wave buoy mooring design evaluation

Wave Buoy Mooring Design Evaluation

Prepared by: Randolph Kashino AXYS Technologies Head Office 2045 Mills Road Sidney, British Columbia Canada PWGSC Contract Number: W7701-4501464898 Technical Authority: Eric Thornhill, Defence Scientist Contractor’s Publication Date: September 2016

The scientific or technical validity of this Contract Report is entirely the responsibility of the Contractor and the contents do not necessarily have the approval or endorsement of the Department of National Defence of Canada.

Contract Report

DRDC-RDDC-2017-C064

May 2017

Template in use: (2010) SR Advanced Template_EN (051115).dotm

© Her Majesty the Queen in Right of Canada, as represented by the Minister of National Defence, 2016

© Sa Majesté la Reine (en droit du Canada), telle que représentée par le ministre de la Défense nationale,

2016

Wave Buoy Mooring Design Evaluation For Defense Research and Development Canada – Atlantic Research Centre (DRDC-ARC)

Final Report September 27, 2016

Prepared by

Randolph Kashino

AXYS Technologies

Head Office European Office 2045 Mills Road Esplanadestraat 1 Sidney, British Columbia 8400 Oostende Canada Belgium

www.axystechnologies.com

http://www.axystechnologies.com/

3

Contact Author Reviewed Randolph Kashino First name Last name +1 250 655 5862 Telephone number [email protected] Email address

Revision History Rev Date Change By 00 2016/09/27 Draft RKK

01 2017/04/18 Final – Confidentiality Statements Removed

RKK

02 2017/05/11 Final – revised Appendix RKK

4

Table of Contents

1. Mooring Simulation Tasks ..................................................................................................................... 8 Sea State Conditions to Simulate: ............................................................................................................. 8

2. WHOI CABLE Program ......................................................................................................................... 13

3. Simulations .......................................................................................................................................... 14 3.1. Simulation 5.1.1 .......................................................................................................................... 14 3.2. Simulation 5.1.2 .......................................................................................................................... 18 3.3. Simulation 5.1.3 .......................................................................................................................... 22 3.4. Simulation 5.1.4 .......................................................................................................................... 26 3.5. Simulation 5.1.5 .......................................................................................................................... 30 3.6. Simulation 5.1.6 .......................................................................................................................... 34 3.7. Simulation 5.1.7 .......................................................................................................................... 38 3.8. Simulation 5.1.8 .......................................................................................................................... 42 3.9. Simulation 5.1.9 .......................................................................................................................... 46 3.10. Simulation 5.1.10 ........................................................................................................................ 50 3.11. Simualtion 5.1.11 ........................................................................................................................ 54 Simulation 5.4. Figure 3 Configuration ................................................................................................. 58

4. Bungee Compliance Assessment ........................................................................................................ 63

5. Summary and Evaluation .................................................................................................................... 64

6. References .......................................................................................................................................... 71

7. Appendix I. Splicing 12 Strand Single Braid for Moorings ................................................................... 72

