to completely replace an auxiliary engine. If the WHR system produces more electrical power than what is required onboard the ship there is no fuel saving above this level. An alternative if one has a very efficient WHR system is to install a power intake on the main shaft. Page 59 of 84


Compatibility WHR devices are compatible with all flow modifying devices, as well as main engine tuning.

5.14.2 Requirements from classification The WHR should not interfere with the power plant of the ship. As long as the loss of heat through the recovery process is not threatening the safe operation of the boilers, turbo chargers and engines of the ship, the WHR can be operated.

5.14.3 Range of expected fuel savings A waste heat recovery system will have varying efficiency and output depending on engine type, size and load. Depending of the complexity of the system and type of engine the output from a WHR will range from 3,7% to 7,8% of ME output for engine sizes applicable for bulk carriers /32/.

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6.

Comparison of fuel saving measures including compatibility

This chapter presents a comparison of the different fuel saving measures including typical gains in efficiency or reduction of resistance, physical effects and compatibility. The following references include a comparison of series of fuel saving measures: - IMO 2009 /28/ - IMarEST 2010 /29/ - ITTC 1990, The propulsion committee, page 125 /12/ - Stierman 1986, page 188 /11/. Also considers on which propulsive coefficients the different devices have effect. - ITTC 1999, page 8 /7/ - Ship propulsion solutions, /13/ - HSVA 2006, page 4, /9/ - HSVA 2008, page, 6, /14/ - Mewis 2010, page 22, /1/ - HSVA, 2009, page 127 in pdf, /15/ Table 15. Estimated fuel savings for different fuel saving measures on bulk carriers.

Fuel saving measure

Savings in % power 5-8

Cost in kUSD

Comment

170 -290 dep. on ship size 210 Panamax 290 Capesize

Propeller boss cap fin

2-4

67 – 170 dep. on ship size 67 Handysize 179 for 205K DWT

Design cost of Model tests USD 140 000 / and CFD. series Full-scale trials Design cost of Model tests USD 72 000 / and CFD series

Pre swirl stator

3-5

Design cost of USD 85 000 / series

Propeller nozzle Contra rotating propeller

0-7

50-85 dep. on ship size 50 Handysize 85 for 205K DWT Highly variable

2-14

Very high cost

Complex system, requires different machinery setup

Propeller rudder transition bulb Rudder

2-4

160 for Costa bulb combined with twisted spade rudder

1-3

No additional price unless

Mewis duct

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Means of validation

Model tests and CFD


profile patent profile is used Table 16 sums up the individual comments on compatibility. The general idea is that two devices modifying the flow the same way are not compatible. In addition, two devices located very close to each other are usually reducing their respective efficiency. Finally, any device located upstream will influence the inflow to the other downstream devices.

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P

N C P

N N N N

P N N N P

P C N N

P N P

N C

N

C

C

C

C

C

P N P C N

Rudder profile

N P

Contra rotating propeller

Propeller nozzle

Mewis duct Propeller boss cap fin Pre swirl stator Propeller nozzle Contra rotating propeller Propeller rudder transition bulb Rudder profile

Pre swirl stator

Mewis duct

C – fully compatible N – should not be combined P – partly compatible

Propeller boss cap fin

Compatibility

Propeller rudder transition bulb

Table 16. Matrix showing compatibility between different fuel saving devices.

