Page 32Shaft Seal


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So far, this book has been largely about maximising the power output of the engine.

There are two other major concerns.
Not losing, or wasting power anywhere between the engine and the propeller.

Choosing a hull shape that slides through the water as easily as possible.

The first place engine power can be lost, is the point where the shaft exits the crankcase.

A pressurised engine needs a seal between the rotating shaft and the crankcase wall to
retain the helium gas.

Rotating shaft seals are nothing new to the engineering world.
Unfortunately the “off the shelf” units are for the world of far higher power levels
and they can accommodate far higher levels of friction.


Rather like the piston ring, the Stirling engineer needs something with lighter friction.

The result is shown opposite

An “O” ring is pinched between the shaft and a cone shaped housing by a screw cap.

The holder (purple) for the shaft Oring has another O ring. This static O ring prevents leakage through the screw thread between the purple piece and the pink housing.

The degree of grip (friction) can be adjusted to just the level needed.