Propeller shaft enclosure system

By Keith Henderson at July 09, 2010 16:34
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There is a patented device claiming to give between 6 to 10 per cent increased efficiency to the propulsion system applying mainly to planning hulls with inboards. The BOSS (Bolt On Shaft System) as it is called, basically is a tube that encloses the immersed part of the propeller shaft and combines it with a seal and thrust bearing that is mounted directly on to the hull. The self contained unit eliminates through hull sealing and alignment difficulties, and allows the gearbox and engine to be mounted free of thrust considerations. The propeller end of the tube is supported by a P-bracket type of arrangement. For the boat builder, installation times are substantially reduced and the built-in watertight shaft seal ensures a dry bilge. For the user, the reduced losses give the benefits of lower fuel consumption, improved range or a higher top speed. It’s available for shaft diameters of one to four inches (25 – 102mm) and is claimed to lower propulsion noise and vibration.
At one of the trade shows I was visiting there was a patented device claiming to give between 6 to 10 per cent increased efficiency to the propulsion system. It mainly applies to planning hulls with inboards but when one looks at all the patrol boats and various, not to mention recreational craft it does offer substantial savings to a very large worldwide market.

The BOSS (Bolt On Shaft System) as it is called, basically is a tube that encloses the immersed part of the propeller shaft and combines it with a seal and thrust bearing that is mounted directly on to the hull. The self contained unit eliminates through hull sealing and alignment difficulties, and allows the gearbox and engine to be mounted free of thrust considerations. Between shaft and tube there is oil thereby eliminating shaft corrosion and the necessity of shaft mounted sacrificial anodes. The propeller end of the tube is supported by a P-bracket type of arrangement.

In an unenclosed system a propeller shaft rotating in a fluid creates a force perpendicular to the direction of motion. This is known as the Magnus effect and absorbs energy causing losses: in the BOSS system these losses are not created.

For the boat builder, installation times are substantially reduced and the built-in watertight shaft seal ensures a dry bilge. For the user, the reduced losses give the benefits of lower fuel consumption, improved range or a higher top speed.

It is available for shaft diameters of one to four inches (25 – 102mm) and is claimed to lower propulsion noise and vibration.

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