HEre is what you do for cheapest and best speed
Buy the largest diameter suggested
Set a pitch
or if pitch
is fixed order the higher
at top speed you should be able to reach max RPM
and max which means max speed with that prop.
If you can not reach max speed reset to lower pitch or cut diameter of
1/2 to 3/4 inch to lower torque and up RPM
Do not mind the engine
smokes at top RPM.
Now cut down RPM 5-15 percent until engine does not smoke.
Now you have you optimum loading with almost optimum speed
and you have the right cruising RPM
the reason it works like this is : when you reduce the prop rpm the
Hp demand from the prop drops much faster than the Hp capability of the engine
and you have to run at a point where the engine output curve crosses
the prop demand curve to maximise the power train engine to prop
If you size the prop so the engine does not smoke at top engine RPM and then
around at say 90 percent of max engine RPM you hAve reduced the engine output by more or less 10percent but the prop demand (load by
maybe as much as 40 percent) this is just a fact of life a natuarall law if you want go look at two propellers of same dia and pitch one runs at 1500 Rmp
and one at 1350 RPM and you see how much the Hp demand drops.
Then look at a Hp curve for your engine and you will see that the Hp output
at 2700 has hardly dropped anything from 3000 RPM.
You live with the smoke when you must overload the engine going agains hard wind
at top speed and you make it a habit not to use more RPM than just below the smoke RPM. Lower noise
The only other way to beat this is to use a variable pict prop of such a design that you can adjust the pitch while running. This is what you do on a tug or fishing trawler
wher you set the engine speed at best economy probably
80-90 percent of Max engine RPM and then increse the pitch until the engine
starts to smoke and get overload where you cut back a little on the pich
until the engine is ok .Now you are at the point where the props Hp demand
curve inersects the engine output curve