Having an engine that runs
perfectly on the workshop bench is very far from having a
Stirling powered boat.
And there is a great variety of types
Each type is different because of the
different circumstances/purpose for the boat.
are two lists. One for the engine to be compatible with the boat –
and the other for
the hull to accommodate the engine
The hull shape must
be long and slim. Stirling engines
are low power. The boat hull
must move through the water with
the least resistance possible. Look at the racing rowing eight
boats. Incredibly long and narrow.
The boat must
Absolutely no trace of a
Canoe or counter sterns let
the water flow cleanly past the end of the boat. Drag is reduced.
A square, flat back end for the boat which reaches down into
the water is hopeless.
Transoms create huge turbulence and
just waste engine power.
A Kort nozzle. Naval architects
have long, long been focussed on how to get the best
out of a boat hull and its engine. We have all seen the bulbous
the front of the supertankers. The
racing sailing yachts rise out of the water on a wing.
kort nozzle is a ring, a very short tube, around the propeller. It
raises boat speeds by
about 10%. It is only works for speeds
under 12 mph. And, being
underwater, no-one sees them or notices them. When you are short
of power, it’s
The propeller must
be as big as possible and rotate as
slowly as possible.
Large slow propellers are the most
be a pressurised Stirling engine.
For many years, there have been many
attempts to power a boat
with atmospheric Stirlings.
There is not enough power from
an atmospheric engine.
The power of the Stirling engine
comes from how many hot molecules of gas are
pushing at the
piston. To get more hot molecules pushing, you can make the
bigger. But then it gets too big for the boat. Have a
look at Brian
Lockwood’s 5 hp
Good horsepower, but too large for a small boat.
To get enough power out of a Stirling, don’t
make it bigger.
Put more molecules of gas in it by
The minimum need is for 2,500 cc of gas at
Or 1,250 cc at 2 atmospheres pressure (i.e. 1
bar = 1 atmosphere above atmospheric)
Or 625 cc at 4
atmospheres (3 bar)
Or 312.5 cc at 8 atmospheres (7
runs at 4 bar.
The engine must
have gearing to the
propeller shaft. Toothed drive belt is the best.
essential that, at cruise speed, the engine is running at peak
With petrol/diesel engines – more revs = more
Not so with the Stirling.
The Stirling develops
most power at a particular rpm rate. (revolutions per minute)
Below that speed heat is
flowing well into the gas. But it could go faster.
speed, the engine is running too fast for enough heat to get into
The faster it runs, the less time there is to heat
the gas. And the power gets less.
“peak power” revs have to be measured on the workshop
Then the gearing to the prop can be set so that the
engine runs at those revs.
be a reverse gear. Reverse gear is
the boat’s braking system.
The epicyclic (sun and
planet) gear box is the only? choice.
be a speed control – The kill
tap (more later) is the best?