5

Table of Figures

Figure 1. DRDC Original SHOL 2C Mooring ................................................................................................. 10 Figure 2. DRDC SHOL 2D New Mooring Design........................................................................................... 11 Figure 3. DRCD SHOL 2D Modified Proposed New Design ......................................................................... 12 Figure 4. Simulation 5.1.1 wave height time series .................................................................................... 14 Figure 5. Simulation 5.1.1 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ....... 16 Figure 6. Simulation 5.1.1 Mooring Profile with Static Currents Conditions .............................................. 17 Figure 7. Simulation 5.1.1 near Surface Mooring Profile with Static Currents Conditions ......................... 17 Figure 8. Simulation 5.1.2 wave height time series .................................................................................... 18 Figure 9. Simulation 5.1.2 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ....... 20 Figure 10. Simulation 5.1.2 Mooring Profile with Static Currents Conditions ............................................ 21 Figure 11. Simulation 5.1.2 near Surface Mooring Profile with Static Currents Conditions ....................... 21 Figure 12. Simulation 5.1.3 wave height time series .................................................................................. 22 Figure 13. Simulation 5.1.3 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ..... 24 Figure 14. Simulation 5.1.3 Mooring Profile with Static Currents Conditions ............................................ 25 Figure 15. Simulation 5.1.3 near Surface Mooring Profile with Static Currents Conditions ....................... 25 Figure 16. Simulation 5.1.4 wave height time series .................................................................................. 26 Figure 17. Simulation 5.1.4 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ..... 28 Figure 18. Simulation 5.1.4 Mooring Profile with Static Currents Conditions ............................................ 29 Figure 19. Simulation 5.1.4 near Surface Mooring Profile with Static Currents Conditions ....................... 29 Figure 20. Simulation 5.1.5 wave height time series .................................................................................. 30 Figure 21. Simulation 5.1.5 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ..... 31 Figure 22. Simulation 5.1.5 Mooring Profile with Static Currents Conditions ............................................ 32 Figure 23. Simulation 5.1.5 near Surface Mooring Profile with Static Currents Conditions ....................... 33 Figure 24. Simulation 5.1.6 wave height time series .................................................................................. 34 Figure 25. Simulation 5.1.6 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ..... 36 Figure 26. Simulation 5.1.6 Mooring Profile with Static Currents Conditions ............................................ 37 Figure 27. Simulation 5.1.6 near Surface Mooring Profile with Static Currents Conditions ....................... 37 Figure 28. Simulation 5.1.7 wave height time series .................................................................................. 38 Figure 29. Simulation 5.1.7 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ..... 40 Figure 30. Simulation 5.1.7 Mooring Profile with Static Currents Conditions ............................................ 40 Figure 31. Simulation 5.1.7 near Surface Mooring Profile with Static Currents Conditions ....................... 41 Figure 32. Simulation 5.1.8 wave height time series .................................................................................. 42 Figure 33. Simulation 5.1.8 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ..... 44 Figure 34. Simulation 5.1.8 Mooring Profile with Static Currents Conditions ............................................ 44 Figure 35. Simulation 5.1.8 near Surface Mooring Profile with Static Currents Conditions ....................... 45 Figure 36. Simulation 5.1.9 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ..... 48 Figure 37. Simulation 5.1.9 Mooring Profile with Static Currents Conditions ............................................ 48 Figure 38. Simulation 5.1.9 near Surface Mooring Profile with Static Currents Conditions ....................... 49 Figure 39. Simulation 5.1.10 wave height time series ................................................................................ 50

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Figure 40. Simulation 5.1.10 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ... 52 Figure 41. Simulation 5.1.10 Mooring Profile with Static Currents Conditions .......................................... 52 Figure 42. Simulation 5.1.10 near Surface Mooring Profile with Static Currents Conditions..................... 53 Figure 43. Simulation 5.1.11 wave height time series ................................................................................ 54 Figure 44. Simulation 5.1.11 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ... 56 Figure 45. Simulation 5.1.11 Mooring Profile with Static Currents Conditions .......................................... 56 Figure 46. Simulation 5.1.11 near Surface Mooring Profile with Static Currents Conditions..................... 57 Figure 47. Simulation 5.4 wave height time series ..................................................................................... 58 Figure 48. Simulation 5.4 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor ........ 60 Figure 49. Simulation 5.4 Mooring Profile with Static Currents Conditions ............................................... 61 Figure 50. Simulation 5.4 near Surface Mooring Profile with Static Currents Conditions .......................... 61 Figure 51. Comparison of Maximum Dynamic Tensions ............................................................................ 67 Figure 52. Comparison of Triaxys Buoy Reserve Buoyancy after Maximum Dynamic Tension .................. 67 Figure 53. Comparison of Average Dynamic Tension ................................................................................. 68 Figure 54. Comparison of Reserve Buoyance after Average Dynamic Tension .......................................... 68 Figure 55. Comparison of Static Tensions. Currents only. .......................................................................... 69 Figure 56. Comparison of Triaxys Buoy Reserve Buoyancy after Static Tension. Currents only. ............... 69 Figure 57. Comparison Dynamic Tension at Anchor ................................................................................... 70 Figure 58. Comparison of Average Dynamic Tension at Anchor ................................................................ 70

