Island Offshore’s newest vessel Island Crown, which was delivered in May, is of the same Rolls-Royce UT766 CD basic design as Island Crusader, which was delivered a year ago. Unlike the earlier vessel, Island Crown does not have the lean burn gas engines that marked Island Crusader out from the crowd of conventional PSVs, but it does have a number of other innovative features.
Without the huge gangway tower that stands on its stern port quarter and the somewhat larger than usual accommodation block topped with a helideck, Island Crown would look much like almost any other PSV of recent construction. Soon the gangway will be joined by a large active heave-compensated crane mounted on the pedestal already installed on the ship’s starboard deck, further disguising the origins of the ship.
Island Crown was indeed originally intended to be just another PSV, but part way through its construction its owner Island Offshore, believing that the PSV sector was losing its lustre, decided that the ship should be the first of a new breed of specialist offshore vessels. Instead of a lifetime of hauling equipment and supplies to and from platforms, Island Crown’s role will be aiding in their maintenance and repair as the very first ‘walk to work’ ship. Officially the ship is now a subsea support and accommodation vessel.
As Island Offshore’s owner Havard Ulstein explained to OSJ, there are several platforms around the world that need repair or maintenance but lack the accommodation on them for the required workforce. As a consequence, the platforms are required to cease any operations while gangs of workers take over what little living space is available and carry out the necessary work. After that, the workers depart and the platforms’ usual crews return to recommence normal operations.
With Island Crown, this obstacle is overcome in a quite novel way. The ship’s original accommodation for a normal PSV crew has been expanded and can now accommodate 100 people. Some of these are crew but the vast majority will be the workers carrying out the platform repair and maintenance.
The vessel will connect its motion-compensated gangway to the platform and the workers can walk between their accommodation on board and their workplace on the platform at will. This permits the platform’s normal crew to stay on board and for the platform to continue with its normal work unaffected.
The gangway was developed by Uptime, a joint venture between two Norwegian companies, Marine Aluminium and ICD. Svein Ove Haugen, marketing manager of Uptime told OSJ that this is the world’s first motion-compensated gangway installation and has been designed for operation in two main modes: long-duration connection, unattended by operators, and the push-on-mode, providing quick mobilisation.
With the push-on-mode, landings can be done very quickly against structures of almost any kind. The gangway is also the first Det Norske Veritas (DNV)-approved gangway meeting the new class requirements. The system has a multitude of redundancies and safeguards.
The gangway is telescopic vertically – with a minimum height of 12m above sea level and extending to 27m above sea level. The horizontal section also extends. A safe connection is made possible using Marine Aluminium’s landing cone which ensures that the gangway will be able to compensate for the relative movements between the connected parties. Hydraulics are used to manoeuvre the gangway into position after which they are disconnected allowing free motion of the vessel and minimal use of dynamic positioning (DP) to keep the connection safe.
The gangway was primarily designed to allow personnel to transfer between the ship and platforms but it is sufficiently strong to allow loads of 500kg to also be moved along it. It can also be used as a means of supporting hoses and cables when required.
Something else that marks the ship out from the other vessels in the Island Offshore fleet is the port of registry painted on its stern. Whilst the other vessels in the fleet operate under the Norwegian flag, Island Crown is registered in Nassau and sails under Bahamian colours. There is a very good reason for this. Island Offshore decided that the planned role of the ship would mean it should comply with special purpose ships (SPS) and mobile offshore drilling unit (MODU) rules rather than the cargo ship rules that apply to PSVs.
Because the ship would be essentially an extension of the platform it was moored to, the habitability rules for MODUs would need to be met. Furthermore, because the additional personnel were neither crew nor passengers, the ship would need to meet the SPS Code.
However, Norwegian regulations for SPS compliance state that the additional contractors onboard should have their place of work on the ship and, of course, this would not be the case. Island Offshore was therefore obliged to look further afield and settled on the Bahamas as a flag state that would allow the vessel to operate under both codes.
The decision to convert the ship came at a relatively late stage in its construction. The owner signed the contract for the ship with Vard (then STX OSV) in June 2011. In August last year, the hull arrived in Brevik from the yard in Braila, Romania, but within a month the gangway and the extra accommodation were ordered. The new two-deck accommodation structure was also built at Braila and arrived in Brevik in January this year.
The helideck is another fixture deemed necessary for the ship’s role. When connected to a platform, the ship cannot of course return to shore to change workers or crew but with a helideck, transfer of new workers is made simple.
The subsea construction aspect of the vessel is still to be realised and will centre around a new active heave-compensated (AHC) knuckleboom crane, which is to be delivered in November by Cargotec.
The crane will have a safe working load (SWL) of 8 tonnes with a 45m outreach increasing to 100 tonnes at 10m outreach. Until the new crane is delivered, a small substitute will be installed. A remotely operated vehicle (ROV) will complete the subsea equipment although the flexibility to add further systems in future is considered necessary as client demands change.
In common with most PSVs, the ship’s 96.8m length overall and 20m beam hull houses a number of tanks for water, mud, brine and dry bulk. Island Crown’s capacities in these regards are 930m3, 1,045m3, 620m3 and 310m3 respectively. The open deck area extends to 1,030m2. The tanks and cargo handling systems were all supplied by Rolls-Royce which also supplied the power plant and propulsion systems.
The vessel is equipped with a quartet of Bergen C25:33LP gensets each producing 1,740kW at 1,000 rpm. Main propulsion is provided by a pair of 2,500kW Azipull thrusters with the DP2 class dynamic positioning allowed for by twin 880kW tunnel thrusters and a similarly powered retractable azimuthing thruster at the bow. This arrangement provides the high level of redundancy required for the DP2 class dynamic positioning system. OSJ
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