382 September 2006
Diesel Electric: The Rigdon Advantage
Since Rigdon Marine introduced their first Cummins-powered diesel electric platform supply vessel (PSV) in 2004 (Hotips#259), the technology has been incorporated in similar vessels from Norway (Hotips#291) to China (Hotips#313). In January 2006 Rigdon Marine announced plans to build ten new 654 Class PSVs at Bollinger Shipyards in Louisiana. (www.bollingershipyards.com 19/01/06 press release)
At190x46x18 feet these are smaller than the earlier 640 Class PSVs that are 210x54x19 feet. They also bear testament to Rigdon's satisfaction with the diesel electric technology. Asked about these advantages, Jim Whitley, Rigdon's director of technical services, explained that there are three primary advantages: fuel efficiency, redundancy and flexibility of installation. In terms of fuel efficiency Whitley explained that conventional geared drive engines typically loose only 5 to 6% of their energy between the flywheel and the props. Diesel electric with the introduction of the electric generator and electric drive motor between the engine and the prop actually looses 10 to 12% of its power. For a vessel, such as a tug, that is dedicated to long runs at full RPM and little or no time at idle the conventional propulsion has advantages. However in a vessel like a PSV that spends much of its time at reduced power idling off a platform or at the dock, the ability to shut down one or two of the engines while continuing to hold station more than makes up for the reduced efficiency to deliver significant fuel savings.
The larger 640 Class vessels have three diesel-powered generators including two 1,825 kW (2,447 hp) generators powered by Cummins QSK60 engines and one 910 kW (1,220 hp) generator powered by a Cummins KTA38 engine. One of the 640s was contracted to do marine seismic work that involved many hours of moving between waypoints laying cables at only 2 or 3 knots. The two big QSK60 engines were shut down and the boat made way on only the single Cummins KTA38 powered 910 kW generator. The boat can make seven knots on the smaller engine.
The new 654 Class PSVs will be powered by two 1235 kW electric generators each powered by Cummins KTA50 diesel and one 410 kW generator powered by a six cylinder Cummins KTA19. This will make possible similar fuel savings to those currently enjoyed by the ten 640 Class vessels already in service.
The three electric generators will drive two Steerprop azimuthing drives, one Steerprop fixed drice and two bow thrusters. With three electrical generators each able to provide power to the five drives, the level of redundancy meets and exceeds all of the requirements to qualify as DP2 vessel. Even if two of the three generators went down, the third would still be able to provide power for the propellers.
The new 654 Class vessels currently building at Bollinger Shipyards take the fullest advantage of the flexibility of placement of the engines. On these vessels, the engine room will be on the main deck level, leaving the entire hull available for cargo. This gives a 190 by 46-foot vessel the hold capacity of a much larger vessel. These 1850 dwt vessels will carry 4,000 barrels of liquid mud with a split system and round tanks. With the engines mounted forward on the main deck there is no longer a need for the long runs of exhaust piping that have been common on recently built supply vessels with their engines mounted aft.
The advantages in fuel savings, redundancy and flexibility of engine location are clear to vessel owners in the worldwide oil industry support services. Cummins powered diesel electric vessels are now being built in both European and Asian shipyards.
Download Comparison of GPA 654 and GPA 640 PSV.
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