Table of Tables

Table 1. Ocean Current Profile used in Simulations ..................................................................................... 8 Table 2. List of Planned Simulations ............................................................................................................. 9 Table 3. Simulation 5.1.1 Environmental conditions .................................................................................. 14 Table 4. Simulation 5.1.1 Buoy and Anchor Tension Results ...................................................................... 15 Table 5. Simulation 5.1.2 Environmental conditions .................................................................................. 18 Table 6. Simulation 5.1.2 Buoy and Anchor Tension Results ...................................................................... 19 Table 7. Simulation 5.1.2 Environmental conditions .................................................................................. 22 Table 8. Simulation 5.1.3 Buoy and Anchor Tension Results ...................................................................... 23 Table 9.Simulation 5.1.4 Environmental conditions ................................................................................... 26 Table 10. Simulation 5.1.4 Buoy and Anchor Tension Results .................................................................... 27 Table 11. Simulation 5.1.5 Environmental conditions ................................................................................ 30 Table 12. Simulation 5.1.5 Buoy and Anchor Tension Results .................................................................... 31 Table 13. Simulation 5.1.6 Environmental conditions ................................................................................ 34 Table 14. Simulation 5.1.6 Buoy and Anchor Tension Results .................................................................... 35 Table 15. Simulation 5.1.7 Environmental conditions ................................................................................ 38 Table 16. Simulation 5.1.7 Buoy and Anchor Tension Results .................................................................... 39 Table 17. Simulation 5.1.8 Environmental conditions ................................................................................ 42 Table 18. Simulation 5.1.8 Buoy and Anchor Tension Results .................................................................... 43 Table 19. Simulation 5.1.9 Environmental conditions ................................................................................ 46 Table 20. Simulation 5.1.9 wave height time series ................................................................................... 46

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Table 21. Simulation 5.1.9 Buoy and Anchor Tension Results .................................................................... 47 Table 22. Simulation 5.1.10 Environmental conditions .............................................................................. 50 Table 23. Simulation 5.1.10 Buoy and Anchor Tension Results .................................................................. 51 Table 24. Simulation 5.1.11 Environmental condtions ............................................................................... 54 Table 25. Simulation 5.1.11 Buoy and Anchor Tension Results .................................................................. 55 Table 26. Simulation 5.4 Environmental conditions ................................................................................... 58 Table 27. Simulation 5.4 Buoy and Anchor Tension Results ....................................................................... 59

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1. Mooring Simulation Tasks

Sea State Conditions to Simulate: Ocean Depth: 122 metres Significant Wave Height (Hs): 12 metres Peak Wave Period (Tp): 15 seconds Ocean Currents: 0.58 metres per second at surface to 0.29 metres per second at ocean bottom. Derived from given currents in Statement of Work (Reference 1): with a Depth Averaged current [U(m)] of 0.5 m/s using Power Law for profile: U(z) = U(m) (Z/0.32*d)^(1/7) Where: Z is the height above seabed d is the water depth U(z) is the current velocity at height(z) U(m) is the depth averaged current velocity Table 1. Ocean Current Profile used in Simulations

Simulation Velocity Profile Depth(m) Velocity(m/s)

0 0.58 7 0.58

12 0.58 22 0.57 42 0.55

121 0.29

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Table 2. List of Planned Simulations

5.1.1 Original as per figure 1 (December 2015 deployment) 5.1.2 Substitute all ¾” diameter 3-strand poly rope with 7/16” diameter Amsteel-blue

Rope in figure 1. 5.1.3 Change 135 m of 3/4” poly to 450 m of 1” poly (4:1 ratio) figure 1. 5.1.4 Change 135 m of ¾” poly to 450 m of 7/16” Amsteel-Blue (4:1 ratio) figure 1. 5.1.5 Figure 2 configuration (2:1 ratio + chain). 220m (205+15) Amsteel blue with 2 Vinycon

buoys 5.1.6 Figure 2 configuration; substitute 7/16” Amsteel-Blue with 1” 3-strand poly (2:1

Ratio + chain). 5.1.7 Figure 2 configuration; change 205 m 7/16” Amsteel-Blue to 327 m of 7/16”

Amsteel- Blue (3:1 ratio + chain). 5.1.8 Figure 2 configuration; change 205 m 7/16” Amsteel-Blue to 327 m of 1” 3-

Strand poly (3:1 ratio + chain). 5.1.9 Figure 3 configuration; 220 m 3/8” (9mm) Amsteel Blue + 6m Vectran rope with 3

Vinycon buoys 5.1.10 Figure 3 configuration; 220m 3/8” (10mm) XTrema Line + 6m Vectran rope with 3

Vinycon Buoys. 5.1.11 Figure 3 configuration; 220m 7/16” (11mm) Amsteel Blue Line + 6m Vectran rope with 3

Vinycon Buoys. 5.4 Extreme Simulation of optimum mooring with HS: 18m and Tp: 20s.

Figure 2 configuration (2:1 ratio + chain).

