Prop, what would you do?

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RichF28
Posts: 16
Joined: Mon Feb 03, 2020 4:33 pm
Location: Charleston SC

Prop, what would you do?

Post by RichF28 »

Looking for opinions, what would you do in this situation... Our boat has a two blade folding Max Prop. the motor is a Yanmar GM20F, about 1100 hrs. The previous owner worked with the company to decide the prop settings. Its a 15" now set at 22 degrees. At cruise we are turning about 2700 rpms, no smoke. If we try to increase revs, it gets to about 2900-3000 but does smoke a bit. The literature I have says that a change of 2 degrees will result in an rpm change of 13-15%. So if I reduce pitch 2 degrees, it should turn about 3000-3100 at cruise, and I assume would have a couple hundred rpms still to go. Do you think it is worth the bother to change pitch next time its out of the water?
The tach has been verified correct, and with no load it will rev up to 3500 rpms.
Freedom 28 sloop Hull #29

RichF28
Posts: 16
Joined: Mon Feb 03, 2020 4:33 pm
Location: Charleston SC

Re: Prop, what would you do?

Post by RichF28 »

Maybe a better question would be, how many rpms are others with a Yanmar 2gm20 turning at normal cruise speed. And do you have anything left if you increase the throttle after that?
Freedom 28 sloop Hull #29

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jamesorr
Posts: 53
Joined: Sun Dec 07, 2008 2:55 pm
Location: Rochester, NY
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Re: Prop, what would you do?

Post by jamesorr »

A bit different setup (i.e. Freedom 32 (Mull), same engine, 3 bladed Max Prop), but I normally cruise around 2800 RPM, which on a clean hull translates to low 6 knots. If in a hurry, I might run at 3000-3100 for a short time period, which moves me into the mid 6's -- so there is that as a data point -- but no observable smoke once the engine is started/warmed up. As the performance goes, has seemed reasonable to me, so I have not looked into tuning it (other then as tuned by the previous owner).
James Orr
Orr What
1988 Freedom 32 (Mull)
Sodus Bay, NY

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JohnReinagel
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Joined: Mon May 08, 2017 1:44 pm
Location: Suburb of Buffalo, N.Y.

Re: Prop, what would you do?

Post by JohnReinagel »

You should be close to max RPS when WOT. If you change prop pitch and get 3400 RPM with no smoke, which you shouldn't, you'll be about as good as can be hoped for.
John


1984 Hoyt F32
Hull #53

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