My 1978 Cherubini H30 has a 3 blade 12/10 LH prop. Max speed in calm waters is +/- 5 knots. Of course, my Yanmar is only a 12hp and that may be the real issue. The prop is pitted and cannot be re-conditioned, so I have an opportunity to change the configuration. Because I am racing PHRF, I am considering a 2 blade prop. I would welcome any and all feedback. I have used two online prop calculators and both of them suggest a 3 blade 12/6, which seems like not enough thrust and less top end speed, which is really where I would like to improve.
2 Blade vs. 3 Blade prop and most efficient pitch?
- Thread starter David Popken
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Ernie
Consider the CDI Perfect Pitch Prop
Take a look at the CDI perfect pitch prop for the Yanmar 2GM engine.
Take a look at the CDI perfect pitch prop for the Yanmar 2GM engine.
Don't think that they have a prop for the YSM
Ernie: I do not think that they have a prop for the 1 lunger YSM motors. These engines had a left hand smaller prop. We have a 15" CDI prop on our 2GM and it is great.
Ernie: I do not think that they have a prop for the 1 lunger YSM motors. These engines had a left hand smaller prop. We have a 15" CDI prop on our 2GM and it is great.
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Bill Edmundson
Props
I just did the prop calc at boatdiesel.com. I guessed you have a 2.63 gear ratio. Specs say originally you had a 13x13 2 blade. Prop calc with a total displacement of 11700 can up with 12x13 3 blade cupped prop. max speed 5.4 kts. 2400 rpm cruise of 4.3 kts. You're limited by HP not prop. You can get a 12x13 3 blade LH for $320.00 at glenl.com, under inboard hardware. Good luck, Bill
I just did the prop calc at boatdiesel.com. I guessed you have a 2.63 gear ratio. Specs say originally you had a 13x13 2 blade. Prop calc with a total displacement of 11700 can up with 12x13 3 blade cupped prop. max speed 5.4 kts. 2400 rpm cruise of 4.3 kts. You're limited by HP not prop. You can get a 12x13 3 blade LH for $320.00 at glenl.com, under inboard hardware. Good luck, Bill
Hmmm........
I think I found an archive post last year where someone else was happy with a 13/9 2 blade. I also remember archive posts that confirmed that the 2 blade was original. And there is certainly clearance for 13". Something close to hull speed would be nice.
I think I found an archive post last year where someone else was happy with a 13/9 2 blade. I also remember archive posts that confirmed that the 2 blade was original. And there is certainly clearance for 13". Something close to hull speed would be nice.
Prop Walk?
Also, my 12/10 3 blade prop is horrible in reverse, walking decidedly to starboard with full port helm. How is your 2 blade?
Also, my 12/10 3 blade prop is horrible in reverse, walking decidedly to starboard with full port helm. How is your 2 blade?
Folding prop for racing
The three bladed prop is definitely slowing you down, especially in light winds. Although expensive, a folding or feathering prop will minimize drag while sailing, and will typically provide better power in reverse. Forward boat speed with a well matched prop is a function of engine power, not the number of blades. David Lady Lillie
The three bladed prop is definitely slowing you down, especially in light winds. Although expensive, a folding or feathering prop will minimize drag while sailing, and will typically provide better power in reverse. Forward boat speed with a well matched prop is a function of engine power, not the number of blades. David Lady Lillie
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