Post on 06-Mar-2018
transcript
Crew Transfer Vessel (CTV)
Performance Benchmarking
Presented by
Stephen Phillips of
Seaspeed Marine Consulting Ltd
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.
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.
MARKET ASSESSMENT
- Market study undertaken in 2015
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
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
SEA TRIALS
- Transit
- Transfer
- Approach / loiter
- Short / long term
monitoring
SIMULATION
- Development of baseline hulls and computer simulation
- Scale model simulation
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.
TRANSIT P-PLOT22m CatamaranHsig = 2.0 metres
Head Sea
Beam Sea
Stern Sea
TRANSFER P-PLOT22m Catamaran
P-PLOTS WITH SEA TRIALS
RESULTS 26m Catamaran
BENCHMARK P-PLOTS
BENCHMARK P-PLOTS
RESEARCH PROJECT
SUMMARY
Results now available
for public comment
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
RESEARCH FINDINGS
Effects on Performance of :
- Vessel Type
- Vessel Size
- Bollard Thrust
- Freeboard
- Speed
- Sea State
- Heading
- Shallow Water
- Tidal Current
- Docking Pole Inclination
RESEARCH FINDINGS
Effect on Performance of :
VESSEL TYPE
Figure A.1 - Transit P-Plots for 22 metre Monohull, Catamaran and Swath
RESEARCH FINDINGS
Effects on Performance of : VESSEL SIZE
18 metre CTV 22 metre CTV 26 metre CTV
RESEARCH FINDINGS
Effects on Performance of : VESSEL SIZE
RESEARCH FINDINGS
Effects on Performance of : BOLLARD THRUST
Figure A.3 - Transfer P-Plot for 22m catamaran showing effect of bollard thrust
RESEARCH FINDINGS
Effects on Performance of : FREEBOARD
Figure A.4 - Transfer P-Plot for 22m catamaran showing effect of freeboard
RESEARCH FINDINGS
Effects on Performance of : SPEED
Figure A.5 – Vertical acceleration rms of 22m monohull showing effect of
speed
RESEARCH FINDINGS
Effects on Performance of : SEA-STATE AND HEADING
Figure A.6 – Vert. acceleration rms of 22m monohull showing effect of Hsig
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.
RESEARCH FINDINGS
Effect of Propulsion Arrangement
RESEARCH FINDINGS
Effect of Access Devices
CTV PERFORMANCE
BENCHMARKING
Thank you for your attention
Questions?
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
TRANSIT P-PLOTS22m Catamaran