Despite the reality expressed in another quote:
>And all that produces the rule-of-thumb: get the lowest pitch prop
>available for your engine. Nobody wants to go slower than us!
it occurs to me that someone may ask: determine how?
Here's how I'd do it, using a knotmeter and engine tachometer:
1) Decide upon the speed at which you'd like to have max power available
(I think I'd choose that hull speed be reached at maximum engine rpm,
_if_ the hp available at max rpm is sufficient to move the boat at near
hull speed in flat water & low wnd. Max hp would then be available at
something a bit less than hull speed.)
(desired speed) = (max speed) x {(rpm for max hp)/(max rpm)}
2) Measure boat speed with engine at (rpm for max hp) rpm. Call it
(actual speed)
3) Calculate desired pitch, based on actual pitch:
r = [{(desired speed) - (actual speed)}/(actual speed)]
(desired pitch) = (actual pitch) (1+r)
Now, if your prop is metal, Joe's Prop Shop may be able to modify it by
brute force to the desired pitch. If it's a plastic prop, I don't know if
mods are possible, but I doubt it. Anybody know?
SInce my husband-in-law has a ski boat, I was once exposed to the
mythology of props. That taught me to not take any of it too seriously
beyond the basic (idealized) science as herein.
Regards,
Bill Combs
WWP 19 #439 (August 1987)
"Ursa Minor"
Fort Walton Beach FL
ttursine@gnt.net