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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