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Figure 1. DRDC Original SHOL 2C Mooring

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Figure 2. DRDC SHOL 2D New Mooring Design

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Figure 3. DRCD SHOL 2D Modified Proposed New Design

13

2. WHOI CABLE Program The WHOI Cable version 2.0 program was used for the mooring simulations. (Reference 2 ). Axys Technologies, Inc. has been using the WHOI Cable program since 2006 to design and test many oceanographic moorings and has not found any problems with deployments that range worldwide. The WHOI Cable program, itself, was designed specifically for Oceanographic mooring systems and tested by the Woods Hole Oceanographic Institution. The solutions were a 2 Dimensional dynamic simulation with input currents and waves propagation in the same direction. A static simulation is resolved at the same time based on input currents. The mean and maximum dynamic, including static tensions at the Buoy and Anchor are presented. Environment input conditions are presented as well as an analysis of output wave heights. The output wave height statistics are determined from the buoy heave in the simulation. For the simulation the following wave statistics are presented: Significant Wave Height (Hs) is estimated from 4 times the Standard Deviation of the wave height time series. Tz is the zero crossing period which is determined from the number of zero crossings divide the time length in seconds of the wave height time series analysed. Ts is the significant period as calculated from the 1.33 times Tz. Hmax is the maximum wave height as determined from manually picking the largest trough to peak waves in the simulation wave height time series graph.

14

3. Simulations 3.1. Simulation 5.1.1

Table 3. Simulation 5.1.1 Environmental conditions

Figure 4. Simulation 5.1.1 wave height time series

Parameter Input

Hs: 12

Tp : 15

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 12.1

Hmax : 16.3

Ts : 13.8

Tz : 10.3

Simulation 5.1.1 Environmental Conditions

-10-8-6-4-202468

10

200 250 300 350 400 450 500

Heig

ht (m

)

Time (s)

Simulation 5.1.1: Wave Height Time Series

15

Table 4. Simulation 5.1.1 Buoy and Anchor Tension Results

lbs Kg

Maximum DynamicTension at Buoy 539 244

Average Dynamic Tension at Buoy 172 78

Reserve Buoyancy after Maximum Dynamic Tension -27 -12

Reserve Buoyancy after Average Dynamic Tension 339 154

Maximimum Dynamic Tension at Anchor 520 236

Average Dynamic Tension at Anchor 167 76

Static Tension at Buoy 89 40

Reserve Buoyancy after Static Tension at Buoy 422 192

Reserve Buoyancy of TRIAXYS Buoy 511 232

Dynamic Analysis

Static Analysis

Simulation 5.1.1

16

Figure 5. Simulation 5.1.1 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor

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Dynamic Simulation 5.1.1for Depth: 122m

Waves: Hs=12.0 m Tp=15s Currents: 0.58 m/s Surface to 0.29 m/s BottomTriaxys NW Total Reserve Buoyancy: 511 lbs

Reserve after Maximum Dynamic Tension: -27 lbsReserve after Mean Dynamic Tension: 339 lbs

Tension at Anchor (lbs) Tension at Buoy (lbs) Reserve Buoyancy

17

Figure 6. Simulation 5.1.1 Mooring Profile with Static Currents Conditions

Figure 7. Simulation 5.1.1 near Surface Mooring Profile with Static Currents Conditions

0

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0 10 20 30 40 50 60 70 80 90 100 110 120

Simulation 5.1.1Static Mooring Analysis for Depth: 122m

Currents: 0.58m/s Surface to 0.29m/s BottomTriaxysNW Total Reserve Buoyancy: 511 lbs

Tension at Buoy: 89 lbsTension at Anchor: 82 lbs

110

115

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125

105 110 115 120 125




18

3.2. Simulation 5.1.2



Parameter Input

Hs: 12

Tp : 15

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 13.3

Hmax : 16.3

Ts : 17.3

Tz : 13.0


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Heig

ht (m

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Time (s)


19


lbs Kg



Reserve Buoyancy after Maximum Dynamic Tension -103 -47







Dynamic Analysis

Static Analysis

Simulation 5.1.2

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Reserve after Maximum Dynamic Tension: -103 lbsReserve after Mean Dynamic Tension: 353 lbs


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Simulaton 5.1.2Static Mooring Analysis for Depth: 122m



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3.3. Simulation 5.1.3 Table 7. Simulation 5.1.2 Environmental conditions


