Gulf Craft delivered the latest Seacor Marine crew boat the 180 x 32-ft. Jenny McCall. Seacor Marine, with input from the father son team of Norman and Joe McCall, is noted for innovation in this highly competitive market segment.
In keeping with this reputation the Jenny, powered by four 1,800 hp Cummins (CMI)
KTA50 M2 main engines, will be equipped with the latest version of CSP Electronics controllable
speed propulsion. The system allows the operator or the dynamic positioning 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 constant 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. (CSPI)
engineer 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 system 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 system, report that in calm weather the system allows them to hold position with only two engines."
Joe McCall explains that on the boats with this system, "Due to the constant speed of the engines while maneuvering, we have seen a reduction in the engine repairs. Constant acceleration / deceleration of the engines while maneuvering increases the thermal cycling of the engine as the vessel maneuvers. CSP has allowed us to run the engines at constant speed so we have reduced the wear on the engines. We have also seen a significant reduction in fuel consumption as CSP allows us to maintain position using less horsepower than conventional propulsion systems. This saves our customers money." The system is tied in with the vessel's CSP Inc. integrated electronic controls These provide a full vessel monitoring system that allows all alarms and indicators to be integrated into a single display. The system will alert the captain with either a visual indication, voice annunciated audible alarm or both. It also has an e-mail capability that can be utilized to notify a shore base of the alarm, and can take immediate control to alleviate the problem if conditions warrant.