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Old 26-03-2010, 21:17   #1
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What's the Gray Aluminium-Like Coating on My Prop ?

I can't seem to solve this despite asking many people.
The 10 year old coating makes the bronze prop look like its made of aluminium.... actually, I thought it was aluminium until I tried to make it smoother with a polisher and cutting paste... I then discovered that it was only a coating.
My boat is aluminium, so maybe this was done on purpose.
The coating is conductive and does not easily come off.... the wire brush on the angle grinder has no chance for example. It is a seriously hard, well stuck on coating.
So now I have the prop with a bit of polished bronze showing through which is a problem as the antifoul does not stick here well.

I am now so impressed that I would like to put this coating back.

Any ideas anyone ?
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Old 26-03-2010, 21:45   #2
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What's the Gray Aluminum-Like Coating on My Prop ?
Probably anti fouling coating made for props. I doubt it is very old. The stuff wears off and they charge a lot to apply it. Using ordinary anti fouling paint lasts about a week and the good stuff about 9 months.
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Old 27-03-2010, 08:22   #3
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Hi John,

I think you're looking at an aluminium coating on your bronze prop. After 10 years you reach the end of life of those.

The only places (in Holland) that I know do these coatings are for commercial ships like river barges. They apply it to steel primarily. I think the application is much like sand blasting, fusing the aluminium on the targeted surface.

The aluminium disappears slowly because it is less noble. This is the principle of it's protection, much like galvanized (= zinc) steel.

I would give some commercial prop-shops a call to inquire about a new finish if you like it.

ciao!
Nick.
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Old 27-03-2010, 10:20   #4
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Hi Nick,
My aluminium boat was actually built up by the North Sea.
The aluminium had not shown any signs of disappearing, the only reason I found out that the prop was bronze is when i tried very hard to polish it and so saw the bronze under the surface coating.

I know that the general view on these forums is that nothing sticks for long to a bronze prop.... but I have living proof that its not true. (the prop was 10 years old)

I love it because the prop antifouling sticks so well.... I should never have tried to improve something that did not need improving.

Would you have any idea of how I could find one of these companys in Holland as i really regret having tried to polish it. Or would you know the term to use so i could google it.?

thanks again
John
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Old 27-03-2010, 12:28   #5
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This may be it.

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Old 27-03-2010, 15:25   #6
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Hi John,

I tried to Google for more info but failed. I don't understand it because it was introduced with lots of press about 20 years ago... but there's not much info about this on the web anyway.

ciao!
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Old 27-03-2010, 15:50   #7
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prop coating

Perhaps it was flame sprayed aluminum? Flame sprayed coating services including high and low velocity sprayed coatings - Flame Spray Coating Company, Detroit, Michigan

It's a fairly common industrial process... before the advent of modern epoxys flame spraying zinc or aluminum was all the rage for steel boats.

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Old 28-03-2010, 02:11   #8
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Aluminium filled vinyl primer?

My guess is that it's some sort of aluminium filled vinyl primer. International Paints sell one under the name Primocon.

If you look very carefully you may be able to see a very thin layer of red etch primer on the bronze, under the aluminium stuff.
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Old 29-03-2010, 08:53   #9
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Originally Posted by bob kingsland View Post
Perhaps it was flame sprayed aluminum? Flame sprayed coating services including high and low velocity sprayed coatings - Flame Spray Coating Company, Detroit, Michigan

It's a fairly common industrial process... before the advent of modern epoxys flame spraying zinc or aluminum was all the rage for steel boats.

Best, Bob S/V Restless
And.... the price for finding the info goes to Bob!! ;-) This is exactly what I mean and what I believe is on the prop. No "paint" system will last 10 years on a prop I think... even with a 3-step etch primer system it didn't last 3 years on Jedi...

ciao!
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Old 04-04-2010, 15:57   #10
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I guess that's what was on my prop as well. When I purchased my used boat 2 years ago, small areas of the coating had worn off. It was very difficult to remove the remaining stuff. In any event, the original coating did not repel banacles....so I'm not use of its' purpose.
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