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Old 15-04-2011, 15:42   #1
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Propeller Size and Pitch for Yanmar Saildrive

Am ordering 2 new 3-blade fixed props for my Privilege 37 (1996). Yanmar 3GM30s with SD20 saildrives. Don't recall the size and pitch of the existing props, which have worked OK, and I need to submit the order before she's pulled out of the water and I can actually look at the existing props. The information available on the internet is inconsistent. Some charts say use 16 x 11. Some say 16 x 12. Does anyone out there know?? Regardless of the existing props, if there's room for improvement, I'm all for it.
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Old 15-04-2011, 16:05   #2
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Re: Propeller Size and Pitch for Yanmar Saildrive

Have you tried Michigan wheel's website? They used to have an input form to calculate a prop size for you.
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Old 15-04-2011, 21:15   #3
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Re: Propeller Size and Pitch for Yanmar Saildrive

Good luck. Most (if not all) calculators are for single props.
Went thru this process several years ago when I repowered my Privilege P43. Replaced 3 cyl 38hp Yanmars with 4 cyl 56hp. I have straight shafts (not sail drives) and ended up with 3 blade 16D x 10P, which puts me within 50 rpm of WOT under load. (Prop manufacturer recommended 14x12 which left me 300 engine RPM short of max RPM (3800) at WOT. Your local prop shop might be a better source than mfr. (As a point of reference, my Privilege is 47ft waterline, about 30,000 lbs displacement and cruises between 10 and 12 knots at 3400 engine rpm.)
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Old 16-04-2011, 04:49   #4
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Re: Propeller Size and Pitch for Yanmar Saildrive

Greetings and welcome aboard the CF, CatamaranDan.
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Old 16-04-2011, 05:10   #5
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Re: Propeller Size and Pitch for Yanmar Saildrive

Quote:
Your local prop shop might be a better source than mfr.
Talking to a good shop is really the best way to go. Propeller science is quite refined. Based on engine, transmission, and hull there is a correct prop that can be computed to get you full rpms at max throttle (or close to it). That is always the goal to determine the optimal prop size and pitch. Hulls do vary but I wouldn't just guess or totally rely on a web site alone.
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Old 16-04-2011, 06:39   #6
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Re: Propeller Size and Pitch for Yanmar Saildrive

Is it possible to contact the manufacturer to see what was on the boat?
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Old 09-07-2012, 08:15   #7
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Re: Propeller Size and Pitch for Yanmar Saildrive

Hello Catamaran Dan

I also have the same engines and saildrives (Yanmar 3GM30FC and SD20) on my Admiral 38 Cat and am looking at replacing my fixed 3 blade props for folding props. Did you find out any more info on the correct prop size? I've look at a couple of different prop suppliers and the recommendations seem to vary between 16" and 17" depending on the props.

The manual I have for the SD20 only refers to the 3YM30 Engines (and says max prop size = 16" for folding. 16.5" inches for fixed.

Any info you found would be appreciated, thanks
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