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Offshore Support Journal

Offshore Support Journal

Walk-to-work ship is an offshore wind and subsea hub

Tue 05 Sep 2017

Walk-to-work ship is an offshore wind and subsea hub
The design on which VOS Start is based provides high standard accommodation and work space with a 750 m2 clear deck and a walk-to-work offshore access system

The latest addition to Vroon Offshore’s fleet combines a stable, highly manoeuvrable platform with high-quality accommodation, onboard equipment storage and ease of access to offshore platforms  

July saw Vroon Offshore in the Netherlands hold a naming ceremony for VOS Start, the first of a new class of subsea/walk-to-work vessels that was purpose-designed and built to support offshore operations in the renewable energy industry and walk-to-work projects in the offshore oil and gas industry.

VOS Start started work for MHI Vestas Offshore Wind on the Walney Extension offshore windfarm in August, providing offshore logistic support, accommodation and walk-to-work services during construction of the Walney Extension offshore windfarm. A sister vessel, VOS Stone, has also now been delivered to Vroon by Fujian Southeast Shipbuilding in China, the same yard that built VOS Start.

Vroon Offshore has been active in the subsea support vessel market since 2000 and has gained experience in a wide range of operations and projects. Its subsea support vessel portfolio is based on vessel designs developed by the company’s performance and engineering department, reflecting client specifications, market requirements and substantial inhouse offshore experience. With VOS Start and VOS Stone, the company was aiming to meet the expected increase in demand for offshore transfer solutions.

The vessels offer accommodation and work space for up to 60 client staff (special personnel) and provide 750 m2 of clear deck space that can be fitted with a walk-to-work offshore access system whilst leaving ample space available for a variety of extra services. In addition, the vessels can be equipped with workboats and heave compensated davits.

Based on a design from Khiam Chuan Marine (KCM), VOS Start and VOS Stone are dynamic positioning class 2 (DP2) units that comply with the Special Purpose Ships (SPS) Code regulations. Working closely with Vroon Offshore and KCM, the Force Technology Design Institute helped the Dutch owner to optimise the vessels for efficient fuel consumption, whether sailing or in DP mode, and for onboard comfort for client personnel.

A number of walk-to-work vessels have been delivered since OSJ’s 2016 Annual Review issue, but few bring together so many innovations and so flexibly combine the ability to transport and accommodate personnel and equipment and provide access to offshore structures.

Since the vessel was delivered, much attention has focused on the motion compensated BM-Gangway system from Barge Master and active heave compensated crane and a 50-tonne capacity crane from SMST with active heave compensation, but VOS Start has many other features worthy of attention.

Containers holding equipment used offshore by windfarm personnel are housed on board in a warehouse area, within which remote-controlled trolleys are used to move items of heavy equipment around. There is also a fully covered workshop that can accommodate six containers.

The elevator that takes windfarm technicians up to the level of the walk-to-work gangway also services the warehouse, main deck level and the gangway.

The accommodation on board takes the form of 49 single cabins and 19 double cabins, all built and fitted out to a high standard. There is a 50-person messroom, large, fully equipped clients’ office with what the owner describes as an ‘urban’ feel and appearance, a conference room/cinema, fully equipped gym and 24/7 broadband on board thanks to a Ku-band satellite communications system.   

With a hydrodynamically optimised hullform tested by Maritime Research Institute Netherlands, VOS Start has a high level of manoeuvrability, with a total of three bow thrusters, one of which is retractable. The vessel has boat landings aft and on the starboard side of the vessel that enable crew transfer vessels to work with the ship and to be refuelled from it. 

Designed to have a high moment of inertia and low G forces, the vessel also has an anti-roll tank to further reduce rolling motions. The motion compensated gangway is installed at the centre of rotation of the vessel.

As highlighted above, VOS Start is the first application of the B-M Gangway, which was developed by Barge Master and Bosch Rexroth. Unveiling the motion compensated gangway to the press in June this year, Barge Master’s chief executive Martijn Koppert explained that the gangway will be mounted on a pedestal with an integrated elevator used to transport both people and pallet trolleys from the ship's deck and levels below to the level of the gangway. 

Bosch Rexroth sales manager offshore projects Boy Biermans said the gangway has telescopic sections that allow its length to be adjusted by an electrically powered winch. “This next-generation gangway is equipped with extremely fast sensors and control technology,” he said.

“Because of this, the system is able to compensate for wave heights of up to 3 m, resulting in an operating window that can be up to four times higher than other available systems in the market, making it unique.”

Vroon Offshore Services’ newbuilding superintendent Foppe Molenaar told OSJ “Continuous access is what makes this system unique compared to conventional offshore access systems. It ensures safe and efficient transfer of personnel whatever the sea conditions.”

VOS Start in brief

  • Hotel-type comfort and service (total 87 beds)
  • Client entertainment systems
  • Sky client office, library, gym and cinema
  • Dedicated client generator and 10 m2 client workshop
  • Extensive client email and data-communication facilities
  • 260 m2 clear deck area
  • 190 m2 covered warehouse
  • Dynamic positioning class 2
  • Compliant with SPS Code
  • Fuel-efficient
  • Motion compensated offshore access system
  • 500tonne active heave compensated crane
  • Optimised hull characteristics
  • Optimised anti-rolling tank
  • Improved seakeeping
  • Two super-silent tunnel bow thrusters (one retractable)


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