Westerbeke 18hp Prop Size

[redfishnc]

Am about to complete purchase on a CP-27 with an 18hp engine and am wondering what prop most owners use?  The previous owner has an 14x10 three blade currently installed and I don't remember what prop he replaced.  What prop do you use with this engine and the Hurst reduction gearset?  thanks

[Allure2sail]

Hi:
Not really the answer your looking for but the m-12's have a 12" X 8 degree prop. My salvage boat oddly enough had a 12: X 9 degree prop. Never could figure that one out but I don't think one degree is a big deal. The pitch sounds about right and I understand that a 3 blade can be slightly bigger than the two blade it replaced but I'm not one to give you a definitive answer on it. I do know that with the M-12 the boat is underpowered. I will follow your thread because I'm curious as well. Good luck with the purchase.
Bruce

[skip1930]

Com-Pac probably purchased ANY prop that was close to being right.
Who's to say what is correct for such and such a boat.

A three blade is fine. A two blade is fine, but has more pitch?
Both move about the same amount of water?

Can the engine come to the maximum running speed?
Over speed? Change something, pitch or dia, move more water.
Can't come to speed, find less prop. Move less water.

I don't think I'd want to run a diesel at or near max rpm.
Slow and steady. Lower that RPM w/o lugging her down.

Dad had twin Chrysler 383's into Velvet Drives and they spun up 5 blade props. On a hull plane this house boat maxed out at 24 knots with both Carter 4 barrel's wide open, the churns would only turn 3,100 rpm's max. I don't think they could go any faster without caveatting.

skip.

[BobK]

Any inboard engine that has the proper sized propeller on it should just reach maximum RPM.  A good rule of thumb is 1" change in either pitch or diameter should change the RPM by 200 RPM either up or down.  I would aim for 100-200 RPM less than wide open throttle on a diesel since they are governed at max RPM.