C C C C C C

C


7. /1/ /2/

/3/ /4/ /5/ /6/

/7/ /8/ /9/ /10/ /11/ /12/ /13/ /14/ /15/

/16/ /17/ /18/ /19/ /20/

/21/ /22/ /23/

References Friedrich Mewis, (2010), Mewis Duct, Presentation at Rostock University January 29th The International Fund for Animal Welfare (IFAW), (2009), ”Reducing underwater noise pollution from large commercial vessels”, Renilson Marine Consulting Pty Ltd., http://www.ifaw.org/Publications/Program_Publications/Whales/asset_upload_file262 _53989.pdf www.shippropulsionsolutions.com Ship Propulsion Solutions, LLC, Lexington, KY, USA Mewis, F., Hollenbach, U., (2006), Special Measures for Improving Propulsive Efficiency, HSVA NewsWave, the Hamburg Ship Model Basin Newsletter, 2006/1 Gearhart, W. S., McBride, M. W., (1989), Performance Assessment of Propeller Boss Cap Fin Device, 22nd ATTC, St John’s, Newfoundland Ouchi, K., (1989), Research and Development of PBCF )Propeller Boss Cap Fins) – Improvement of Flow from Propeller Boss, Proceedings of the International Symposium on Ship Resistance and Powering Performance ’89 (ISRP), Shanghai 22nd ITTC, (1999), “The specialist committee on unconventional propulsors”, final report Oosterveld, M. W. C., (1970), “Wake adapted ducted propellers”, Publication no. 345, Netherlands ship model basin, Wageningen, Netherlands. HSVA, (2006), “News wave”, The Hamburg Ship Model Basin newsletter 2006/1. Wärtsilä, (2011), “ENERGOPAC”, www.wartsila.com. Stierman, E. J., (1986), ”Energy saving devices, literature review”, Maritime Research Institute Netherlands, Report No. 47434-1-RT, August. ITTC, (1990), “Report of the propulsor committee”, ITTC. Ship Propulsion Solutions, (2011), “Stern appended ship energy saving devices: types and combinations”, http://shippropulsionsolutions.com/pdfs/esd-comparisons.pdf HSVA, (2008), “News wave”, The Hamburg Ship Model Basin newsletter 2008/2. Hollenbach, U., (2009), “Optimizing hull forms for desing- and “off-design” – conditions”, HSVA, Fuel management, ship performance and energy efficiency, Lloyd’s maritime academy. Wärtsila, Ir. A.A.M. Voermans, Fuel savings by means of upgrading ship propulsion system, Presentation held in Götebörg March 2006 ITTC, (2008), “Quality system manual”, http://ittc.sname.org/new%20recomendations/ITTC%20Contents.pdf Ghassemi, H., (2009), “Hydrodynamic performance of coaxial contra-rotating propeller (CCRP) for large ships”, Polish maritime research, 1 (59) 2009 Vol. 16, pp. 22-28. Proceé, R. F., (2009), “Comparison of Nox-reducing technologies”, MAN, Nox-fond seminar, January 21st, Trondheim. Min, K.-S., (2009), “Study on the contra-rotating propeller system design and full-scale performance prediction method”, Inter J Nav Archit Oc Engng, 1, pp. 29-38, DOI: 10.3744/JNAOE.2009.1.1.029. MAN B&W, “Basic principles of ship propulsion”, MAN, http://www.manbw.com/files/news/filesof3859/P254-04-04.pdf. MAN Diesel Turbo, “How to Influence CO2”, MAN, http://www.mandieselturbo.com/files/news/filesof15013/5510-0083-00ppr_low.pdf Grontmij / Carl Bro, (2009) “35000 dwt bulk carier exhaust gas emission reduction

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/24/

/25/

/26/ /27/ /28/ /29/

/30/

/31/

/32/

8.

concept study”, http://www.greenship.org/fpublic/greenship/ Svardal, Jan and Mewis, Friedrich, (2009), “Cost Savings by Hydrodynamic Measures”, Ship Efficiency conference, Hamburg, http://www.shipefficiency.org/onTEAM/pdf/Mewis.pdf Svardal, Jan and Mewis, Friedrich, (2009), “Cost Savings by Hydrodynamic Measures”, Ship Efficiency conference, Hamburg, PDF of presentation: http://www.ship-efficiency.org/onTEAM/pdf/Svardal_Mewis_ppt.pdf Brix, J, (1993), “Manoeuvring Technical Manual”, Seehafen Verlag Gmbh, Hamburg Fathom, (2011), “Ship Efficiency: The Guide”, Editors: Peter Lockley and Alison Jarabo-Martin, www.fathomshipping.com IMO, (2009), “Second IMO GHG Study 2009” IMarEST, (2010), “Reduction of GHG emissions from ships - Marginal abatement costs and cost-effectiveness of energy-efficiency measures”, IMO document MEPC61/INF. 18, 23 July 2010 Friedrich Mewis, (2009), A Novel Poewer-Saving Device for Full-form Vessels, First International Symposium on Marine Propulsors SMP 09, Trondheim, Norway, June 2009 MAN Diesel Turbo (2010), SFOC optimization Methods, For MAN B&W Two-stroke IMO Tier II Engines, http://mandieselturbo.com/files/news/filesof15180/5510-009900ppr_low.pdf MAN Diesel Turbo (2010), TCS-PTG, Savings with extra power, http://www.mandieselturbo.net/tcbrochures/data/TCSPTG%20Savings%20with%20Extra%20Power.pdf