Parameter Input

Hs: 12

Tp : 15

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 9.7

Hmax : 12.7

Ts : 16.6

Tz : 12.5


-10-8-6-4-202468

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Heig

ht (m

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Time (s)


23


lbs Kg



Reserve Buoyancy after Maximum Dynamic Tension 233 106







Dynamic Analysis

Static Analysis

Simulation 5.1.3

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Reserve after Maximum Dynamic Tension: 233 lbsReserve after Mean Dynamic Tension: 462 lbs


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3.4. Simulation 5.1.4 Table 9.Simulation 5.1.4 Environmental conditions


Parameter Input

Hs: 12

Tp : 15

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 9.7

Hmax : 12.3

Ts : 15.3

Tz : 11.5


-10-8-6-4-202468

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ht (m

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Time (s)


27


lbs Kg










Dynamic Analysis

Static Analysis

Simulation 5.1.4

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Parameter Input

Hs: 12

Tp : 15

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 12.2

Hmax : 16.8

Ts : 14.3

Tz : 10.7

Simulation Environmental Conditions

Simulation 5.1.5

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lbs Kg










Dynamic Analysis

Static Analysis

Simulation 5.1.5

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Parameter Input

Hs: 12

Tp : 15

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 13.1

Hmax : 12.9

Ts : 16.6

Tz : 12.5


Simulation 5.1.6

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lbs Kg










Dynamic Analysis

Static Analysis

Simulation 5.1.6

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Parameter Input

Hs: 12

Tp : 15

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 14.2

Hmax : 14.1

Ts : 19.0

Tz : 14.3


Simulation 5.1.7

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lbs Kg










Dynamic Analysis

Static Analysis

Simulation 5.1.7

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Parameter Input

Hs: 12

Tp : 15

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 15.7

Hmax : 13.3

Ts : 20.0

Tz : 15.0


Simulation 5.1.8

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ht (m

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lbs Kg










Dynamic Analysis

Static Analysis

Simulation 5.1.8

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0102030405060708090

100110120130

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400

Simualtion 5.1.8Static Mooring Analysis for Depth: 122m



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Table 20. Simulation 5.1.9 wave height time series

Parameter Input

Hs: 12

Tp : 15

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 11.7

Hmax : 16.0

Ts : 12.5

Tz : 9.4


Simulation 5.1.9

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ht (m

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Time (s)


47


lbs Kg










Dynamic Analysis

Static Analysis

Simulation 5.1.9

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50




Parameter Input

Hs: 12

Tp : 15

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 11.8

Hmax : 15.9

Ts : 13.8

Tz : 10.3


Simulation 5.1.10

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ht (m

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Time (s)


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lbs Kg










Dynamic Analysis

Static Analysis

Simulation 5.1.10

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3.11. Simualtion 5.1.11

Table 24. Simulation 5.1.11 Environmental condtions


Parameter Input

Hs: 12

Tp : 15

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 11.7

Hmax : 15.8

Ts : 12.5

Tz : 9.4


Simulation 5.1.11

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Heig

ht (m

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Time (s)


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lbs Kg










Dynamic Analysis

Static Analysis

Simulation 5.1.11

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58

Simulation 5.4. Figure 3 Configuration Table 26. Simulation 5.4 Environmental conditions

Figure 47. Simulation 5.4 wave height time series

Parameter Input

Hs: 18

Tp : 20

Cv -surface : 0.58

Cv- mid : 0.53

Cv -bottom : 0.29

Simulation

Hs : 18.4

Hmax : 20.9

Ts : 20.0

Tz : 15.0


Simulation 5.4

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Heig

ht (m

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Time (s)

Simulation 5.4: Wave Height Time Series

59

Table 27. Simulation 5.4 Buoy and Anchor Tension Results

lbs Kg










Dynamic Analysis

Static Analysis

Simulation 5.4

60

Figure 48. Simulation 5.4 Dynamic Mooring Analysis Time Series of Tensions on Buoy and Anchor

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Time (s)

Dynamic Simulation 5.4for Depth: 122m




61

Figure 49. Simulation 5.4 Mooring Profile with Static Currents Conditions

Figure 50. Simulation 5.4 near Surface Mooring Profile with Static Currents Conditions

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4. Bungee Compliance Assessment The Standard Compliant Sections provided by AXYS Technologies Inc. for the TRIAXYS™ Directional Wave Buoy have a Termination Pull out between 1000 and 1200 pounds. In order to facilitate operational mooring tensions of 2500 lbs a Special Build of the Axys Compliant section which limits the extent such that tensions on the compliant sections terminations are no more than 250 lbs were constructed. The Samson Ropes Amsteel™ Safety Line is a shortened length to enable this. Excess tension will be taken up by the Safety Line which has a Minimum Breaking Strength of 16,200 lbs. This is a Safety Factor of 6.6 on the maximum expected operational tension of 2500 lbs.

