New Propulsion System Improves Uptime, Power

Thursday, August 16, 2001
The repower of Brother, a 140-ft. aluminum offshore crew/supply vessel with Cat 3508Bs, has reportedly improved efficiency more than 20 percent, and helped to decrease downtime significantly, according to Mike Dickinson, Eastern Division general manager for Graham Gulf Inc. of Bayou LaBatre, Ala. Graham Gulf currently operates five 140-ft. aluminum offshore crew and supply vessels in the Gulf of Mexico. All of the boats were designed and built by C&G Boat Works, a sister company of Graham Gulf, also located in Bayou LaBatre. Brother entered service in January 1998 powered by another manufacturer's 16-cylinder engines rated at 1,100 bhp. After more than two years of operation, Graham Gulf decided that the engines were not performing at the level required for the job. Two different engine models were considered for the repower. One manufacturer's engines were eliminated from consideration because they would have required extensive hull modifications, making it cost prohibitive. After discussions with local Cat Dealers and with corporate Caterpillar personnel, Graham specified four Cat 3508B engines rated 1,200 bhp at 1,800 rpm. ZF 2.33:1 marine gears replaced the previous 2.5:1 gears. Required changes during the repower included new water piping from the engines to the coolers, new engine controls and gauges, and new blowers to increase combustion and ventilation air flow through the engine room. Pipe diameter for the water-injected stern- discharge exhaust system was changed from 6 in. to 12 in. Low-end maneuvering was also a major concern coming into the repower, says Dickinson, because 60 percent of the vessel's operating hours are spent maintaining station while offloading supplies. "The Brother's original electronic engines required full throttle to maintain station, but the Cat 350Bs are doing the same job at quarter-throttle: When we put the engines in gear now, the boat moves. And there's less chance of damage to the vessel because the boat can do what we ask it to do," says Dickinson. While Graham Gulf considers improved vessel speed as secondary to improved handling capabilities, the speed increase is significant as well. Brother averages 5.5 hours per day at full-throttle transport speed, serving oil rigs located south of Dauphine Island, about 80 miles out from Bayou LaBatre.
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