Disclaimer

"The Guideline for the Fuel Saving Devices and the Return of Investment Calculator (the "SDARI and DNV Products")are developed by SDARI and DNV and provided to our clients free of charge. We have taken all reasonable care in the development of the SDARI and DNV Products, but SDARI / DNV cannot guarantee that the SDARI and DNV Products will function error free or that estimated fuel savings will be met. Therefore, SDARI and DNV disclaim any responsibility, liability and consequences in relation to the use of the SDARI and DNV Products."

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Appendix: 1 USER GUIDE RETURN ON INVESTMENT TOOL

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1. User Guide 1.1 General Use the password: “DNVSDARI” to use the ROI Tool This return on investment tool is created in Microsoft Excel 2003 and has not been tested for other versions of Excel.

1.2 Content The ROI tool consists of several worksheets with different tab colours: -

Orange colour indicates sheets which require inputs Green coloured sheets are calculating and showing the financial results Blue coloured sheets contain useful bulk carrier information White coloured sheets contains information about the tool

Editable input cells do either have white or lightblue background colour. Values entered into the white coloured cells are used in calculations while lightblue cells are only for informational purposes.

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1.2.1 Workbook protection and macros Only lightblue and white coloured cells are editable in the tool. All other cells are locked with a password and will not be possible to edit. Column width may however be changed in the “Cashflow” sheet. Also note that the worksheets make use of macros to achieve their functionality, and so must have Macros Enabled in order to function correctly!

1.2.2 Tips and notes Throughout the tool you will find tips and notes that could be useful. These notes do not appear on printouts.

1.2.3 Print In addition to the common Excel printing features it is possible to print out a complete report by pushing the “Print Report” button that is found on the top of the “Project data” worksheet. All sheets will then be adjusted to be print friendly. If some charts or content for some reason are not printed as wanted, it is possible to adjust printer settings through the usual Excel print features. All notes, tips, and buttons are removed in printouts.

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1.3 Guidelines In the following sections the different sheets found in the tool are explained.

1.3.1 Project data

The “Project data” sheet contains optional inputs which are for pure informational purposes. The values do not have any effect on any of the calculations, but some inputs are useful when deciding other inputs which have an effect on the investment analysis.

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1.3.2 Fuel saving measure

In this sheet the main input fields are found. Fuel saving measure is selected at the top and the corresponding costs are stated. Investment cost is a required input while maintenance cost and re-sale impact are optional. See the Guideline document section 5 for relevant input data. The selection of fuel saving measure at the top does not effect any calculations, but are used in titles in charts throughout the tool. The investment scenario is defined through the investment period, discount rate and a fuel price. Select a predefined heavy fuel oil (HFO) price development scenario or enter a fixed fuel price to use in the calculations. To edit the fuel price scenarios go to the sheet named "Fuel price scenario". The selected investment period also changes the scale of the x-axis’ in most of the charts. The two charts in this worksheet are also found in the “Cost Benefit” sheet, thus they will not appear in printouts.

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1.3.3 Operating profile

Bulker size and speed are only for informational purposes and does not have any effect on calculations. The operating profile could contain maximum 5 operating states, e.g. sailing laden, cargo handling. It is however not necessary to fill out all operating states, but at least one is required. The operating states are defined by a name, a speed, number of days and the excepted fuel reduction for this state. The speed and name of the states are optional and do not need to be selected/given. There are two ways of calculating the fuel consumption. It could be calculated based on installed engine power, specific fuel consumption (SFOC) and average engine load (%MCR) or it could be entered directly as ton/day without any calculations. Some common fuel consumption data is found in the sheet named "Vessel data" for guidance. Only the selected fuel consumption alternative is used in the calculations. If total days are below 365 days, the fuel consumption is assumed to be zero in the remaining days, and if the total days are more than 365 a red background colour will appear. Note that the average fuel consumption numbers stated to the right in the figure do not include the fuel reductions due to the applied fuel saving device.

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The y-axis value type varies for chart to the right depending on which fuel consumption alternative chosen. For alternative 1 it is % MCR and for alternative 2 it is ton/day.

