Nelson Kirsch wrote:

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

If the prop is lifting out of the water in those conditions, you'll want
to lower the motor mount or get a longer shaft, but 20" is already
pretty long.

Cavitation, depending on what exactly you're experiencing, could be
because the prop's not down far enough and surface air is being drawn
in, or possibly that you're simply trying to drive the boat too fast, or
that you have too aggressive a prop. Your engine is nearly as powerful
as ours, you're half our weight and we only use about 5 hp at cruise
power (5.5-5.8 knots, depending on the conditions). If you're trying to
keep to that sort of speed, you might be pushing against hull speed.

As another scenerio: We have an inboard and the prop and engine are just
about perfectly matched to the boat, but we've been stopped twice by
boat wakes or waves and the prop cavitated: Spun in its own air pocket
(or something) and didn't have any real connection to the water. Had to
throttle back for a second to re-establish thrust. Under normal
conditions, we could pull stumps with our 16"x10 3 blade prop (had to,
once), so I doubt there's anything we can do to prevent that.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
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