The Stirling engine is rather
too tall for a boat.
The pumped beta diagram is
something like 5 times
taller than it is wide.
Boats need a low profile, low
centre of gravity engine.
The lever elbow linkage
shortens the engine by “bending” the con rods through
displacer rod is connected
to the end of a lever. This means that the big end of the
rod traces out an arc. The longer the lever, which is near
horizontal, the gentler the arc. This reduces side forces and
The centre of an “elbow” is
pivoted at the mid point of the lever.
One end of the elbow
is fixed to the pin
on the crank disc.
The piston con rod is connected to
the other end of the elbow.
When the piston is pushed
by the gas, the con rod swings the elbow and, in turn,
pushes on the crank disc pin and turns the shaft.
is horrendous to describe.
Have a look at an animation
Why bother with this linkage?
shortens the height of the engine whilst preserving near straight
line motion of the con rods.
There are absolutely
perfectly straight line linkages. (No side forces)
1960’s rhombic drive is rightly world famous.
keeps the engine tall. (And takes some skill to make)
lever elbow linkage is just levers – much simpler.