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Marine, Offshore and Engineering Consultants TECHNICAL NOTE
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Bluewater Energy Services
[email protected]
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Attn.
Kees van Beveren
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[email protected] Jason Bell
Pages
6
Date
Reference
25 Jun 2013 TN_24138_1
Haewene Brim Bollard Pull Calculations
Subject
Introduction
Global Maritime Scotland Ltd (GM) has been requested by Bluewater Energy Services (BES) to carry out a bollard pull calculation for the Haewene Brim FPSO. The scope of work and deliverables d eliverables are detailed in proposal P13854 Ref[1]. The calculations are based on DNV Rules for Planning and Execution of Marine Operations Ref[2], DNV RP-H103 Ref[3] and DNV OS-C301 Ref[4]. BES has informed GM that the contracted tow tug is i s the BB Troll with bollard pull of 165 tonnes. Requirements
As per Ref[2] the towing force requirement for open sea is to be sufficient to maintain zero speed under the environmental conditions shown in Table 1. Environmental Condition Wind Velocity (Vw) Head Current Velocity (Vc) Significant Wave Height (Hs)
Value 20 m/s 1 m/s 5m
Table 1: Environmental Conditions
Ref[2] also states that for coastal tows in narrow or shallow waters the bollard pull shall be sufficient to maintain a speed over ground of 2 knots under defined environmental conditions. The environmental conditions here will conservatively be taken as those stated in table 1. Environmental Force Calculations
The three main environmental forces required for the bollard pull calculation are Wind, Current and Wave Drift forces. The equations for calculating these forces are detailed in Ref[3] and[4] and summarised as follows:
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Wind Force The formula for the wind force is shown below:
�
� ∗ ∗ ∗ ∗ ∗
Where: Fw = Wind force [tonnes] Cs = Shape coefficient Ch = Height coefficient 3 ρ = Density of air [t/m ] V = Wind velocity [m/s] 2 A = Projected area of all exposed surfaces [m ] 2 g = Gravity [m/s ]
Current Force The formula for calculating the current force is shown below:
�
� ∗ ∗ ∗ ∗
Where: Fc = Current force [tonnes] 3 ρ = Density of water [t/m ] C = Current force coefficient V = Current velocity [m/s] 2 A = Wetted surface area of hull [m ] 2 g = Gravity [m/s ]
Wave Drift Force The formula for wave drift force is shown below: �
∗ ∗ ∗ ∗
Where: Fwd = Wave drift force [tonnes] 3 ρ = Density of water [t/m ] R = Reflection coefficient B = Breadth of towed object Hs = Significant waveheight [m]
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Projected Areas
Wind and current loading areas have been measured using a forward profile drawing of the vessel, supplied by BES, at a tow draught of 7m. A projected wind and current area drawing is shown in Appendix B. Bollard Pull
The required bollard pull to maintain zero speed under the environmental conditions stated in Table 1 is calculated as 117 tonnes. This includes a tug efficiency factor of 0.75 as recommended for offshore tows in Ref[2]. An additional check with the vessel towed at a speed of 2 knots has been performed. Conservatively the environmental conditions stated in Table 1 are also adopted here. The required bollard pull here is calculated at 149 tonnes . The bollard pull calculation spreadsheet is included in Appendix A. Conclusion
The calculations show that the BB Troll has sufficient bollard pull capacity to satisfy the DNV code requirements for the Haewene Brim tow operation.
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References
[1] [2] [3] [4]
GM Proposal P13854 Haewene Brim Bollard Pull Calculations, June 2013. DNV Rules for Planning and Execution of Marine Operations, 1996 Revision, January 2000. DNV RP-H103 Modelling and Analysis of Marine Operations, April 2011. DNV-OS-C301 Stability and Watertight Integrity, DNV, April 2011.
