What's Wanted for an Engine in a Small Boat?
It should be relatively small. To allow space for people in the boat!
Passengers should be able to see out/round the engine.
Very quiet - even silent. Passengers should be able to talk to each other!
Simple to start. Reliable. Easy to control.
Safe. No dangerous fuels. No explosion risk. No killer exhaust fumes.

Sadly, MANY of the items in the list above are most definitely NOT available in many small boats.

The Stirling engine does meet many of the requirements.
Interestingly, regarding the size of the engine, the Stirling engine size can be adjusted as required. The size of the engine can be halved if the interior pressure is doubled. What matters is the number of gas molecules inside the engine. By doubling the pressure the number of molecules pushing at the piston is doubled. The engine power is doubled. A pressure of 15 psi doubles the power. 30 psi triples the power.

During the various Stirling boat rallies, various engine control methods have been trialled.
Reverse gear and speed control are easily achieved. Sadly, small boats often lack reverse gear.

These Philips engineers, back in the 1970's?, had worked it all out.
Look at the low profile engine in the small box!

Petrol is extremely explosive. Most small boats are hand fuelled with petrol.
An LPG cylinder, used to heat a Stirling, does need standard Boat Safety certification. Sealed, refillable LPG cylinders are far better than hand poured petrol tanks.
The crucial certification of a steam boiler is not involved.

The Stirling engine can meet the needs for a small boat and also deliver a "better" boating experience. .......BACK