Hello Nelson,

First let's get the correct terminology. What you most likely have is prop
ventilation, where surface or exhaust gas enters the prop stream and reduces
the thrust. Cavitation is the boiling of water on the low pressure side of
a prop under very high thrust conditions, often damaging the prop. This
doesn't happen on low hp motors.

see:
http://www.powerboat-training.co.uk/...rs-ventilation
,%20cavitation.htm

Look for a way to get the motor lower in the water, usually by moving its
bracket, assuming its tiller still has room above the transom. Otherwise
you need a longer shaft. Normally the motor is best set for zero
tilt....prop shaft horizontal.

Brent
www.bensonsails.com



From: Nelson Kirsch
Organization: AT&T Worldnet
Newsgroups: rec.boats.cruising
Date: Thu, 04 Sep 2003 13:08:39 GMT
Subject: Cavitation

Greetings,

I've a 22' D&M sailboat. It weighs in at 4000 lbs with 2000 lbs of
ballast. Right now, I have a Johnson 15hp motor with a 20inch shaft on
the transom. The boat floats pretty much on its lines.

I'm experiencing a lot of cavitation when underway in moderate seas (2-4
ft) and am wondering if this is standard for an outboard powered
sailboat or if perhaps I need a longer engine shaft. Also, would
moving the tilt pin forward or backward help?

Any thoughts or comments would be greatly appreciated.

Thanks,
Nelson