lot of effort has been spent in making an engine and also in
measuring the peak power.
is very important that when the boat is out there, cruising, that
the engine revs are at the
revs and deliver the peak power. That the engine and propeller are
the engine is not very powerful then it will only be able to turn
the propeller slowly.
it is very powerful, then the engine will spin the propeller
faster than peak power revs.
way, peak power is not being delivered.
needs to be the correct gearing between the engine shaft and the
only way to find out is to launch the boat and measure the speed.
How? See the next page.
for efficiency, you have fitted the largest propeller that can fit
under the hull.
likelihood is that you will need to reduce the engine revs for the
say peak power is delivered when the engine runs at 500 rpm.
when the engine has reached thermal equilibrium, the revs when
cruising are 400,
change the gearing and re-measure the speed.
changing the gearing until you are definitely over revving.
faster than the revs for peak power
step the gear ratio back one step.
procedure I describe has various advantages.
can all be carried out in the boat. Whilst afloat.
suggestion is that a propeller of same diameter and lesser pitch
Number one. Source the appropriate propeller. Not easy.
two. Either get in the water and fit it under water.
retrieve the boat, fit it and relaunch.
is most likely that the engine shaft is above the propeller
a toothed drive belt between the two accommodates alignment
a small boat, passenger position and weight can flex the hull
alignment of engine and propeller shafts is not easy.
straight line connection between engine and propeller shaft
shaft to be at a steeper angle.
engine likely has a flywheel and this needs to clear the bottom of
propeller shaft has to be tilted to rise up and connect with the
the propeller shaft should be horizontal.
makes this more possible.
to start, equip yourself with three alternative toothed belt
find out how much the revs change between the three settings.
can then work out what number of pulley teeth are likely to enable
you can try a new set and hopefully select the correct ratio.