The infield support vessel (ISV) ‘Siem Moxie’ will be the first Ulstein X-BOW workboat to be fitted with two Voith Schneider Propellers (VSP).
X-BOW vessels are characterised by the absence of a bulbous bow. Their bow slopes backwards above the water line which results in reduced resistance and improved wave slamming characteristics on the foreship.
Designed for specific tasks in wind farms in the North Sea as well as in the Atlantic, the work boat with a length of 74 meters and a beam of 17 meters will be fitted with two electronically controlled VSP of the size 28R5 ECS/234-2. They have a propulsion power of 1,850 kW each and will be arranged in the stern. The two Voith Schneider Propellers will also be used for active roll stabilization as well as for dynamic positioning (DP class 2). The entire propulsion system as well as the DP system will be controlled centrally. The interfaces for propeller and roll stabilization control will be provided by Voith.
For the ‘Siem Moxie’, model tests were carried out at the Hamburg Ship Model Basin. The favorable interactions between the VSP and the X-BOW design result in lower vibrations, a reduction in fuel consumption and therefore in reduced emissions. The new workboat will not only allow faster transfers of the up to 60 crew to the wind farms but will also ensure more efficient operation under DP conditions. Given the more stable position of the vessel, even adverse sea and wind conditions still permit work to be carried out on the 200 square meter work deck as well as close to the offshore units.
Once the ‘Siem Moxie’ has reached her operating site, engineers can safely cross to the individual wind turbines using a gangway with a wave compensation unit – a process during which the advantages of the Voith roll stabilization and the two VSP are at their most impressive.
In addition to wind farm tasks, the Norwegian owner Siem Offshore AS intends to use the vessel for cable laying operations in the North Sea and in the Atlantic. The vessel is currently being built by the Fjellstrand AS shipyard in Norway and is due to be delivered in the Spring of 2014.