1.3.4 Fuel price scenario

The “Fuel price scenario” sheet contains the three fuel price development scenarios and one custom scenario. These scenarios’ may be edited. In order to evaluate fuel price sensitivity or use a fuel price development in the calculations it is necessary to fill out these fields.

1.3.5 Cost benefit Main results related to fuel consumption, fuel savings and financial measures are found in the “Cost Benefit” sheet.

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If the time horizon and payback period is very short, the most relevant financial measures will be the ones within the red circle (and perhaps the IRR). If the initial cost is higher and considered to be a long-term investment, it would be more relevant to evaluate the financial metrics within the blue circle which are considering the time value of money.

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1.3.6 Sensitivity analysis

Sensitivity to fuel price and sensitivity of changes in initial investment cost could be evaluated in this sheet. Use the scrollbar to change initial investment and to evaluate the implications on the cash flow. Changes only apply to the two charts at the bottom. If the investment period is quite long (typically above 10 years) it could be useful to resize the charts by pushing the “Resize charts” button at the top of the sheet.

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1.3.7 Emissions

In this sheet it is possible to estimate the reductions in CO2, SOx, NOx and particle matters (PM) due to the fuel saving device. The emissions factors used to calculate the reductions could be changed, and some guidance values are found in the “Vessel data” sheet

1.3.8 Cash flows The detailed cash flows for the different scenarios are found in the “Cash flows” sheet.

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The number of years shown is controlled by the selected "Investment period" in sheet named "Fuel saving measure". Select an investment period with a higher value (longer time period) to view the cash flow for a longer period.

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Appendix: 2 METHODOLOGY RETURN ON INVESTMENT TOOL

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1. Methodology This chapter describes how the return-on-investment (ROI) tool is built up and the process steps needed to perform what is referred to as a return of investment analysis or costbenefit analysis. In a cost-benefit analysis (CBA) all costs and benefits are adjusted for the time value of money by using a discount rate, so that the future projected costs and benefits (revenues) are expressed on a common basis in terms of their present value (PV). This is often referred to as the discounted cash flow method (DCF) and is preferably used to appraise long-term investment projects.

1.1 Objective The objective is to describe an approach to evaluate the cost-effectiveness of different fuel saving measures/devices.

1.2 Assumptions When evaluating a fuel saving measure all the costs and benefits should be considered. However, this method focuses primarily on covering the most important economical changes due to the fuel saving devices, which is considered to be the following: Costs - Initial investment - Annual maintenance cost

Benefits - Fuel savings - Increased resale value - Reductions in CO2, NOx, and SOx emissions

1.3 Model The proposed methodology to evaluate cost-effectiveness is presented in the figure below.

The starting point is that a user (ship owner) wants to analyse the cost-benefit of a fuel saving device listed in the introduction (e.g. pre-swirl stator) applied to a particular bulk carrier design.

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1.3.1 Fuel saving measure & estimated costs The first step in the process is to estimate costs due to the fuel saving measure. The initial investment cost, the annual increase in maintenance cost and if relevant the re-sale increase value are given as inputs. Some measures are quite costly and might have an impact on the second-hand value of the vessel; this must also be taken into consideration. The outputs from this process are the main inputs to the investment calculations.

1.3.2 Operating profile & fuel consumption The second step is to estimate the fuel consumption without the fuel saving device installed. This is done by defining a relevant operating profile for the vessel. Appropriate operating states such as sailing loaded and sailing ballast are defined, and the annual operating days in each state are estimated. For each operating state (maximum 5) the estimated fuel reduction potential in percentage is given as input. The normal fuel consumption without the fuel saving device applied is either specified for each operating state directly in tonnes per day, or it could be calculated based on detailed engine data. For the latter approach the following data must be defined: -

average engine load in percentage of maximum installed power (% MCR), average specific fuel oil consumption (SFOC)

and the amount of installed engine power must also be given. The daily fuel consumption for each operating state is then calculated as follows: Tonnes per day = Average engine load [kW] x Average sfoc [g/kWh] x 24 hours x 1.000.000

1.3.3 Financial scenario & fuel price development When the costs have been calculated and the annual fuel consumption and fuel reductions are estimated, the financial scenario is to be defined. A discount rate and an investment period must be set. The fuel oil price is either stated as a fixed price throughout the whole investment period or based on a forecasted fuel price development which varies over the investment period. These inputs define the risk willingness/aversion when evaluating the financial aspects of the fuel saving measure. A high, medium and low fuel oil price scenario is also defined to be used for sensitivity analysis.