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5. Summary and Evaluation With the given environmental conditions the 2 variations of the original SHOL 2C, the dynamic tensions were the highest of the simulations tested. Both the SHOL 2C with Polypropylene and Amsteel™ (Dyneema™) rope resulted in the dynamic tensions being higher than the reserve buoyancy. This simulations indicates that the Triaxys Buoy would have been submerged momentarily with these moorings and environmental conditions. The SHOL 2C with Amsteel™ variation showed higher maximum dynamic tension, but lower average dynamic and static tension. This due to the characteric of the Polypropylene line being more elastic under tension than the Amsteel™ Dyneema™ therefore under dynamic tension the elasticity allows the Polypropylene to stretch more and momentarily relieve some of the tension. However, under static and average dynamic tension the larger diameter of the Polypropylene rope creates more drag on the mooring with the given result being higher average dynamic and static tensions. The results of a longer mooring and therefore larger scope result in lowering dynamic tensions, however the long scope on positively buoyant rope will likely become operationally problematic in lighter environmental conditions because of the hazard of the rope floating to the surface or near surface. The use of 3 strand polypropylene is not recommended for large scope moorings in the deep sea. This is because under cyclic tensions the 3 strand rope after a large tension will start to hockle then twist on itself. This results in an overall shortening of the mooring and creates tangled points which are points of buoyancy which in turn results in more tangling and shortening of the mooring. (Reference 3). If polypropylene rope is to be used it should be a torque balanced braid such as 8 strand plaited or a 12 strand single braid. For slack line and inverse catenary style moorings, Double Braid rope should also be avoid because under cyclic tension with high loading the outer cover will creep into bunches and create high tensions on the inner core between these bunches. The high tensions on the core will eventual fatigue the fiber and lead to breakage. The new proposed SHOL 2D mooring simulations with 220 meters (205m+15m) of Amsteel™ rope performed much better than the original SHOL 2C moorings with 150m of Polypropylene and Double braid rope. The reason being partly that the SHOL 2D mooring with a smaller diameter Amsteel™ does result in less drag force, but to a large part the longer mooring helps to relieve the overall tension of the mooring. The simulations with the 327m longer rope resulted in higher maximum dynamic tensions but lower average dynamic tension and static tension. This likely due to the longer rope having an overall better elasticity and also possibly due to dynamic motion drag due to the longer rope damping the maximum tensions. Under average and static conditions the longer rope has more drag and which will therefore result in higher average dynamic and static tensions.

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The newest SHOL 2D (Figure 3) mooring design using 3 Vinycon subsurface floats, 220 m of 10 mm XTrema ™ (Dyneema™) rope with 6 m of 12mm Vectran™ rope performs the best. Variations on this design were also done using 9mm and 11mm Amsteel™ rope which resulted in showing small variances on the tenstions. It can be conclude the main factors in the better performance were likely due to the addition of the additional subsurface buoyancy and the use of the negatively buoyant Vectran rope near the surface.

Recommendations:

The newest mooring design (Figure 3) appears to have very good performance in comparison to the other moorings simulated. Some minor changes that we would recommend are:

1. Splicing of rope eyes should be done with the Herzog style eye splice. This eye splice locks the splice and prevents pullout that can occur in cycling tensions. See Appendix I. Splicing 12 Strand Single Braid for Moorings. For Supplementary Instructions see the following online videos:

12-Strand Single Braid Eye Splice for Moorings: https://vimeo.com/43442821 12-Strand Single Braid End for End Splice for Moorings: https://vimeo.com/97493078

Another suitable 12 strand eye splice is the Brummel-Lock Eye Splice.

