[alberg30] Re: Prop Ghurus assist, please!

[Jack Vanderloo]

From: Jack Vanderloo <jvdloo at cyberus.ca>

Ahoy:
For the record, I'm running a Volvo Penta MD7A (14 SHP) with a 13 x 11
3-bladed prop, and while I have no tach, the old girl happily does 7 knots
in calm water at near full throttle (and 6 - 6.5 knots into any sort of chop
and wind).
Had occasion this summer to run her 12 to 14 hours a day for 6 days -
usually wide open - while transiting the Trent Severn canal system (42
locks, 250 statute miles).  Checked oil daily; used no more than half a
quart at that pace.  Never felt I was stressing the engine.

Did notice, however, at hau-out, that there was a noticeable (1" all round)
"wear" mark in the fibreglass on the rudder (port side) aperture.  Thought
it had been an occasion when the helm must have been thrown, and /or held,
over particularly hard.  Now - as a result of this particular thread -
believe it may have been the result of sustained cavitation of the
LH-turning prop.

Anyone else with this phenomenon?  Comments?

Cheers
Jack Vanderloo
KC 641

"Gordon E. White" wrote:

> From: "Gordon E. White" <gewhite at crosslink.net>
>
> Lee:
>     I think your prop is too big. I have a 21 hp Westerbeke and spin a
> 13 x 11  3-blade. It does not limit me - I can run full RPM of about
> 3,500 if I want (which is trying to push me over hull speed). My only
> problem is at idle it runs about 3 knots which makes for tricky docking.
>
>     Definitely if you can't get rated RPM you have too much prop. Isn't
> a 14 pretty close to the aperture in the rudder? I think you are lugging
> the engine & getting cavitation around the rudder. Not an expert though.
>
>                                         - Gordon White
>
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