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  #11  
Old 11-21-2012
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Re: Folding prop help

Quote:
Originally Posted by chucklesR View Post
At 15hp your C&C 30 MK1 is already under-powered -
Great Thats the first I'v heard that the 2gm was underpowered plant for the boat. I have been learning a great bit from this site. Thanks for the help. The spring haul-out may just see a new prop.
Thanks again.

Last edited by Faster; 11-21-2012 at 09:53 AM. Reason: fixed quote
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Old 11-21-2012
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Re: Folding prop help

It's not grossly under-powered, but ..

Rule of thumb is 2hp per ton, your boat being 4 tons (8000 pounds displacement) your 15 should be fine - and again BUT -
Your 15 is really less than 10 at normal operating RPM's and and then you have to subtract the transmission loss and if you are lucky you are delivering 8hp to the propeller.
When said propeller is not fully efficient you have a problem.

BTW, the "15" isn't ever real - just like the Universal 25 is really 21hp, the Y15 is really 12hp.
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Old 11-21-2012
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Re: Folding prop help

I recommend you go to YANMAR America Corporation for best advice. C & C designed & built the boat, and would have gone to Yanmar to spec an engine and prop. Fixed props are the norm, folders the compromise to achieve race performance, there is always a trade off - performance under sail v performance under power.

Hopefully you can cut through at Yanmar to someone to get some good, down to earth advise on the BEST PROP FOR YOUR BOAT IN YOUR SITUATION. If you are only cruising you might also consider a 3 blade over a 2 blade.

BTW, our 32 has the offset shaft too. It is great for leaving dock on starboard side as it pulls to port in forward, and great for approaching dock on port side. We dock in a river with canal outflow that varies from 2 to 6 knots throughout the day. We swing a Flexfold geared folder - some minor improvements under sail (well, we finished second in each series this year handicaping against another C&C 32, CS27 & a J24 in main n jib fleet, and it wasn't entirely crew expertise, or was it?), but there is noticable prop whip under power. There are some good SN threads discussing this too.
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Re: Folding prop help

If it's a martec they can tune your prop. Can you get max rpm or are you over pitched? This will effect performance in reverse also.
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Re: Folding prop help

Quote:
Originally Posted by chucklesR View Post
It's not grossly under-powered, but ..

Rule of thumb is 2hp per ton, your boat being 4 tons (8000 pounds displacement) your 15 should be fine - and again BUT -
Your 15 is really less than 10 at normal operating RPM's and and then you have to subtract the transmission loss and if you are lucky you are delivering 8hp to the propeller.
When said propeller is not fully efficient you have a problem.

BTW, the "15" isn't ever real - just like the Universal 25 is really 21hp, the Y15 is really 12hp.
Understood
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Re: Folding prop help

IT,
I have the same power plant a and martec folder, 12x6 I think, on my J28,
7500lbs bare. Forward works fine but the motor/prop vibrate a bit at certain rpms. Reverse is a suggestion, not a command. I get 5.5 knots at 2500rpms in forward. Reverse does hardly anything until it actually starts moving in reverse and the blades open up full. Then it moves fine backward.

It sounds like you props may not be opening properly. Any kind of crud will really effect the prop function. A few times I've noticed "bad behavour" with the prop and a quick dive and clean off straightens it out. Based this being the end of the season and may the problem wasn't noticed early prop crud is my guess.

John
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Re: Folding prop help

Quote:
Originally Posted by jfdubu View Post
IT,
I have the same power plant a and martec folder, 12x6 I think, on my J28,
7500lbs bare. Forward works fine but the motor/prop vibrate a bit at certain rpms. Reverse is a suggestion, not a command. I get 5.5 knots at 2500rpms in forward. Reverse does hardly anything until it actually starts moving in reverse and the blades open up full. Then it moves fine backward.

It sounds like you props may not be opening properly. Any kind of crud will really effect the prop function. A few times I've noticed "bad behavour" with the prop and a quick dive and clean off straightens it out. Based this being the end of the season and may the problem wasn't noticed early prop crud is my guess.

John
Yes, of course i posted this before I read the link.
Now I'm not sure how/if the offset effect the prop effientcy

and yes, I know I can't spell.
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Re: Folding prop help

I have had a 30' sloop with Yanmar 2GM and a Martec folding prop for more than 20 years and have enjoyed consistently good performance from both. Diesels like to work hard; motor at 2600 RPM or more unless prudence requires a slower speed.

The Martec folding prop only works well revved up. Martec claims that their folding prop can bring a sailboat from hull speed to a dead stop in four boat lengths. To test the reverse performance, in open water from a stop run the engine up to 2600 RPM with the transmission in reverse. In twenty seconds you'll be going as fast as you'll ever want to in reverse.

As John noted above, if the prop is gummed up clean it. It won't work well if barnacle encrusted. No prop does. If the prop is worn Martec engineering will refurbish your prop to original specifications refurbish.gif. Martec recommends factory refurbishment every 5 to 10 years depending on, the enviroment that the prop lives in, amount / type of use, size of prop, and number of different operators. I have this done twice and ihave been well please with return on investment.
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Re: Folding prop help

We have the BETA 14 HP on a 35 MARK I and when proped to hit 3600 RPM like it should be there is PLENTY of power
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Old 11-21-2012
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Re: Folding prop help

If you are not going to race, you might consider a three blade.

If it where me, before I went prop shopping I would make sure the engine is putting out the correct RPM. Test it with another tachometer first.

One step at a time....

YMMV.
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