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Author Topic:   Classic 13: Propeller for 30-HP

j_h_nimrod posted 02-20-2006 12:03 AM ET (US)
I just bought a 1984 commercial hull that has a very unimpressive (read non-existant) hole shot. I know the prop is worn and in need of replacement, so I would like to get the forum's input on what propeller works best with this Honda motor and Boston Whaler hull. I am looking more for load carrying capacity than speed.
jimh posted 02-20-2006 02:13 AM ET (US)
A general solution to find propeller pitch
ESTIMATE TOP SPEED. Using the total weight, the horsepower, and an appropriate hull factor (180 to 200), estimate the top speed of the vessel using Crouch's formula.
PROPELLER SHAFT SPEED. Using the maximum rated engine speed (RPM) and the gear reduction, compute the propeller shaft speed.
PROPELLER CALCULATION. Using the computed shaft speed, the estimated top speed, and a reasonably SLIP factor (for a single propeller use 15-percent), compute the propeller pitch necessary to reach the target speed.
If you supply the appropriate data, I will be glad to show you how to work through these calculations.
j_h_nimrod posted 02-20-2006 02:13 PM ET (US)
Jim, Thanks for the advice. I pulled out the trusty TI-81 calculator and and figured the following.
------------------
I calculated my top speed at 31.6 mph (1200 lb boat and 30 hp)
Shaft RPM comes out at 2885 (6000 RPM with 2.08 reduction)
Calculated pitch came out to 13.7"
------------------
Now I would prefer to pitch down to a 13" for the little extra push. I did a quick search on the internet and found quite a few different options: aluminum or SS, 9 9/10" - 10.5", OEM, Michigan, Solas, etc. I ran a search of this site and there is not much in regards to actual brand and diameter propeller for this boat and motor hp.
What brand and size props have people used with what kind of results?

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Author	Topic: Classic 13: Propeller for 30-HP
j_h_nimrod	posted 02-20-2006 12:03 AM ET (US) I just bought a 1984 commercial hull that has a very unimpressive (read non-existant) hole shot. I know the prop is worn and in need of replacement, so I would like to get the forum's input on what propeller works best with this Honda motor and Boston Whaler hull. I am looking more for load carrying capacity than speed.
jimh	posted 02-20-2006 02:13 AM ET (US) A general solution to find propeller pitch ESTIMATE TOP SPEED. Using the total weight, the horsepower, and an appropriate hull factor (180 to 200), estimate the top speed of the vessel using Crouch's formula. PROPELLER SHAFT SPEED. Using the maximum rated engine speed (RPM) and the gear reduction, compute the propeller shaft speed. PROPELLER CALCULATION. Using the computed shaft speed, the estimated top speed, and a reasonably SLIP factor (for a single propeller use 15-percent), compute the propeller pitch necessary to reach the target speed. If you supply the appropriate data, I will be glad to show you how to work through these calculations.
j_h_nimrod	posted 02-20-2006 02:13 PM ET (US) Jim, Thanks for the advice. I pulled out the trusty TI-81 calculator and and figured the following. ------------------ I calculated my top speed at 31.6 mph (1200 lb boat and 30 hp) Shaft RPM comes out at 2885 (6000 RPM with 2.08 reduction) Calculated pitch came out to 13.7" ------------------ Now I would prefer to pitch down to a 13" for the little extra push. I did a quick search on the internet and found quite a few different options: aluminum or SS, 9 9/10" - 10.5", OEM, Michigan, Solas, etc. I ran a search of this site and there is not much in regards to actual brand and diameter propeller for this boat and motor hp. What brand and size props have people used with what kind of results?