Today’s crew/supply boats are longer, wider and carry considerably more main deck cargo and a greater volume of transferable liquids than just a few years ago. In addition, these vessels are operating in deeper water, farther from shore and in weather that is often marginal at best.
Considerable diesel power is required for these heavily laden crew/supply boats to operate at 24 to 26 knots. Shipbuilder Gulf Craft LLC, Patterson, Louisiana, U.S.A., is building a series of 57.9 m by 10.4 m crew/supply vessels for Seacor Marine, Morgan City, Louisiana. These vessels feature five main propulsion engines, two of which power generators, while the three remaining engines run thrusters and other auxiliaries. In total, there are 10 diesel engines generating 7700 kW of power onboard these new crew/supply boats.
Gulf Craft received an order to build four of these vessels that will keep the shipyard busy through much of 2011. They will be the longest, most powerful monohull crew boats the company has built to date. “The design has evolved into two slightly different versions,”said Joe McCall, vice president of Seacor. “One version cuts the number of passengers to 36 but gives the vessel the ability to carry about 1000 barrels of liquid mud. The more standard vessel can carry 60 passengers in the main deck cabin,” McCall said.
This new series uses five Cummins KT50A engines, each rated at 1342.8 kW, for a total of over 6700 kW of propulsion power. Each engine is coupled to a Twin Disc 6848 reduction/reversing gear outputted to a 12.7 cm stainless-steel shaft and a Michigan four bladed controllable pitch 137 cm by 134.6 cm propeller. The port, starboard and center propellers each have independently controlled rudders for precise steering control.
A Cummins QSM-11 engine powers a Thrustmaster azimuthing bow thruster, while another QSM-11 drives two tunnel bow thrusters, also supplied by Thrustmaster. The vessel is set up for DP2 operation and the multiple bow thrusters provide the redundancy needed to ensure the strict operating conditions of DP2 will be met. Electrical power comes from a pair of 135 kW generators driven by two Cummins 6CTA engines. The 10th engine, also a 6CTA, powers the bulk compressor.
The many redundant systems throughout the boat are the key to DP2 certification. For example, there are three rudders, so if one fails two are available for steering. Also, twin generators ensure an uninterrupted flow of electric power, the switchboard can transfer electrical loads to one generator if the other fails, and the computers and other primary DP components in the wheelhouse are backed up. Wind birds, vertical reference units, compasses and other DP gear are also duplicated.
What is not duplicated, however, is the sheer hauling capacity of this new series of 57.9 m crew/supply vessels. Rig water capacity is 263 m3 and there are tanks for 150 m3 of fuel oil and 67 m3 of dry bulk material in deck tanks. Deadweight is 457 metric tons. The main cargo deck is 37.5 m by 8.5 m and can carry 406 metric tons. Maximum speed is 26 knots with a 23 knot cruising speed and a 20 knot economy speed. Fuel consumption is 1552 L/hr at 26 knots, 1363 L/hr at cruising speed and 984 L/hr at 20 knots. Discharge rates of transferable materials are 159 m3 per hour of drill water at 79 m and 79 m3 of fuel per hour at 73 m.
This new series of vessels is loaded with high-tech systems including innovative gear controls. However, one problem with the large multi-engine crew boats is that when idling, the engines are turning at 750 r/min and the propellers at 250 r/min. If all five propellers are locked in at that rate, the boat will still be traveling at about 7 knots, making the DP system work hard with constant shifting into forward and reverse under a rig transferring cargo. With a gear controller from CSP Electronics, Morgan City, the shaft speed can be reduced on a continuous basis to 50 r/min, making it a lot easier to keep the vessel in a DP mode.
“Due to the constant speed of the engines while maneuvering, we have seen a significant drop in fuel consumption, as well as in wear on the engines. Saving fuel saves our customers money and less wear on the engines relates directly to our repair costs,” said Seacor’s Joe McCall.
This system is tied into the CSP integrated electronic controls system, which provides full vessel monitoring that allows all alarms and indicators to be integrated into a single touch screen display. There is also a CCTV system that provides coverage of critical areas of the boat as well as a lood light system that illuminates the main rear deck in times of low light. Most of the pilothouse electronics are made by Furuno, including a pair of radars, Navtex, AIS and SSB. The DP system is the Kongsberg DPS2 K POS and the chart plotter is by Coastal Explorer, with Garmin supplying the GPS and ICOM the VHF radios. These vessels will be U.S. flagged and have ABS classifications of ABS +A1HSC Crewboat, +AMS and +DP2.
The U.S. Coast Guard Certificate of Inspection classifies these vessels as both a Sub Chapter T Passenger Vessel and a Sub Chapter L offshore supply vessel, with flammable/combustible cargo allowed on deck. The vessel also has F1F1 firefighting capability.
The first of the four vessels to be delivered is the Paula McCall, set to join the Seacor fleet in the fourth quarter, 2009. This will be followed by two vessels in 2010 and the fourth in 2011.