Need Help with Prop Size

[ironworker]

need help sizeing a prop for the sailboat im building.Its a hanna carol ketch ive got a volvopenta 36hp md17d with a 2.38;1 trans in her ive contacted 2 prop guys about this one says 20 dia. 11 pitch the other one says 18 dia 12 pitch the boat weights 15 tons with waterline of 32ft i cant get 15percent hull clearence with the larger prop.ive got 1 3/8 clearence between tip of blade top and bottom if i go with 20dia.the boat is a double ender so the hull around the prop is1/2 thick do you think that would cause problems. the rpms on the motor go up to 3000 would like to have the biggest prop possible thanks for any advice yall could give me smooth sailing to ya will join yall soon ironworker.

[ovrmyhead]

Google michigan prop. They have an online form you can fill out and they'll get back to you in a few days with a prop recomendation.
Those seem like big props. I have a 32' waterline, 11k boat, 29hp perkins with a 2.01 to 1 hurth. They recomended a 15X9 three blade. The prop I just broke I found was a 17X9 and I could never get it even close to cruising rpm.

[Bash]

Contact any prop shop. Making this sort of estimation is what they do for a living.

[djmarchand]

Contact Larry at Accutech in New Hampshire. Go to www.accutechmarine.com or email larry@accutech.com. Larry is a pro and will sell you a prop that will work right.

New Hampshire may be a long way from you, but shipping is relatively cheap.


David

[donradcliffe]

Try this calculator--I came up with 18x13--http://www.castlemarine.co.uk/pitch.htm