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APPENDIX A
Bollard Pull Calculation Spreadsheet
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BOLLARD PULL CALCULATIONS VESSEL NAME:
Haewene Brim
BEAM DRAUGHT LENGTH DEPTH
42.00 7.00 252.00 20.50
m m m m 3
ϱair
0.00122 tonnes/m
ϱwater
1.025 tonnes/m
g (acceleration)
3
2
9.81 m/s
Wave Drift Coefficients From DNV RP-H103 April 2011 Table 7-1 Typical reflection Coeffircients
1) Wave Drift Force R Hs WAVE DRIFT FORCE =
0.45 5.00
DNV Marine Ops Pt.2 Ch. 2 Sect. 3.3.2.4
27.24 tonnes
DNV RP-H103 Sect. 7.2.6.4
"R"
Square Face Condeep Face Vertical Cylinder Barge with Raked Bow Barge with Spoon Bow Ship Bow
1.00 0.97 0.88 0.67 0.55 0.45
Wind Coefficients
2) Wind Force WIND SPEED
From DNV OS-C301 April 2011 Table B1 Values Wind Force Shape Coefficient (Cs) Shape Spherical 0.4 Cylindrical 0.5 Large flat surface (hull, deckhouse, smooth under-deck areas) 1.0 Drilling derrick 1.25 Wires 1.2 Exposed beams and girders under deck 1.3 Small parts 1.4 Isolated shapes (crane, beam, etc.) 1.5 Clustered deckhouses or similar structures 1.1
20.00 m/s
AREA (Hull MSL to 15.3m) Cs Ch
641.94 1.00 1.00
m^2
Hull and Main Decks (15.3 to 30.5m) Cs Ch
619.86 1.00 1.10
m^2
Deckhouse (30.5 to 46m) Cs Ch
274.30 m ^2 1.10 1.20
Deckhouse surr. Structure (30.5 to 46m) Cs Ch
38.32 1.10 1.20
m^2
Equipment on Deckhouse (30.5 to 46m) Cs Ch
26.06 1.40 1.20
m^2
Equipment on Deckhouse (46 to 61m) Cs Ch
19.54 1.40 1.30
m^2
Flare Towers (30.5 to 46m) Cs Ch
23.03 1.25 1.20
m^2
Flare Towers (46 to 61m) Cs Ch
65.37 1.25 1.30
m^2
Flare Tower (61 to 76m) Cs Ch
41.27 1.25 1.37
m^2
Exhaust Towers (30.5 to 46m) Cs Ch
71.52 1.00 1.20
m^2
WIND FORCE =
52.64
tonnes
Cs 0.40 0.50 1.00 1.25 1.20 1.30 1.40 1.50 1.10
Table B2 Values Wind Force Height Coefficient (Ch) Height above sea level (metres) 0 - 15.3 15.3 - 30.5 30.5 - 46.0 46.0 - 61.0 61.0 -76.0 76.0 - 91.5 91.5 - 106.5 106.5 - 122.0 122.0 - 137.0 137.0 - 152.5 152.5 - 167.5 167.5 - 183.0 183.0 - 198.0 198.0 - 213.5 213.5 - 228.5 228.5 - 244.0 244.0 - 256.0 Above 256 Current Coefficients Hull Type SPOON BOW / FAIRED STERN SPOON BOW / RAKED STERN RKD BOW / RKD/SQU STERN
Ch 1.00 1.10 1.20 1.30 1.37 1.43 1.48 1.52 1.56 1.60 1.63 1.67 1.70 1.72 1.75 1.77 1.79 1.80
Cd 0.20 0.35 0.50
DNV-OS-C301Section B 100
3) Current/Speed Force VESSEL/ CURRENT SPEED Cd BOW AREA
CURRENT FORCE =
1.00 m/s 0.50 292.74 m^2
7.65 tonnes
DNV RP-H103 Sect. 3.2.4
4) Bollard Pull Static Bollard Pull
Required Bollard Pull (with tug efficiency of 0.75)
Global Maritime
87.53 tonnes
116.71 tonnes
Filename: Haewene Brim BP Calc (updated 24.06.13)
