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Crew Transfer Vessel (CTV)
Performance Benchmarking
Presented by
Stephen Phillips of
Seaspeed Marine Consulting Ltd
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BACKGROUND
- CT OWA : The Carbon Trust ‘Offshore Wind Accelerator’ (OWA) brings
together nine offshore wind energy developers to work towards reducing the
cost of renewable energy.
- R&D : One area of their research is into reducing the cost of windfarm access
– novel vessels, transfer devices – and benchmarking of CTV Performance.
- DEVELOPERS : For the Developers, this benchmarking process has enabled
an improved assessment of the benefits of new designs, improved O&M
modelling and improved CTV contracting arrangements (ability to specify and
deploy more suitable vessels for each specific site – and to assure the
achieved performance).
- DESIGNERS : For Designers/Builders/Owners/Operators of CTVs, they are
now able to demonstrate performance benefits using the benchmark as a
basis.
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BENCHMARKING
RESEARCH PROGRAMME
- MARKET STUDY : Market assessment to establish the make-up of the CTV
sector.
- STANDARDS : Development of standardised sea trial procedures for
investigating Transit, Approach and Transfer performance.
- SEA TRIALS : Undertaking of sea trials on a range of vessels to establish
actual performance. Investigate typical limiting parameters (vertical and lateral
accelerations, roll, fender slip etc)
- BASELINE HULL STUDIES : Development of baseline hull forms and
undertaking of computer simulations and scale model tests to better
understand vessel performance and limitations.
- R&D FINDINGS : Presentation of results in the form of Performance Plots –
and a summary of findings from the research.
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MARKET ASSESSMENT
- Market study undertaken in 2015
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SEA STATISTICS
Reference : HSE OTC 2001/030 Report ‘Wind and wave frequency distributions
for sites around the British Isles’
Typical UK Sea Statistics
Sea Area Category
Limited Fetch
(short period on P-Plots)
Exposed
(standard period on P-Plots)
Ocean
(long period on P-Plots)
Hsig,
m
% Exceed’nc
Average
Modal
Period
To, sec
Spread of
Modal
Period
To, sec
% Exceed’nc
Average
Modal
Period
To, sec
Spread of
Modal
Period
To, sec
% Exceed’nc
Average
Modal
Period
To, sec
Spread of
Modal Period
To, sec
0.5 86 4.5 3.5 – 5.5 97 5.0 3.5 – 6.5 98 6.5 4.5 – 8.5
1.0 53 5.0 4.0 – 6.0 80 5.5 4.0 – 7.0 86 7.0 5.0 – 9.0
1.5 31 5.5 4.5 – 6.5 59 6.0 4.5 – 7.5 67 7.5 5.5 – 9.5
2.0 17 6.0 5.0 – 7.0 42 6.5 5.0 – 8.0 51 8.0 6.0 – 10.0
2.5 9 6.5 5.5 – 7.5 30 7.0 5.5 – 8.5 39 8.5 6.5 – 10.5
3.0 5 7.0 6.0 – 8.0 21 7.5 6.0 – 9.0 29 9.0 7.0 – 11.0
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SEA TRIAL AND
ANALYSIS PROCEDURES
- DNV GL / Seaspeed study resulted in document ‘Conduct of offshore access
performance evaluation trials’, OWA-S2-A-Y2-1 October 2015
- Simple tests : For Transit, run at a range of speeds and headings,
measuring/recording triaxial accelerations, pitch and roll, significant wave
height and wave period – and for Transfer, also fender slip and/or loss-of-
contact frequency – along with other environmental and vessel conditions.
