Following the tests, the DP system underwent further fine-tuning. “One of the things we learnt was that there was quite a large differ- ence between the generic, DP controller and the Kongsberg controller. The generic con- troller keeps the vessel in position without a preference for a direction, and as a result the vessel moves in a circular envelope. What we saw with the Kongsberg controller is that it managed to reduce the sideways motions at the expense of the longitudinal motions, making the envelope more elliptical. This results in smaller distance variations to the turbine and thus, makes it easier for the gangway to compensate for the residual motions,” Peter explains.


The full optimisation will be carried out in a follow up project - HIL simulator with DP, Access and Vessel.


Deciding factor Peter stresses: “I think the MARIN tests were the deciding factor for Bibby Marine Services – they really made the difference!” And subsequently, Bibby Marine Services placed an order for the first Damen SOV on January 15 and the ‘Bibby WaveMaster 1’ is now under construction. Leading DP company and supplier to the SOV, Kongsberg was also present.


The results were even better than expected, Peter adds. “They provided the confirmation we needed – that the design was suitable for a certain operational area. MARIN was needed so we could test the design, while taking into account the designated wave height and wave period. In a 2.5 m significant wave height and period of 6-8 seconds, the SOV proved its capabilities, in that it wasn’t rolling at all.


“We wanted to examine the SOV in the environmental conditions, whilst considering the comfort levels. It has to be stable and reduce accelerations as much as possible. We found that heave and roll motions reduce by a substantial 10-15% by optimising the design to the required metocean conditions. And of course, fewer accelerations means that it is much safer onboard.”


Safe sea transfer Crucially, the SOV vastly improves the sea transfer. The SOV deploys a motion-compensated access gangway system mounted on the port side. Its managing software is aligned with the vessel’s DP system to accommodate gang- way motion limits.


8 report


Regarding future work, Damen is keen to investigate integration aspects and whether DP and motion compensation systems (i.e. the gangway) can be integrated to optimise mean, low frequent and wave frequent motion compensation. And MARIN’s aNySIM simulations will help here. Peter comments: “Regarding integration for the current design Damen is using the existing solution that our suppliers offer but in the future we indeed want to investigate what the increase in total system performance is when all the available information is integrated in the control of both the access system, power management and DP control system. Opera- tionally, an integrated solution might be beneficial because the crew of the vessel is than capable of indicating more accurately if an operation can be carried out safely.”


Turbine-vessel model Meanwhile, a turbine-vessel interaction model has also been developed by Damen and MARIN. Peter explains: “Over the last few years a lot of research effort has been invested in under- standing the classical Crew Transfer Vessel operations (Bump-and-Jump) to be able to improve the operability of the Damen FCS2610 and possible new designs for the offshore wind industry.”


A key part of the operational success is determined by the quality of the fender and this is defined by the durability, shock absorption characteristics and the capability to predictably transfer vertical loads, he says. “This turned out to be a set of require- ments that was not so easy to find within our supplier base. To be able to properly specify what the exact characteristics need to be for a new fender design Damen built up detailed knowledge on the exact physics during the landing phase. As a part of this we jointly developed an interaction model to be able to assess the influence of the fender characteristics on the vessel’s behaviour while moored against an offshore boat landing.


As Report went to press, MARIN was also set to deliver a full computer simulation model, including DP to Damen, which would be a real-life, detailed set up of the SOV. “This will be ideal for training the Bibby crews and potential customers in the future,” Peter emphasises.


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