Which propeller

[Craig Cape Town]

Please help determine the size and pitch of a 2 blade propeller for my dufour 2800.

http://sailboatdata.com/viewrecord.asp?class_id=694

I'm replacing a volvo MD7 12hp (spins left) with a yanmar 2QM15 (spins right). The old prop is a long flat blade type and the props for sale now are a different shape (more rounded).
The yanmar is a 14 hp with a 2.14 gear ratio.
The sailboat LOA 27.08 ft, LWL 22.14 ft, draft 4.8 ft, displacement 6064 lbs.

Does the new prop have to be exactly the right size or is there room for a little difference?
Thanks

[DougR]

My program says a 16 X 9 x2 should do the trick, or a 15 x10 X 2 , with the 16" slightly more efficient. However you should chose the prop which allows you to have between 10 and 15% of the prop diameter for tip clearance....

So for the 16" prop you want to keep at least 1.5" between the blade tip and the hull, and the more the better. If the prop tip is too close you can get noise and vibration.

DougR

[Craig Cape Town]

Thanks Doug.
A mate has a 13 inch with a 10 pitch which I could use. How much difference would the slightly smaller diameter make?

[DougR]

Try to stay with the 16" if you can....
The 16" prop will have about 30 to 35% more blade area than the 13" prop so will be able to push much better at high throttle settings, into chop, etc.

You can try the 13", of course, but I think it will have thrust breakdown and cavitation at high RPM.

DougR

[Craig Cape Town]

Thank you

[Overlord]

I might have one for you. I’ll be back in Cape Town on the 28th of this month.
Pm me your number and I’ll call you.

[Craig Cape Town]

Thank you guys. I've been told to use a 14 x 9 or 15 x 9. I have a 13 x 10 in hand and I'll give thst a go .