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Ericson 27/ Yanmar 2gm prop size

Hi, I'm looking to replace our exisiting 3 blade prop with a 2 blade. I think the 3 blade is too small as the boat barely powers at 4 3/4 knots. No tachometer on the boat though. Anyone have this boat and 2 cylinder diesel with a gear ratio of 2.62? Is hull speed about 5.5 knots?

Thanks, David
 

Glyn Judson

Moderator
Moderator
Prop size question.

David, Thanks for including the ratio of your transmission 2'62:1, that's a big factor in choosing prop size. It might be of interest to know that your same engine in an E31 hull #19 has a 3-blade, 13 X 12 X 1 prop and is able to achieve hull speed of somewhere in the range of around 6.5 knots or better. Please check your prop numbers first and let the list know so we can make more accurate recommendations. Unless you can't live without a 2-blade, I'd highly suggest working with your present one first because with a little tweaking, you might end up just fine. As an example of how little a change makes, I have the Yanmar 3GMF and achieve the same speeds as hull #19 with a 3-blade 13 X 12 1/2 X 1. Of course these as with yours are right hand props. Curiously, my Kanzaki KM3P transmission reads 2.61:1. Do you have the same transmission or is is different for the 2-cylinder engine and therefore a 2.62:1 instead? Glyn Judson, E31 hull #55, Marina del Rey, CA
 
Glyn, My diver hasn't been able to get the present prop off yet so I don't have any numbers other than hull speed plus it looked smallish last haul-out (tons of room 60% ?). I like sailing better than motoring, so hope to feather a new 2 blader on center and sail a bit faster/higher. The box is a Kanzaki KBW10 2.62 ratio. Motors a 2gmf Yanmar.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Either a two or a three blade fixed prop will drive your boat at hull speed, IF the prop has the right pitch. Sounds like your present prop is not the right one for your boat. (Presuming that you are hitting normal speed under sail, so we can deduce that the hull is not slow due to fouling.)

Loren
 
We can deduce a few things. That's right!

A few sites suggest the 15x11 x 3/4" propeller for the 2gmf. I wonder if it'll swing. Off to the marine exchange in Seattle (our fine city).
 
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