Demand for vessels capable of accommodating offshore wind technicians and enabling them to ‘walk to work’ using a motion compensated offshore access system is growing, as contracts awarded to Østensjø Rederi in 2016 demonstrate.
On 27 April 2017, Gondán shipyard launched Edda Passat, the first of two service operation vessels (SOVs) it is building for Norwegian shipowner Østensjø Rederi. Both SOVs are being built to the UT 540 WP design by Rolls-Royce Marine, this being the first Rolls-Royce design for the fast-growing offshore wind energy industry.
The vessels will be equipped with an Uptime 23 m heave compensated walk-to-work gangway, a 3D motion compensated crane and a crew transfer vessel handling system with bunkering facility. In addition to the gangway, an 11 m daughter craft will allow for the safe transfer of maintenance technicians to offshore wind turbines. Once completed, the first vessel will be chartered to Dong Energy. The second vessel it has under construction is also for Dong Energy and will service the Hornsea Project One offshore windfarm in the UK.
The first newbuild is a dynamic positioning class 2 (DP2) SOV with excellent station keeping capability. It will have 60 single cabins and accommodate up to 40 wind turbine technicians in addition to a marine crew of 20. The 81.10 m vessel will have a beam of 17.0 m and work out of an operations base in Grimsby on the east coast of the UK. It was designed by Rolls-Royce in close co-operation with Østensjø Rederi and Astilleros Gondán in Spain, who are building it. F3 Offshore in Germany was engaged by Østensjø Rederi to act as the broker for the deal.
The contract for the first vessel was placed after Østensjø Rederi was awarded a contract to provide an SOV for Dong Energy’s Race Bank offshore windfarm in the UK. The contract awarded to the company by Dong Energy is for five years firm with five optional years. Commencement is 1 September 2017.
Describing its first venture into the SOV market, Rolls-Royce said the vessel was designed with a focus on seakeeping capability, excellent station-keeping performance, improved comfort and safety on board and reduced fuel consumption. As well as designing the vessel, Rolls-Royce will supply the diesel-electric main machinery, consisting of frequency controlled electric driven azimuth thrusters, super-silent mounted transverse thrusters, DP2 dynamic positioning system, power electrical system, deck machinery and the latest generation Acon automation and control system.
The SOV will operate from a new offshore wind hub in Grimsby. The new SOV will initially support operation and maintenance of Race Bank, which is under construction 17 miles off the Norfolk and Lincolnshire coastlines. Some components needed to maintain wind turbines will be stored in a warehouse on the hub site. Other equipment will arrive from manufacturers on a ‘just in time’ basis to be loaded onto the new vessel.
Once mobilised, the SOV will spend up to 28 consecutive days on station at the windfarm, where it will be able to service six to eight wind turbines each day. Crews of technicians from Dong Energy and turbine supplier Siemens will work on a two weeks on, two weeks off shift pattern.
With the SOV in position, technicians will walk safely to work from the vessel’s deck to work on the wind turbines using the motion compensated gangway, thus removing the need to climb up and down vertical access ladders as happens when traditional crew transfer vessels push on to the foundation of a turbine. The SOVs will incorporate a containerised warehouse for the storage of equipment spares, tools and consumables.
Below the weather deck aft is a large area for containerised loads and stores. Their floors are level with the main deck, which is strengthened for forklift truck operation. Close attention has been paid to logistics and workflow in the vessel design. Technicians leave their cabins, eat breakfast in the messroom, then go along a short route to the work area to put on protective equipment. They then collect trolleys of equipment needed for the day’s task, which have been pre-prepared, before taking the lift up and walking to work over the gangway.