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Topic: cavitation

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gecherm
Forum Member

Joined: 04 June 2007
Posts: 16

Posted: 04 November 2009 at 4:04pm \| IP Logged

I have a 23 foot W/A and recently noticed cavitation only when turning right at 3k or more. I have my transducer placed on the right and it is a few inches higher than the top right hand side of the prop blades. I am wondering if the transducer is causing it or is it possible to be related to the drive. I have a mercruiser 350 with alpha gen II drive.

jehines3
Forum Member

Joined: 19 May 2003
Location: St. Michaels, Maryland, USA
Posts: 1283

Posted: 05 November 2009 at 8:43am \| IP Logged

Its likely related to prop direction. Trim the drive down a bit before making turns to get a deeper bite. maybe take some trim tab out to squat the boat too.

__________________
John E. Hines III, P.E.
1992 Silverton 34ACMY
Twin Crusader 454XL/Borg Warner 5000

SwampNut
Forum Member

Joined: 08 February 2006
Location: Chandler, AZ
Posts: 3843

Posted: 05 November 2009 at 12:04pm \| IP Logged

First off, sounds like you're describing ventilation, not cavitation. Does the prop show pockmarks or damage like it was sandblasted? If not, then it's ventilation.

The transducer is much closer than recommended. I suspect that's at the heart of the problem. Also, is your anti-ventilation plate intact? Do you have any add-ons like a fin?

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2001 Bayliner Ciera 2455
5.7 Bravo III

gecherm
Forum Member

Joined: 04 June 2007
Posts: 16

Posted: 05 November 2009 at 1:01pm \| IP Logged

swampnut,

I have pitting on the prop but that is usual for a season. My anti-ventilation plate is intact and I don't have a hydrofoil. What happens is the same as hitting weeds. Not enough water on the blade surfaces. It will only do it while turning right. slight turns does not do it either. I suspect the transducer because it is close to it and on the right. I will try and drive it next year with the transducer up and see if it happens but wanted to know if there is any idea that there could be something wrong with the drive. I would gather that it should be doing it in right and left turns if it was. I have the boat in the yard now and was looking for advice, or things to look for. I can't really locate the transducer anywhere else as the transom has trim tabs and the hull has ribs. If I go further up the transom I will be either too close to the trim tabs or in front of a rib. The transducer did have some growth on it but no more than usual.

SwampNut
Forum Member

Joined: 08 February 2006
Location: Chandler, AZ
Posts: 3843

Posted: 06 November 2009 at 10:18am \| IP Logged

A ventilation problem would be anything hidden in the drive; it would be visible damage. Cavitation can be caused by prop damage, incorrect prop, or improper drive positioning on the boat (manufacturing error, unlikely). Cavitation causes a lot of prop damage in the form of pits on the surface and edge erosion. Ventilation does not, it's just annoying.

__________________

2001 Bayliner Ciera 2455
5.7 Bravo III

jehines3
Forum Member

Joined: 19 May 2003
Location: St. Michaels, Maryland, USA
Posts: 1283

Posted: 06 November 2009 at 11:14am \| IP Logged

The transducer on the downward side of prop swing could be causing ventilation depending on how close you mean by close. To determine for sure piviot it up out of the way in the trailer position and try a run with it. I think it is more an issue of Left side lift during a right turn causing the high side blade to thrash air.

Just my opinion and worth what U paid...

But really any high speed turns on a single engine boat are always differing side to side. Even on twins the high side engine will pick up a little and the low side engine will dig in a little, thus creating a tach mismatch.

You could try a foil if you determine the transducer to be the culprit rather than relocate.

__________________
John E. Hines III, P.E.
1992 Silverton 34ACMY
Twin Crusader 454XL/Borg Warner 5000

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