WTIVS: The future – New generation designs

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Before any wind turbines are installed, before any installation vessels are built and before any orders have been placed to build the vessels the statistics show that one company in this industry continues to have more influence in this sector than the rest of the sector all together. GustoMSC has designed part of the vast majority of the wind turbine installation vessels working or on order today. With such an influence on current vessels who better is able to influence the vessels of the future?

Of the 16 new installation vessels currently working in the offshore wind sector most of them are self elevating vessels or as some prefer to call them self propelled jack ups. Market research analysts indicate that there may be as many as twice this number, or as few as ten new builds required in the future but certainly there will be many more vessels required to meet the installation needs in the future.

So what will these vessels be needing to cater for deeper water; larger turbines and different foundations? Offshore WIND asked Jan Mark Meeuwisse, Sales Manager Jack-ups, and Andries Hofman, Senior Project Manager Jack-ups, from GustoMSC to give their opinions.

After asking their future clients what it is that they will need to look at carefully in the future they have come to one conclusion. With one voice they stated 'logistics', and the need to avoid bottlenecks. There is no difficulty making or installing the units, the major difficulties are to be found in the whole logistics chain which needs to be a well oiled machine. Just one breakdown in this chain will cause delays or even stop the whole process. The parameters for new designs must result in a means to lift heavy and delicate components, at sea, to great heights, repetitively.

However not all of these vessels will be jack ups. The components making up the bigger wind farms will result in diversification of vessels in the chain where conventional, but specifically designed, flat decked floating vessels can be used for installing the foundations, and jack ups for the WTG and blades.

The utilization of feeders, pontoons or flat decked vessels, to keep the crane offshore working for longer periods, would be perfect but this will prove to be very difficult with the transferring of the nacelle and blade components at sea.

However, the less delicate foundations could well utilise a feeder programme. Transit time sailing in and out of port will prove to be a more efficient use of time than waiting for weather conditions to allow transfers at sea. Here the risk factor of component damage would be too great.

As if to complicate this view, or just to provide an alternative, the two prognosticators then throw another idea into the frame; a self elevating feeder vessel without a heavy lift crane - just deck space - which would allow a stable platform for the safe transfer at sea of these delicate components. A simple design project for GustoMSC, no doubt.

Keep it simple!

Whatever vessel is used for the conveyance of these components it will be essential to keep the chain simple, allowing for the control of the sea fastenings and the process, by surveyors for regulatory, safety and insurance purposes, to be fast, easy and efficient on the WTIV. The design of the deck area will have to allow for this.

WTIV's built for water depths of 45m can be built for US$ 160m. To make them big enough to be able to work in water as deep as 65 -70m pushes up the price to more than US$ 250m.

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These vessels with this capability are being designed with a second market in mind, oil & gas support and decommissioning projects that will provide alternative employment in the future.

They are bigger in every dimension. The cranes are bigger, the legs are stronger and take up more space, and therefore the deck area has to be increased to keep it useful.

Using a rule of thumb calculation, dividing the build price by 1000 gives an indication of the day rate. Day rates for self-propelled installation vessels are expected to range between $60,000 and $300,000 per day in the period from now to 2017.

For the offshore wind sector though they envisage that most of the wind farms will be built in waters not deeper than 45m.

Challenging factors

There are, however, more factors involved in the calculations. The vessel will have to be able to withstand storms, and allow for differing leg penetration in the various types of sea beds encountered. An air-gap of 7.5m is acceptable for perfect conditions but should a storm occur and perhaps a leg be unable to be raised, then longer legs with the ability to climb higher for an air-gap of over 15m will not be a luxury but a necessity.

The size of the cranes will not have to exceed l,500t in most cases. The heavier cranes would impact on the design and therefore the cost, making them too expensive for the majority of the work for which they are designed. GustoMSC have designed jack up vessels to have 50,000 jacking cycles in 20 years.

This amount of work increases the amount of fatigue and wear on the system which will continue to be a major design consideration, and therefore jacking systems require a more heavy duty design.

With all these factors price remains the limit and a major challenge for the future is to keep cost reduction in mind.

On other challenges facing their work they said that 'defining the next step', which is always difficult, 'in a maturing market', making it even more difficult, and 'convincing the wind farm owners and the turbine manufacturers that O&M will be the future'.

However these two men, with, perhaps, the future of WTIV's in their hands at GustoMSC, told Offshore WIND that they love challenges.

Dick Hill

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