Double-Engine Diesel Drive for Yachts
Yachts, ships larger than 10m in length, are normally driven by two-engine units, whereby the gearbox is directly coupled to the diesel engine (closed-coupled) or the connection between engine and gearbox is made by a coupling and a cardan shaft (V-drive). The diesel engines used in such applications are characterized by their high power density combined with low weight, and make high demands on the couplings used in terms of optimization of rotational vibrations as well as the required displacement values.
The POD Drive is one of the most efficient propulsion systems, specially made for twin-engined pleasure crafts of 50 to 75 feet length, and in triple or quad configuration suitable for yachts up to 120 feet length, where each pod can be driven by a diesel engine up to 1200 hp. This system offers an increased propulsion efficiency, compared to traditional drive lines, resulting in a speed increase and a significant reduction of fuel consumption at cruising speed. Products from VULKAN also find application in these modern drive systems.
On fast sport boats with a length under 10 m (33 ft) the so-called Z-drive is frequently the mode of propulsion, which is meant to combine the advantages of inboard motors with those of outboard motors - low noise levels in combination with high maneuverability. The real drive (propeller and transmission) is located outside the boat. Generally, the connection between the engine and the transmission is made through an flexible coupling in association with a cardan shaft.
With regard to the drive units, the mega yachts may be most closely compared to fast ferries. For the most part, fast-running, highly powered, but lightweight diesel engines are employed. The drives, usually diesel-mechanical, drive jets or propellers via lightweight reduction gears. The requirements for comfort are even higher; a special elastic mounting system (e.g. elastic engine as well as gearbox mounting) ensures maximum noise attenuation. This and certain specifics of shipbuilding require the use of specially adapted, high misalignment and structure-borne noise reducing couplings between the main engine and gearbox, as well as at the gearbox output to the propeller shaft.
Diesel-Mechanic Drive with Integral Shaft Support
With diesel-mechanical drive units, where there is an angular displacement between the diesel engine and the gear box (so called V-drive or remote drive), cardan shafts are normally used between the diesel engine and the gear box, which compensates this angular shaft displacements. The diesel engine has to be protected from the reaction forces generated by the angular displacements of the cardan shafts. The integral shaft support from VULKAN provides optimum drive protection, due to its design principle. Through the internal bearings of the ISS, the reaction forces created from the angular displacement of the cardan shaft are transmitted through the coupling housing into the engine block, the motor’s crankshaft bearings remain unaffected by these forces, which in turn means an optimum protection for the engine.
The Flexibly Mounted Auxiliary Drive
Supplementing the known rigidly mounted auxiliary drives, flexibly mounted drives are today a common alternative. Depending on the consuming power of the generators, and thereby the size of the four-stroke diesel engines, for comfort reasons either only the diesel engines are elastically mounted, or the engine and generator are rigidly mounted on a common frame, which is elastically mounted to the ship’s hull above.
Considering the first named category, were the engine is able to move against the attached machinery, the elastic behavior of the coupling needs a special focus. Couplings used in these applications need to be able to compensate the engines movement by a relatively soft radial stiffness. VULKAN offers a broad range of couplings capable for flexible mounted auxiliary drives including RATO S, RATO R and VULKARDAN F couplings. Together with the in-house manufactured elastic mounts, VULKAN delivers the complete solution for an optimal tuning of auxiliary units.
More than this, VULKAN delivery program exceeds that of a common part supplier. In house 6- or 12-Degree-of-Freedom-Calculations allow the best suitable engine mounting in respect to comfort and engine safety. Together with the in-house torsional vibration department, all elastic parts as couplings and mounts can be perfectly harmonized for the best results in terms of vibration and noise reduction.