The Netherlands: Voith and DOI Increase Stability of Turbine Installation Vessels
In cooperation with Voith, Dutch Offshore Innovators BV, (DOI) developed together a new concept for economical operations of a wind turbine foundation installation vessel.
The so-called TFliner concept is a move towards compact design and simplicity, which drastically reduces construction costs. An increase in operability is offered by the Voith Roll Stabilization (VRS) feature of Voith Schneider Propellers (VSP). This was the reason for VSP being chosen as propulsion system for sailing and station-keeping.
The aim of DOI, a young company of naval architects, was to design an economical vessel. Therefore both the construction costs as well as the operating costs had to be kept to a minimum. For the operations, innovative installation techniques have been developed that reduce the size and therefore the costs of the mission equipment. The first vessel has been designed to carry monopiles of up to 75m in length and 900t in weight. For the handling of the monopiles the vessel can be equipped with a system of rollers and translators that move the monopiles over the deck. Subsequently, up to 16 transition pieces can be carried on the main deck of the vessel. The transition pieces can be installed directly using the motion- compensated crane with a capacity of 350t. Alternatively, the vessel will be fully equipped for installation of jacket type foundations, comprising state-of-the-art tools for installation and piling of foundation piles, and installing the jacket. In this design version the ship will carry two jackets and thus reduce the overall construction time.
As construction vessels for offshore units need to retain their manoeuvrability at all times and keep the dynamic positioning capability even under extreme weather conditions, DOI decided in favour of the Voith Schneider Propeller as a main propulsion system. Due to its capability of redirecting the thrust by 180 degrees within 5 seconds, the VSP allows dynamic positioning in a most economical way.
Furthermore, the propulsion efficiency while sailing is substantial higher compared to other steerable thrusters, leading to less fuel consumption and less CO2 emissions. The Voith Roll Stabilization will reduce the ship’s roll motion while sailing and while station-keeping, thus increasing the limit of maximum significant wave height up to which safe operations are possible and leading to additional income for the owner. The redundant design of the entire drive system ensures high safety. This design keeps the vessel under control, even if only one propulsion system is available.
For station-keeping in the offshore wind energy industry, a DP-2 class notation is widely accepted. Dynamic positioning is done with the three 2.5 MW Voith Schneider Propellers in the aftship and three Voith Inline Thrusters in the bow. The most important advantages of the Voith Inline Thrusters are significant reductions of noise and vibration levels, as well as maintenance-free operations. To extend the operational envelope, the vessel is designed with an anchor mooring system.
In order to have good control over the stability of the vessel in a wide range of loading conditions, the vessel features a hull shape with a very narrow waterline and an upper part of the hull that flares out to a very wide deck. By adding ballast during transit, the vessel can meet all stability criteria, even with a deck cargo that is very high in weight, windarea and VCG. By deballasting the vessel to a lower draught during installation operations, the GM can be kept at a constant low level over a number of installation operations, which reduces motions, and increases the efficiency of the active Voith Roll Stabilization.
Source: maritimebyholland, September 07, 2011