Offshore ship goes deeper than beforeVessel & ROV News // September 22, 2000
When it enters service in June 2001, the newbuilding will, claims its owners, be the most sophisticated survey/ROV vessel available, providing a combination of excellent seakeeping characteristics, with reduced downtime, increased deck space, and highlycapable ROV launch equipment and craneage.
Designed to be as flexible a platform as possible, the newbuild also has a large back deck area, has a helideck capable of accepting a Super Puma helicopter, and is capable of operating worldwide in water depths of up to 3,000m.
The newbuilding contract was placed on the basis of a time-charter agreed with Fugro-UDI, part of the Marine Survey Division of the Fugro Group, which specialises in all aspects of offshore survey and positioning systems. DOF says the contract arises asa result of the excellent performance of the MV Skandi Inspector, which has been on time charter from DOF to Fugro-UDI since she was delivered in March 1999.
"The market for this type of vessel is developing quite quickly", explained John Meaden, Managing Director, and Mark Derry, Marketing Director, at Fugro-UDI in Aberdeen. "Skandi Inspector has is an exceptionally manoeuvrable design that can carry out operations on subsea installations and platforms within the standard 500m safety zone", explained Derry. "In this respect, her performance has been exceptional, but the performance of the newbuilding will be more exceptional still, and the fact that she isa newbuild rather a conversion like Skandi Inspector, has enabled us to optimise the design throughout".
A comparison of the newbuilding and the converted ship - although itself highly capable - reveals some interesting features. It also highlights how DOF and Fugro have used the experience gained whilst operating Skandi Inspector to good effect, and how inthe company's thinking has moved on in the space of just 18 months.
The survey company plans to use the newbuilding on the growing number of deepwater projects around the world, and she will be assigned to work not just in the North Sea, but off West Africa and off Brazil. She therefore differs from the Skandi Inspectorin as much as she can work at depths of up to 3,000m, compared to the 2,000-2,500m of the Skandi Inspector.
The newbuilding is based on the MT6002 design developed by Marin Teknikk in Norway, a further development of DOF's four existing vessels. Designed to provide ROV, survey, geophysical, geotechnical and construction support services, the newbuilding will be 83.85m overall, 76.80m between perpendiculars, with a breadth of 19.70m, and will have accommodation for up to 80 persons.
She will be equipped with a 5.5m x 5.4m moonpool, a 19.5m x 19.5m helideck for Super Puma class helicopters, a heave compensated crane with lifting capability of 50t at 10m radius, and will have a cargo deck of 634m2.
Whereas Skandi Inspector has direct drive machinery in the form of two 2,407hp MaK diesel engines driving a pair of variable pitch main propellers, plus bow and stern thrusters, this latest addition to the DOF fleet will have a much more sophisticated arrangement.
Classed by DNV, she will be fitted with four 2,500kW main engines in a diesel electric arrangement, the engines, as yet unspecified Caterpillar models, providing a total of 10,000kW.
The electricity generated by the engines will be used to drive a total of five thrusters. These include a pair of electrically driven azimuthing thrusters aft, which serve as the main propulsors, plus a pair of tunnel thrusters and a single azimuthing thruster forward, all of 1,000kW.
In contrast to the newbuilding, where all of the propulsion and on board power requirements will be met by the relatively compact diesel electric plant, the demand for electrical power on board older vessel is met by a combination of auxiliary generatorsand shaft generators. Apart from her prime movers, the Skandi Inspector was therefore also fitted with 1,000kVa auxiliary generators, and a pair of 1,500kVa shaft generators that provide the electrical energy required on board, during her conversion.
Derry says the diesel electric arrangement will be 30-40 per cent more fuel efficient, and much quieter than conventional machinery. Combined with a sophisticated dynamic positioning system a suite of thrusters, it will provide the newbuilding with a station keeping capability that far exceeds that of the already highly manoeuvrable Skandi Inspector. Being much quieter than conventional direct drive machinery, it will also make for better living conditions for the crew and other on board personnel.
Like Skandi Inspector, the newbuilding will have a Simrad DP 21 dynamic positioning system and a HiPAP acoustic positioning system, but as Derry explained, the station keeping capability of the newbuilding - designated ERN 99, 99, 99 - comfortably exceeds that of the converted ship.
The ERN number describes the ability of a ship to maintain station in different wave heights, currents and winds - the already highly capable Skandi Inspector is an designated as an ERN 80, 90, 80 ship, explained Derry, able to work in the most taxing conditions, but the newbuilding will be capable of working in 99 per cent of the conditions she encounters at sea.
Though not much longer than the Skandi Inspector - being 84m overall compared to the 81m of the earlier ship - the newbuild is a significantly broader, having a breadth of 20m compared to just 18m in the Skandi Inspector. This provides another highly important benefit for any type of offshore ship - significantly more deck space. "The Skandi Inspector has a 540 square metre main deck, whereas the newbuilding will have in excess of 600 squares metres of back deck", explained Derry.
Like the Skandi Inspector, the DOF newbuild will be equipped with a fully heave compensated ROV launch system, and will be capable of launching and recovering the ROVs with which she is equipped in up to Sea State 8.
Having a heave compensated launch system ensures minimal damage to the ROV and umbilical in severe weather, and ensures that ROV operations can continue unhindered even in extreme weather conditions - this highly capable launch system also translates into minimum transit time for the ROV to and from its objective, and maximum time on the bottom carrying out work.
The launch system on the Skandi Inspector has a purpose-designed traction winch which enables the ROV to be deployed quickly and efficiently to 3,500m, and its deployment and recovery speed is twice that of 'over-the-side' or most other conventional moonpool launch systems.
The newbuild will be equipped with a very similar system, but as Derry explained, another noteworthy feature of the ship not found on the Skandi Inspector is a 5.5m x 5.4m moonpool that can be closed once the ROV has been deployed. The moonpools on bothvessels are completely covered - in order to enable ROV operations to proceed whatever the weather conditions - but this useful additional feature on the new ship should eliminate many of the well-known problems associated with water entering the ROV hangar from beneath it in heavy seas.
When she was converted in 1998/1999, the Skandi Inspector was equipped with what was, at the time, a new generation of heave compensated crane developed by TTS-Norlift of Bergen in Norway. The design objective of the crane was that it should be capable of handling deepwater packages at optimum speed. It was configured for operations in water depths of up to 2,000ft, and can handle 50 tonnes lifts in water depths of 600m, or 20 tonnes 950m or 12 tonnes at 2,000m when fitted with a deepwater winch unit.
Compared with the Skandi Inspector's crane, the somewhat more capable heave compensated crane selected for the newbuilding is capable of 50 tonnes lifts at a 10m radius, 30 tonnes at 16m radius, 10t at 33m, and can lift 15 tonnes at 2,000m. Smaller loadscan be safely lowered and recovered at depths of up to 3,000m.