See: http://www.phillystran.com/Resource_/PageResource/Phillystran%20Brummel-Lock%20Splice%20Procedure.pdf

2. For the Vectran to XTrema Line connection we would recommend either the Herzog End for End

Splice or that the 2 ropes be joined with a Strop Bend (Cow Hitch) instead of having an Hard Eye and Shackle. The End for End splice will have 90% efficiency in strength and the Strop Bend will have 85 to 90% efficiency of Splice. (Reference 4 and 5). The Strop Bend (Cow Hitch) has the advantage of being easily replacing rope sections during service. It also, removes the possibility of metallic corrosion and wear at these connections. See Figure 51

https://vimeo.com/43442821


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Figure 51. Making a Strop Bend (Cow Hitch) on 2 ropes with Eye Splices

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Following are graphs comparing the Simulations:

Figure 52. Comparison of Maximum Dynamic Tensions

Figure 53. Comparison of Triaxys Buoy Reserve Buoyancy after Maximum Dynamic Tension

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Figure 54. Comparison of Average Dynamic Tension

Figure 55. Comparison of Reserve Buoyance after Average Dynamic Tension

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Figure 56. Comparison of Static Tensions. Currents only.

Figure 57. Comparison of Triaxys Buoy Reserve Buoyancy after Static Tension. Currents only.

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Figure 58. Comparison Dynamic Tension at Anchor

Figure 59. Comparison of Average Dynamic Tension at Anchor

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6. References

1. DRDC-ARC Statement of Work. 2016. PReq 2016-07644 2. Gobat, Jason, M. Grosenbaugh, and M.S. Triantafyllou, 1997. WHOI Cable:

Time Domain Numerical Simulation of Moored and Towed Oceanographic Systems. Technical Report WHO-97-15. Woods Hole Oceanographic Institution. Woods Hole, MA 02543

3. Paul Gates, Peter Cusack and Peter Watt. 1996. SOUTH PACIFIC COMMISSION

FISH AGGREGATING DEVICE (FAD) MANUAL. VOLUME II RIGGING DEEP-WATER FAD MOORINGS. South Pacific Commission Noumea, New Caledonia

4. Samson Rope Inc. 2014. ROPE USER'S MANUAL. Guide to Rope Selection,

Handling, Inspection and Retirement. SamsonRope.com 5. Pederson, Mark, Greg Mozgai and Danielle Stenvers. 2011. The Effect of

Bending on the Tensile Strength of Statically Loaded Synthetic Ropes. 2011 MTS/OIPEEC 9th International Rope Technology Workshop.

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7. Appendix I. Splicing 12 Strand Single Braid for Moorings

For Supplementary Instructions see the following online videos: 12-Strand Single Braid Eye Splice for Moorings: https://vimeo.com/43442821 12-Strand Single Braid End for End Splice for Moorings: https://vimeo.com/97493078

12 Strand Single Braid Splicing Instructions for Oceanographic Moorings

1 Eye Splice

Figure 60. 12 Strand Single Braid locked Eye Splice



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Eye Splice Procedure

1. Measurement: Tape end of line to be spliced and measure one (1) “tubular” fid length (2 wire fid lengths because wire fid is ½ size) from the end of the line and make Mark #1. One tubular fid length is about 22 times the diameter of the rope. From Mark #1 measure another tubular fid length (2 wire fid lengths) then make Mark #2. Now for the size of eye desired and make Mark #3.

Figure 61. Measurement with Fids for splicing

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2. Taper: From Mark #1, in the direction of the taped end of the line, mark every 2nd right and left strands (paralleled pairs of strands) for 3 pairs. ( See insert figures #3 and #4).

Figure 62. From Mark #1, toward taped end. Mark every 2nd Right & Left pair of Strands

Figure 63. Cut each pair of marked strands. Pull out rope from end.

Cut every 2nd pair of marked strands and pull out of line (note: tape may have to be removed in order to pull out strands). Tapered end will now have only 5 pairs of strands remaining. Tape tapered tail tightly to keep from unbraiding during rest of splicing procedure.

Figure 64. The Tapered end.

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3. Locking: Attach fid to tapered end of line. At Mark #3 pass fid completely through line and go between strands. Pull on fid and tapered tail until Mark #2 just disappears inside stranding part of line. Be sure not to twist line.

Figure 65. Pull fid through Mark 1 and pull rope through to align Mark 2 and 3 to form the eye.

Note: With line 1/4” to 5/8” diameter only one lock tuck has to be done, however 3 is recommended for increased security. Lines of 5/8” diameter to 1-5/16” diameter ( 4” circumference, 3 lock tucks should be done. See Step 4 for proper procedure on addtionnal locks. If your particular application will not allow locking proceed with Step 5, burying the tapered tail about 1-1/4 fid lengths starting at Mark 3.

