Offshore wind farm supply vessels driven by MAN power

MAN Engines for Commercial Shipping

The versatile workhorses of the offshore industry

Specific requirements and engine design in supply vessels for wind parks

Tidal Transit Eden Rose
More wind parks means more supply vessels in service

Supply vessels for offshore wind parks (wind farm supply vessels - WSV) are deployed for a variety of tasks and must fulfil a number of specific requirements. It is of the utmost importance to adapt the vessels to the requirements of the wind parks, which are being constructed at ever greater distances from the shore. Size, weight and versatility of the individual components are key factors when it comes to the layout of the engine room. Not only do these factors have an effect on the overall design of the vessel, but they constantly make themselves noticeable in day-to-day operation. Despite the variety of fields of application for WSV, the engines must also exhibit other, equally important characteristics. These include comfort, range, a good seakeeping ability and the vessel‘s capability to remain in position at the base of the wind turbine to allow technicians safe access.

The latter is accomplished when the captain accelerates in order to push the rubber lip on the bow of the vessel against the tower of the wind turbine. In order to press the ship against the tower, the engines are run at full capacity to ensure that oncoming waves do not carry the vessel away. It is merely raised and lowered to allow technicians to cross over to the ladder safely at the correct moment.

Tidal Transit Eden Rose
The vessel must remain in contact with the tower when manoeuvring

Manoeuvres like this place an unusual operating load on the engine. MAN has compared and analysed the load distribution in vessels like this in Great Britain. Diagram 1 shows an example of the load distribution typical to engines in this type of vessel. The engine idles for approximately one-third of the time (when the ship is in waiting position) and runs at 80 to 100 percent power for one-third of the time when accelerating or during the bollard push against the tower. The remaining third is distributed over the range in between while the vessel is manoeuvring and working amid the wind turbines.

These insights are invaluable for engine design and benefit the operator directly. In order to guarantee minimal fuel consumption, and therefore keep emissions low, optimisations need to be made where the engine is operated most. After all, consumption represents 90 percent of the costs during the lifetime of an engine, and therefore offers high savings potential.

Diagram 1: Example of a WSV load profile; Diagram 2: Torque curve for an MAN marine engine with plateau

The torque curve is closely related to consumption and load characteristics. Diagram 2 shows a curve typical for MAN engines, with maximum torque being achieved over a wide engine speed range. There are several reasons for an engine design like this: On one hand, a plateau like this makes a consistent, quiet and powerful acceleration possible. On the other hand, the wear on the engine is lower. This helps increase the lifespan of the individual components and therefore the entire drive system. Thanks to the torque plateau, the captain can keep the engine speed at its most efficient level without losing thrust. This is particularly useful when pushing a tower.

Engine room with MAN V-12 marine engine

Beside engine performance, weight and size play an essential role. A compact drive allows ship designers to keep the engine room as small as possible and creates more space for loads and crew. In addition, the smaller dimensions make access to the engine for service and maintenance purposes easier. Every kilogram saved in engine weight can, of course, be used to carry more loads. MAN pays particular attention to these characteristics, and its marine engines are setting the standard in this performance class.

Apart from efficiency, low consumption and the best possible engine design, other operating values are also important. Passenger and crew comfort is not only significant for pleasure cruises, but particularly decisive for working vessels. Technicians and crew spend up to 4,000 hours a year on the water, and it is the responsibility of the vessel manufacturer to ensure the best possible working environment. This includes comfortable seating and facilities as well as protection from noise and vibrations. These factors are not least relevant to safety, as well-rested and relaxed workers potentially cause fewer accidents. Marine engines made by MAN fulfil these requirements thanks to extensive experience in common rail systems. Optimised fuel injection not only ensures a high power delivery, but also a smooth run with lower noise levels and vibration.

Technicians and crew spend up to 4,000 hours on board per year

According to a white paper issued by TÜV SÜD in 2015: “As the offshore market matures, and wind farms are sited further offshore, so manufacturers of WFSV have recognised these changes in conditions and the new demands that will be put upon both vessels and their crews.” The market in Great Britain is a trailblazer in offshore energy and an ideal source of data and empirical values for helping deal with these conditions and requirements. The three principal tasks the vessels perform - the passage to the wind park and back, guaranteeing stability during the technicians‘ access to the tower and seakeeping ability during waiting periods - all exhibit different load profiles. MAN has, thanks to practical experience and data obtained with the help of its partners, succeeded in finding the best possible design for marine engines for installation in WSV both today and in the future.