1.3.4 Fuel savings and cost-benefit of fuel saving measure Together the outputs from the previous processes give the necessary inputs to calculate the fuel savings, and to set up a net cash flow and a discounted cash flow (DCF). Common financial metrics should than be evaluated before a decision to invest is made, see chapter 3 for a brief description of the different financial metrics available. Based on the fuel savings reductions in air emissions (CO2, NOx, SOx, PM) due to the fuel savings may also be estimated.

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1.3.5 Sensitivity With all costs and benefits identified, uncertainties and sensitivities should be assessed to evaluate the robustness of the investment. Variations in fuel price and sensitivity with respect to changes in the investment cost could be evaluated as well as the net present value profile, indicating sensitivity to changes in the discount rate.

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2. Financial METRICS Many formal methods can be used in capital budgeting or investment appraisals. Research published in the Journal of Financial Economics 2001 showed that most of U.S. companies follow academic theory and use discounted cash flow (DCF) and net present value (NPV) to evaluate new projects.

Source: Journal of Financial Economics, Vol. 60 (2001).

The top 5 techniques used by chief financial officers (CFO) were:

-

Internal rate of return (IRR) Net present value (NPV) Return on investment (ROI) threshold (also known as the hurdle rate) Payback Sensitivity analysis

All of these are covered in the ROI tool, and in the following sections the different financial metrics are briefly explained.

2.1.1 Return on investment Description The term Return on Investment (ROI) is commonly used in different ways and what that is included in such a calculation varies. Business literature commonly rather recommends focusing on financial metrics such as net cash flow, discounted cash flow (net present value), IRR, and payback period instead of calculating the “simple” resulting amount divided by initial amount without considering the time value of money. The ROI measure could be based on the net cash flow without considering the time value of money (most common!) or based on the discounted cash flow. Both are calculated in the tool. The discounted ROI is calculated in the following way in the tool: ROI = PV future cash flow – Initial investment Initial investment Page 80 of 84


Decision criteria •

Accept if ROI > minimum acceptable rate of return (also known as hurdle rate)

2.1.2 Net Present Value (NPV) Description When all the costs and incomes in the cash flow are discounted to its present value and are added together, the result is called the Net Present Value (NPV). The present value of an investment's future net cash flows minus the initial investment: NPV = PVfuture cash flows - inital cost at t = 0 Decision criteria • •

Independent project: Accept if NPV ≥ 0 Mutually exclusive projects: Accept project with highest NPV ≥ 0

2.1.3 Internal Rate of Return (IRR) Description Instead of proposing of discount rate and finding the NPV, it is possible to find the discount rate that produces a NPV = 0. This discount rate is what is known as the internal rate of return (IRR). Decision criteria In general, the higher the IRR, the better the returns relative to cost are, and the lower the risk is. • •

Independent projects: Accept if IRR > OCC (opportunity cost of capital) Mutually exclusive projects: Accept project with highest IRR > OCC (if the projects are the same size)

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2.1.4 Payback period Description Payback period is the time required for an investment to recover its cost. The annual cash flows are used to determine the payback period. It could be based on the net cash flow or discounted cash flow (not mixed), and both are calculated in the ROI tool. Decision criteria • •

Independent projects: Accept if payback > ROI threshold Mutually exclusive projects: Accept project with shortest payback > threshold

2.1.5 Profitability index Description Profitability index is the ratio of payoff to the investment of a proposed project. It is a useful measure for ranking, because it quantifies the amount of value created per unit of investment. PI = PV future cash flows Initial investment (As described previously a discounted ROI is calculated quite similarly, except that the initial investment is subtracted in the numerator) Decision criteria • •

Independent projects: Accept if PI ≥ 1 Mutually exclusive projects: Accept project with highest PI ≥ 1

- o0o -

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For further information, please contact: SDARI Please Contact Mr. Zhou Zhiyong at R&D Department [email protected] DNV Please contact your local customer service manager or unit for Ship Hydrodynamics [email protected]

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Guideline for Fuel Saving Measures on Bulk Carriers

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