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4. Additional Locking:

Count down four (4) pairs of strands from point where tail comes out standing pair. This is about 1 diameter of the rope. Insert fid through the rope, centered between fourth and fifth pairs of strands (See figure) then pull tail through. Repeat Steps 3 and 4 two more times. Four passes of tail section will have been made through the standing part of the line. Be sure the line has no twists.

Figure 66. Additional Locking

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5. Bury Taper:

Measure about 1-1/4 tubular fid length ( 2-1/2 wire fid lengths), then create a Mark #4. Then count down four (4) pairs of strands from the standing part of the line from the last insertion. Insert the fid and tapered tail at this point, through the hollow of the rope, and bring the fid out at Mark #4. Pull fid and tapered tail out. Don’t let the line twist. Note: if no “locks” are to be used, Insert fid at Mark 3, then work a distance of 1-1/4 fid lengths through hollow of the rope, to bury tapered tail.

Figure 67. Bury Taper. Push fid through to Mark 4 and pull tapered tail through.

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6. Complete Taper: Remove fid. Remove tape from taper. Pull hard on tapered tail with one hand. (See insert 1 and 2). With other hand smooth bunched line away from eye splice. Be sure all tucks are tight and that there is no slack. Now, cut off tail at an angle close to the end of the standing part of line. Smooth cover once more, away from the eye to bury tail. With larger ropes it is easier to bury by tying a small line to eye and securing firmly to fixed object. Then, with both hands and weight of body, smooth cover slack to tighten locks and bury tail in standing part.

Figure 68. Complete Taper. Finished 3 Lock and 1 Lock Splice

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2 Fid Specifications

Table 28. Tubular Fid Specifications

Rope Circumference Rope Diameter Fid Short Section Length

Total Fid Length

3/4" 1/4 “ 2-1/16” 5-1/2” 1” 5/16 ” 2-1/2” 6-3/4”

1-1/8” 3/8 “ 2-7/8” 7-3/4” 1-1/4” 7/16 “ 3-9/16” 9-1/2” 1-1/2” 1/2 “ 4-1/8” 11” 1-3/4” 9/16 “ 3-5/8” 12-1/4”

2” 5/8 “ 4/1/8” 14” 2-1/4” 3/4 “ 4-3/4” 16” 2-3/4” 7/8 “ 4-3/4” 19”

3” 1 “ 5-1/4” 21”

Table 29. Wire Fid Specifications

Rope Circumference Rope Diameter Fid Short Section Length

Total Fid Length (L)

3/4" 1/4 “ 1” 2-3/4” 1” 5/16 ” 1-1/4” 3-3/8”

1-1/8” 3/8 “ 1-1/2” 3-7/8” 1-1/4” 7/16 “ 1-3/4” 4-3/4” 1-1/2” 1/2 “ 2” 5-1/2” 1-3/4” 9/16 “ 1-7/8” 6-1/8”

2” 5/8 “ 2” 7” 2-1/4” 3/4 “ 2” 8” 2-3/4” 7/8 “ 2-3/8” 9-1/2”

3” 1 “ 2-5/8” 10-1/2” 3-3/4” 1-1/4” 3-1/4” 13-1/4” 4-1/2” 1-1/2” 4” 16” 5-1/2” 1-3/4” 4-3/4” 19”

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3 End for End Splice

Figure 69. End for End Splice

TOOLS NEEDED: Electrical Tape, Marking Pen, Scissors, Fid and Tape Measure. Step 1: Lay two ends side by side and Mark #1 at one tubular Fid length (~22 times diameter of rope) from end of ropes. Mark #2 at two tubular fid lengths from end of ropes.

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Step 2: From Mark #1, working toward the end of the rope, mark every 4th pair of strands right and left lay 4 times.

Step 3: Start your taper by pulling out the marked strands. For the last 3 marked pairs, cut and remove every 4th left and right lay back to the end of the rope. If necessary, such as in larger diameter ropes, cut off excess on tail at an angle to give final tapered effect.

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Step 4: Take one end of the tapered rope, with fid attached, and then pass it through Mark 2 of the second rope. Count 3 pairs of strands and pass through again. Repeat a total of 3 times. Insert the tapered section directly through the hollow of the rope and pull until the full section that is tapered is buried in the body of the rope.

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Step 5: Take the end of the other rope and repeat Step 4 above.

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Step 6: Bury the ends and milk back on both ends to remove excess slack on crossover.

wave buoy mooring design evaluation

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