- Analyse data: rms, mean, max & min values
- Analyse wave conditions: Hsig, Hmax, Tz
- Record any other adverse conditions
such as tidal current, swell, shallow water etc
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SEA TRIALS
- Transit
- Transfer
- Approach / loiter
- Short / long term
monitoring
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SIMULATION
- Development of baseline hulls and computer simulation
- Scale model simulation
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ACCEPTABILITY
THRESHOLD PARAMETERS
CTV Performance Acceptability Criteria
Transit Acceleration and Motion Limits
Vertical acceleration, rms 1.5 m/s2 (approx. 0.15 g)
Lateral acceleration, rms 1.0 m/s2 (approx. 0.1 g)
Pitch, rms 5 deg
Roll, rms 6 deg
Transfer Motion Limits
Friction limit 95% waves pass with no slip above 300mm (or one ladder rung)
Roll limit, rms 3 deg
Freeboard limit 95% of waves below the average* freeboard
Note * average freeboard is the average of the wet-deck freeboard and the bow freeboard. This parameter is used for computer assessments of
performance and is not expected to be used on sea trials assessments.
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TRANSIT P-PLOT22m CatamaranHsig = 2.0 metres
Head Sea
Beam Sea
Stern Sea
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TRANSFER P-PLOT22m Catamaran
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P-PLOTS WITH SEA TRIALS
RESULTS 26m Catamaran
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BENCHMARK P-PLOTS
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BENCHMARK P-PLOTS
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RESEARCH PROJECT
SUMMARY
Results now available
for public comment
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SEMINAR SUMMARY
Practical Application of P-Plots
• No versatile means of comparing vessel performance was previously
available
• P-plots allow a vessel of any configuration to be compared to an industry
benchmark (with respect to Transit and Transfer)
• Developers have a better understanding of what performance can be
expected from CTVs, more realistic performance data for O&M modelling and
have a basis for the performance assessment of new vessel proposals
• The results of long term performance monitoring can be presented in a simple
format and compared to a known benchmark
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RESEARCH FINDINGS
Effects on Performance of :
- Vessel Type
- Vessel Size
- Bollard Thrust
- Freeboard
- Speed
- Sea State
- Heading
- Shallow Water
- Tidal Current
- Docking Pole Inclination
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RESEARCH FINDINGS
Effect on Performance of :
VESSEL TYPE
Figure A.1 - Transit P-Plots for 22 metre Monohull, Catamaran and Swath
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RESEARCH FINDINGS
Effects on Performance of : VESSEL SIZE
18 metre CTV 22 metre CTV 26 metre CTV
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RESEARCH FINDINGS
Effects on Performance of : VESSEL SIZE
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RESEARCH FINDINGS
Effects on Performance of : BOLLARD THRUST
Figure A.3 - Transfer P-Plot for 22m catamaran showing effect of bollard thrust
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RESEARCH FINDINGS
Effects on Performance of : FREEBOARD
Figure A.4 - Transfer P-Plot for 22m catamaran showing effect of freeboard
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RESEARCH FINDINGS
Effects on Performance of : SPEED
Figure A.5 – Vertical acceleration rms of 22m monohull showing effect of
speed
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RESEARCH FINDINGS
Effects on Performance of : SEA-STATE AND HEADING
Figure A.6 – Vert. acceleration rms of 22m monohull showing effect of Hsig
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RESEARCH FINDINGS
Effects on Performance of :
SHALLOW WATER : Generally steeper waves and thus greater pitch,
roll motions and accelerations. More likely to
encounter confused seas
TIDAL CURRENT : For transfer this can reduce the operational window
and can make approach far more difficult, depending
on relative headings
DOCKING POLE : This was studied during the model tests, with
INCLINATION inclinations up to 7 degrees from the vertical. No
appreciable difference in operational performance
was seen.
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RESEARCH FINDINGS
Effect of Propulsion Arrangement
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RESEARCH FINDINGS
Effect of Access Devices
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CTV PERFORMANCE
BENCHMARKING
Thank you for your attention
Questions?
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DEFINITIONS
Environmental Condition Assessment
- Wave height; Hmax, Hsig
- Wave period; Zero up crossing period, Tz, modal, To and crest period, Tc
- Other important parameters - wind speed and direction, water depth, tidal
current speed and direction, spreading of wave energy
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TRANSIT P-PLOTS22m Catamaran