On Fri, 8 Aug 2003 23:17:49 -0400, "Jim Irvine"
wrote:

Thanks for the clarification and it does sound more like ventilation. I'm
also wondering if trim tab setting can have anything to do with the
condition.

Or, maybe it would be best to stop making this more complicated than it is
and just slow the F___ down when it occurs - Doh!


"noah" wrote in message
.. .
On Fri, 8 Aug 2003 20:28:49 -0400, "Jim Irvine"
wrote:

When cruising with my merc 5.0 alpha 1 on my 22 ft Sea Ray EC, I
occasionally experience what I think is cavitation when encountering
rough
or choppy water at speeds around 35 mph. To get out of this condition,
adjusting the trim has little effect and sometimes it is necessary to
come
off plane. I know there are some devises that can be attached to the
outdrive to help with this. Does anyone have any experience with this
that
could perhaps recommend a solution?

When I refer to cavitation, the condition causes an increase in RPM and a
decrease in speed and is caused by the prop is not making proper contact
with the water, due to too much air around it.



Just so we're all talking about the same thing Jim:

Cavitation is the boiling and condensing of water vapor on the surface
of the prop. Can be very damaging to the prop, as it erodes the prop
metal.

Ventilation is the "sucking" of air into the prop area, causing a loss
of power, and increase in RPM's.

Here's a good "starter" link:
http://www.ribmagazine.com/propellers.htm

If you are ventilating your prop, there are a few remedies:
1.) slow down )
2.) adjust the motor height (down)
3.) try a "doelphin", or similar fin to reduce the induction of air.
4.) probably most important, make sure you have the right prop for
your boat.

Good luck,
noah


Courtesy of Lee Yeaton,
See the boats of rec.boats
www.TheBayGuide.com/rec.boats


Trim might have a small effect, but you'd have to raise the bow, which
is something not usually done in rough water.

If your engine sits "a little high", a doelphin or similar might help
significantly. I use one on my boat, and I get a quicker plane,
better fuel economy, and no noticeable loss of top end. Since they
are larger than the anti-ventilation plate on the leg, they also help
reduce ventilation.

Good luck,
noah

Courtesy of Lee Yeaton,
See the boats of rec.boats
www.TheBayGuide.com/rec.boats