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Prop Size?
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bobmcd625
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January 22, 2016 - 11:36 am
Member Since: October 7, 2015
Forum Posts: 165
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At the risk of exposing my ignorance, I'd like to know how to determine the correct/optimum size for a prop on a DE38.

My prospective vessel has smoking issues and a friend said it may be a mis match of prop and engine.

This is a DE38 with Volvo 44 hp engine.  The current prop is 16x11 rh.

I understand there is a scientific method for determining this.

Help please.

Frown

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Scott Carle
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January 22, 2016 - 9:32 pm
Member Since: October 10, 2009
Forum Posts: 1480
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This page has stock prop sizes for all boats.
http://downeasteryachts.com/th.....-all-boats

16x11 looks like it is right. I guess you could drop the pitch a little more to see but that is actually at the low end of the stock pitch range.

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Scott Carle DE38 Cutter s/v Valkyr
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bobmcd625
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January 23, 2016 - 12:32 pm
Member Since: October 7, 2015
Forum Posts: 165
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Thanks, Scott.  Do i understand that the prop configuration is determined by the boat rather than the engine?

I would think that a more powerful engine would require a different prop, but maybe not.

Also what is the difference between the R-30 and the S-30?

All the best

BobCool

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Scott Carle
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January 26, 2016 - 9:54 am
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No clue on the difference. R would indicate right hand to me but not sure what S stands for. I would ask a prop shop and then come back and educate the rest of us on it if I were you :) lol

Yes a more powerful engine is going to change that. Most likely with a slightly larger diameter prop or a higher pitch one. You would have to make sure that there is room in the aperture the prop sits in for a larger diameter though. You don't want the tips of the blades coming to close to the hull. I cold see bad things happening even it it didn't actually physically hit. I have played with this on dingys and small boats and the differences in performance can be dramatic. However I did it by trial and error with sub 100 dollar props. I found that the advice of the so called local experts to be less than helpful but if you could actually find someone that knows what they are doing I would lean on them for advice. Trial and error on one of our boats would be really expensive. If the engine is smoking as in working to hard smoking and starting to overheat then I would lower the pitch or drop the diameter a little bit in increments until the engine was happy at max rpm for extended periods of time.

You should be able to have your existing prop modified to a lower pitch. I think if it is bronze they can lower it by a couple points from say 11 to 9 pitch.. or 13 to 11 etc..

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