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Seacor Marine's crew boat, the 180 x 32-ft. Jenny McCall, was built by Gulf Craft. In keeping with this rep- utation the Jenny, powered by four 1,800 hp Cummins KTA50 M2 main engines, will be equipped with the lat- est version of CSP Electronics controllable speed propul- sion. The system allows the operator or the dynamic posi- tioning system to achieve very precise shaft RPM against a constant engine rpm. The engines on the Jenny turn into Twin Disc 6848 gears with a 2.93:1 reduction. With the engines idling at 750 rpm, this equates to the 52x53-in. props turning at about 250 rpm. If all four engines are locked in at that rpm the boat will be traveling at seven knots. Even with just two engines and the idle set at 650 rpm, the DP system is working extremely hard with con- stant shifting forward and reverse to hold the vessel in position under a rig when handling cargo. With the slipping gear, the shaft rpm can be reduced on a continuous scale from 240 to 50 rpm. This allows for quiet steady handling with a smooth transition to lock up and then, at just over the 750 rpm idle, the turbo will kick in for maximum power. "While operation is sometimes compared to that achieved with a trolling gear there are major differences in accuracy, speed of response, gear protection, and heat rejection," maintains CSP Inc. engi- neer Ray Hatton, "Normally when a fisherman uses a trolling gear the vessel is moving through the water, when a boat is using our system in a dynamic positioning mode they are relatively still in the water so it is more like a bollard pull situation." Such conditions make additional cooling demands on the system, but Hatton explains they have allowed for this. He also maintains that the computer controlled sys- tem is so precise that it can control within plus or minus two rpm on the shaft. "In 2-4-ft. seas shafts may hold the vessel without going over the 240 rpm lock-up point, so the engines are sitting there idling at only 750 rpm. Some captains on the four other Seacor boats that have this sys- tem, report that in calm weather the system allows them to hold position with only two engines." 26 • MarineNews • December 2005 GREAT BOATS of 2005 Circle 224 on Reader Service Card Learn At The Helm Course Offerings www.chapman.org 1-800-225-2841 Professional Development Courses • USCG license Training through 200 GT • STCW 95, Basic & Advanced Firefighting, GMDSS, BRM, SSO, AB • Professional Mariner Training • Marine Surveying Recreational Courses • Chapman Powerboat Certification • ASA Sailing Certification including Celestial Navigation • Private Instruction – your boat or ours Circle 206 on Reader Service Card Jenny McCall: Crewboat Fitting one of the boat's 53 x 53-in. props. DECEMBER MN2005 4(25-32).qxd 12/5/2005 4:18 PM Page 26
