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Old 02 October 2008, 14:06   #31
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Is the other side the same? because if it's not then how about cavitation?

Pete
It's not, and I hadn't thought of that. No cavitation damage to the the prop though. Would that be evident?
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Old 02 October 2008, 16:57   #32
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It's not, and I hadn't thought of that. No cavitation damage to the the prop though. Would that be evident?
Not sure, I have only had cavitation damage when we bushed a Suzi prop and put it on a Yam engine. Looked right and size was good but just didn't go. However what it did do was strip all the paint off in 10 miles of cruising and pitted the Ali prop quite badly.

If it's not cavitation but only on one side, like the side that the water coming off from the prop would drive towards the annode then perhaps there is something going on there. Afterall the total driving force to make the boat go is through that little shinney whisk thingy at the bottom of the engine.

Other possible thought, you're running a pre mix two stroke, are the exhaust fumes acidic? and the warm water off the prop again pushing against one side of the annode more than the other.

Pete
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Old 02 October 2008, 17:05   #33
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are the exhaust fumes acidic?
they will be.
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Old 02 October 2008, 17:28   #34
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I think it's the wrong side of the anode though for exhaust gases? I wonder if it's connected that both areas of wormholing are right to the edge? I can see how that might tend to support Pete7's cavitation theory.

Martyn, any chance of a pic of yours?
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Old 02 October 2008, 17:38   #35
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I think it's the wrong side of the anode though
Well thats stuffed that theory then

Either way since you still have more than 50% it's not a problem for while yet.

You could always paint it to stop it corroding
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Old 02 October 2008, 17:51   #36
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You could always paint it to stop it corroding
Careful, Timw will do it
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Old 02 October 2008, 17:53   #37
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Well thats stuff that theory then

Either way since you still have more than 50% it's not a problem for while yet.

You could always paint it to stop it corroding
Steady now,.. some peeps will believe you .. If I had to throw a dart in the dart board of answers here .. I'd plump for Jw's answer.. it makes most reasonable sense

No other process can develop such a regular and deep corrosion pattern IMO wierd tho it is
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Old 02 October 2008, 18:02   #38
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Steady now,.. some peeps will believe you .. If I had to throw a dart in the dart board of answers here .. I'd plump for Jw's answer.. it makes most reasonable sense

No other process can develop such a regular and deep corrosion pattern IMO wierd tho it is

I'm leaning that way too.

However....just had a thought-I wonder if it IS caused by oil getting on the anode during flushing as the engine oils up sitting at tickover? It's on the correct side-the side that doesn't get the flushing water thrown onto it by the prop.

Doggypaddle, is your engine premix too?
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Old 02 October 2008, 18:58   #39
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One of the boats i work with has a similar wear on it and i suspect it was caused by cavitation.

The boat was using the wrong sized propellor however thee was no sign of cavitaion burning on it.
The anode had not been adjusted for trim and so it had probably been creating its own cavitation which i believe had caused the same damage as you have on yours.

Is the trim tab offset or left in the centre position?
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Old 02 October 2008, 19:04   #40
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I can't say it isn't but the cavitation damage I've seen looks nothing like that. It's more a fine pitting errosion...kinda like deep sand blasting.
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