An oil-filled stainless-steel tube, in which the propeller shaft rotates supported by roller bearings, hydrodynamic journal bearings, and thrust bearings reduces drag to an absolute minimum.
The thrust bearing housing, at the inboard end of the tube, bolts to the hull transferring thrust from the propellers to the vessel structure and not through the transmission and engine.
Flexible isolators located between the ‘BOSS’ system, the vessel’s hull, and the strut absorb thrust loads as well as significantly reducing noise and vibration
The enclosed shaft arrangement eliminates turbulence and drag, referred to as the ‘Magnus Effect’, so the water flow to the propeller is far less disturbed compared to a shaft spinning in open water. Inefficiency and drag created by cutlass bearings and shaft misalignment are also eliminated.
The system is completed with a Cardan shaft connecting the ‘BOSS’ system to the transmission reducing the need for very accurate and time-consuming engine alignment. An oil reservoir located in the engine room allows easy monitoring of the oil level.
Conventional shaft installations rely on anti-vibration mounts to absorb engine and transmission vibration as well as propeller thrust. The ‘BOSS’ system removes the thrust from the mounts so they can then be optimised for absorption of engine vibration and torque, reducing the transmission of vibration into engine beds and the vessels structure.
The combination of taper and needle roller bearings, the non-rotating full-length shaft casing, the resiliently mounted thrust bearing and strut, and the optimised engine mounts all contribute to the very significant reduction of noise and vibration, typically over 50%
In addition, the reduction of mechanical losses to only 2%, providing valuable extra power for propulsion, and fuel consumption reductions of circa 8%, as verified across a number of in-service case studies, are very valuable considerations when specifying your shaft system.