Page: 1
BOLLARD PULL CALCULATIONS VESSEL NAME:
Haewene Brim
BEAM DRAUGHT LENGTH DEPTH
42.00 7.00 252.00 20.50
m m m m
ϱair
0.00122 tonnes/m
3
ϱwater
1.025 tonnes/m
3
g (acceleration)
2
9.81 m/s
Wave Drift Coefficients From DNV RP-H103 April 2011
Table 7-1 Typical reflection Coeffircients
1) Wave Drift Force R Hs WAVE DRIFT FORCE =
0.45 5.00
DNV Marine Ops Pt.2 Ch. 2 Sect. 3.3.2.4
27.24 tonnes
DNV RP-H103 Sect. 7.2.6.4
"R"
Square Face Condeep Face Vertical Cylinder Barge with Raked Bow Barge with Spoon Bow Ship Bow
1.00 0.97 0.88 0.67 0.55 0.45
Wind Coefficients
2) Wind Force WIND SPEED
From DNV OS-C301 April 2011 Table B1 Values Wind Force Shape Coefficient (Cs) Shape
20.00 m/s
AREA (Hull MSL to 15.3m) Cs Ch
641.94 m^2 1.00 1.00
Hull and Main Decks (15.3 to 30.5m) Cs Ch
619.86 1.00 1.10
Deckhouse (30.5 to 46m) Cs Ch
274.30 m^2 1.10 1.20
m^2
Deckhouse surr. Structure (30.5 to 46m) Cs Ch
38.32 m^2 1.10 1.20
Equipment on Deckhouse (30.5 to 46m) Cs Ch
26.06 m^2 1.40 1.20
Equipment on Deckhouse (46 to 61m) Cs Ch
19.54 m^2 1.40 1.30
Flare Towers (30.5 to 46m) Cs Ch
23.03 m^2 1.25 1.20
Flare Towers (46 to 61m) Cs Ch
65.37 m^2 1.25 1.30
Flare Tower (61 to 76m) Cs Ch
41.27 m^2 1.25 1.37
Exhaust Towers (30.5 to 46m) Cs Ch
71.52 m^2 1.00 1.20
WIND FORCE =
52.64
Cs
Spherical 0.4 Cylindrical 0.5 Large flat surface (hull, deckhouse, smooth under-deck areas) 1.0 Drilling derrick 1.25 Wires 1.2 Exposed beams and girders under deck 1.3 Small parts 1.4 Isolated shapes (crane, beam, etc.) 1.5 Clustered deckhouses or similar structures 1.1 Table B2 Values Wind Force Height Coefficient (Ch) Height above sea level (metres) 0 - 15.3 15.3 - 30.5 30.5 - 46.0 46.0 - 61.0 61.0 -76.0 76.0 - 91.5 91.5 - 106.5 106.5 - 122.0 122.0 - 137.0 137.0 - 152.5 152.5 - 167.5 167.5 - 183.0 183.0 - 198.0 198.0 - 213.5 213.5 - 228.5 228.5 - 244.0 244.0 - 256.0 Above 256
0.40 0.50 1.00 1.25 1.20 1.30 1.40 1.50 1.10
Ch 1.00 1.10 1.20 1.30 1.37 1.43 1.48 1.52 1.56 1.60 1.63 1.67 1.70 1.72 1.75 1.77 1.79 1.80
Current Coefficients
tonnes
Hull Type SPOON BOW / FAIRED STERN SPOON BOW / RAKED STERN RKD BOW / RKD/SQU STERN
Cd 0.20 0.35 0.50
DNV-OS-C301Section B 100
3) Current/Speed Force VESSEL/ CURRENT SPEED Cd BOW AREA
CURRENT FORCE =
2.03 m/s 0.50 292.74 m^2
31.47 t onnes
2 knots vessel speed + 1 m/s current
DNV RP-H103 Sect. 3.2.4
4) Bollard Pull Bollard Pull
111.36 tonnes
Required Bollard Pull (with tug efficiency of 0.75)
148.48 tonnes
Global Maritime
Filename: Haewene Brim BP Calc (updated 24.06.13)
Page: 1
APPENDIX B
Projected Areas
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