"Limo" RoRo for Middle East
Building a small RoRo ferry for a Middle Eastern client proved an interesting challenge for the Scottish yard, Corpach Boatbuilding Co., as the owner called for a vessel capable of carrying two limousines that were able to be loaded from either a concrete ramp or a sandy beach. The ferry had to have shallow draft at both ends, be simple to operate with a small crew, and fulfill a demanding build specification. A design by a local Scottish firm of naval architects, A.G. Salmon & Co., resulted in a hull shape which met the draft requirements of 2.7 ft. (0.85 m), propeller protection, stability, and load carrying capacity. At 55.7 ft. (17 m) x 15.5 ft. (4.75 m), the vessel — named Shilala — has a double articulating ramp fitted forward and aft with all remote, auto-sequenced controls in the wheelhouse. The latter is elevated and offset to starboard with 360-degree visibility, and a center island console from which the helmsman can easily steer when facing either forward or aft. Hull construction is of 6-mm steel plate, longitudinally framed with two watertight bulkheads and several deep ring frames. The wheelhouse is also of all-steel construction, with stowage space and engine room access via watertight doors below wheelhouse level, above the main deck. Outfitting is robust, including 3.2-ft. (1-m) high bulwarks with handrails on the car deck, and D section fendering on the mid-length section. Lashing points are fitted for security and lifting eyes are incorporated for shipment and craneage.
Choosing suitable propulsion machinery led the design team to U.K.-based Kort Propulsion. An all-hydraulic package was devised, using two Vickers piston pumps in tandem, driven directly by a 300- hp Scania diesel. The system powers two propulsion units de-rated to about 100 hp each, together with a 30-hp bowthruster and bow and stern ramps, which each require about 6 hp. Three Danfoss proportional valves receive all the output from the two pumps, provide a feedback signal into the pumps to monitor their output to the level required, and monitor the hydraulic fluid to the five services according to the signals received from the wheelhouse. The complex engineering necessary to achieve this is hidden in a small number of integrated assemblies, some of which have been specially designed and manufactured, resulting in a simple layout and minimum pipework.
The ramps are long in relation to the vessel, and are more complicated than typical vehicle ferries.
This is because the outer leaf stows underneath the inner leaf in order to avoid a height restriction on the car deck. Lowering or raising the ramps is a sequenced operation activated by pressing a single button in the wheelhouse and the system includes provisions for the ramps to change angle while lowered to allow for tide or turbulence. Care has been taken to ensure smooth lowering and avoidance of the instability which is possible with proportionally controlled sys- Circle 2 4 7 on Reader Service Card tems.
Kort Propulsion supplied the complete hydraulic package, including pumps and valves, for the propulsion motors and switches, with Corpach carrying out installation. Control for the propulsion units is simple via a twin-head Kobelt system, operating proportional valves to vary propeller speed. Kort's bowthruster units are belt-driven from hydraulic motor, so the drive housing can be used as a main or auxiliary propulsion unit. Two KT170 propulsion units and KT30 bowthruster unit have been fitted. Currently completing sea trials at Corpach, Shilala is to leave for a five-day delivery trip to Hull for onward shipment to Dubai.