New Prop Question

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DennisMansour

DennisMansour

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Apr 20, 2009
31
Hunter 34 St.Margaret's Bay, Nova Scotia
Good Day,
Head South this July from Nova Scotia for at least a year and I am told that making a slow trip along the USA coast and the ICW is 95% motoring. I have the origional Prop. 15in. with a 15 pitch, 2 blade fixed, 1in. shaft. I have a good local Foundry to supply the new one. Want a 16 or 17 in. with the same 15 pitch and fixed.
Not interested in spending nearly $3,000.00 on a folding prop.
My question: is a 16in. or a 17in. Prop both do-able with my existing 1985, 34ft. Hunter, Yanmar and Tranmission?
Many thanks.
Dennis
 
Richard Bryer

Richard Bryer

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Jun 3, 2004
890
Hunter 34 Toronto, Ontario Canada
I would say you will be over propped- ie you will not be able to run at high enough rpm because you will be at hull speed. I would also worry about cavitation caused by insufficient hull to blade tip clearance.

I went from a two blade 15X12 to a 3 blade ( CS) 14X9 and it was too much. Had to drop to 14X7.
 
S

Steve Dion

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Dec 2, 1999
15,184
Hunter Vision-36 Rio Vista, CA.
The issue is the tip clearance. I believe that the "Pro's" (whoever that may be) recommend no less than 15% of the prop diameter for tip clearance.

If I was purchasing a new prop for your boat I would definetly look at the Campbell Sailor. Let them do the sizing for you. Norm is a great guy and may already have the specs for your boat.

http://www.westbynorth.com/CampbellSailer.aspx

I have seen a couple of boats that have switched to one of these props and it has made a marked difference the the motoring performance. The other thing is they are much more robust in their construction. If you hit something with one of these props it has a much better chance of surviving with little or no damage.

It will also not break the bank.
 
N

navigator97

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May 24, 2004
470
Hunter 33.5 Portsmouth, RI
Dennis, We have a 1990 Hunter 33.5 (Close to your size Hunter) with a Yanmar 2GM20F engine. I had a 16" x 11" 2 blade prop on a 1.000" shaft. After putting in new injectors the diesel mechanic (a VERY good one) did a "test drive" and said it seemed that it was over propped. I couldn't go over 2900 RPM with out getting black smoke. I had a local prop shop cut it down to 15" x 11" size. After re-installing it I can go over 3000 RPM and still get the speed I had before. Much better performance. I would think the 16' or 17" is too much diameter and that 15" pitch is certainly too mush. The previous advice of talking to a good prop shop and have them calculate the appropriate diameter and pitch is good advice. Good luck.
 
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