Prop Rot

[DickB]

Yee gods, After scrubbing all the garbage off my aluminium prop I notice some pitting in the blades. The question is, how much can I get away with? In the middle of the blade there are a couple of patches about 5 - 8mm across and a couple of mm deep. It is a 17 x 12 prop off an MD22 saildrive... (about 5 years old)

Any views... Do I risk putting it back or fork out 200 for a new one? (or better still fork out loads of cash for an Autoprop!!!!)

<hr width=100% size=1>Dick

 

[Avocet]

I guess it's de-zincification. Mine has similar signs although there are more of them and they're each not as deep. Has it gone copper-coloured in the pitted areas? I'm told the solution is to fit a sacrificial anode to the propshaft but I can't easily do it on mine. Daren't say how long you've got but there's a brilliant photo in this month's PBO (p.101) Looking at that, I'd guess I've got another 150 years before mine needs changing!

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[DickB]

Thanks for that, I'll check it out. I have this vision of a great chunk of blade breaking off but I tihnk I can risk it a little longer. The reason is the Anode failed...

Now fixed anode but left with some rot on the blades...

<hr width=100% size=1>Dick

 

[ex-Gladys]

...aluminium prop won't de-zinc....

<hr width=100% size=1>Larry Botheras

Anderson 26 "Amber"

 

[oldharry]

... no but it can still be eaten out by galvanic corrosion. Wrong term for right result!

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[dickh]

Is the anode on the prop corroded away? Don't know where the anode is on a Volvo though.............


<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[DickB]

Yep... The anode is just behind the leg of the saildrive. It was so corrroded that it rattled around on the retaining screws. My guess is that is when the rot occured. The thing is, do I replace or chance it? Some deep pitting on the blade face is evident. Will the blade break?

<hr width=100% size=1>Dick

 

[Talon]

That was our worry with the first set of props, so we brought new ones, the damage a prop blade breaking off could potentially do is something I never want to find out.

What Volvo legs do you have?

<hr width=100% size=1>Alex

<A target="_blank" HREF=http://www.mad-als.com>http://www.mad-als.com</A>

 

[BrendanChandler]

Perhaps you need to find the electricity leak first and fix that.

The anode on my hull is about 50% used after about 6 years.

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http://hometown.aol.co.uk/brendanchandler/index.html

 

[TheBoatman]

Dick
You need to make sure that the boat is wired up to prevent electrolitic action. Any dis-similar metals in salt water will cause you problems.
Wire everything together, sea cocks, engine, etc. and conect them to a decent anode.

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[DickB]

Thanks for all the help and advice. I will probably get another prop, just to be on the safe side... (and fix the anode issue

<hr width=100% size=1>Dick

 

[Avocet]

I apologise for being a complete wassock! - didn't read your post properly! As has been said, only alloys with Zinc in them can suffer from dezincification!

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[DickB]

I am fitting a galvanic isolator and new anodes , but I am still left with the dilemma of whether to buy a new prop (200+pounds) or put the old one back with a bit of rot on the blades. I just don't know what would be considered serious rot...

I have got a couple of months to chew this over but I suspect I will go and buy a new one!!!

<hr width=100% size=1>Dick