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Old 16-01-2021, 07:05   #1
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42’ Aluminum Ketch

I have a few questions regarding Epoxy products and bottom paints for an Aluminum Sailboat.

I have a 42’ aluminum ketch that I have begun restoring. I am not positive on the alloy but I know it is 5-6k marine grade. The hull was built as a shell, flipped over and the keel with iron ballast welded on.
So they are separated without access and a void area in most the keel.

I am removing most of the keel plating, framing, and rebuilding it currently. due to some thin areas and corrosion around the iron ballast. The hull itself is in near perfect condition with little to no corrosion signs.

Additional zincs will be added on and the keel will be practically all new plate.

Specially below the waterline, I believe the best option is to sand down to bare aluminum, acid wash, dry, and apply a barrier coat of epoxy. Then a zinc based paint/anti fouling. Is this correct? I would like to put quite a few coats. any product recommendations or advice?

Thank you for your time
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Old 23-01-2021, 22:21   #2
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Re: 42’ Aluminum Ketch

Bump.
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Old 23-01-2021, 23:25   #3
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Re: 42’ Aluminum Ketch

Hehehe, maybe you did not get a response because most readers did not know what a good or best way for an alloy boat is.
I must say, neither do I, ask me about steel, ferro or GRP. The alloy boats I use were/are rescue boats that come out of the water on a jinker after use, and they remain bare bottom.

I am not sure about sanding, I know for the topsides best is sandblasting to a specific grain (hmm, there must be a better word for the 'undulations') to optimise adhesion.

Maybe this link gives some info, although not very detailed: https://www.misterantifoul.com.au/bl...to-your-vessel

Good luck in your hull preparation. Last point, do not put ordinary zinc anodes on an alloy hull. There is a grade/type that is specific for aluminium.
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Old 24-01-2021, 10:39   #4
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Re: 42’ Aluminum Ketch

Usually it’s sand blast then quickly coat with etching primer
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Old 29-01-2021, 00:03   #5
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Re: 42’ Aluminum Ketch

Thank you for the advice.

Turns out the keel is lead and not iron like the schematic says. The keel plating has been cut out and new frames, cross members, and plating will be welding in the coming days. I decided to epoxy barrier coat the interior and exterior keel. Most importantly coating the lead and aluminum to prevent dissimilar metal contact. All of the corrosion I found was in this area.

I have a few questions.

Anodes- aluminum or zinc? Best method to attach? I was think to weld aluminum studs and use nylon nuts to fasten.

Bottom paint? What is best for an aluminum hull?

Any suggestions on an etching acid for aluminum to use prior to any coating?

Thank you in advance
Tyler
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Old 29-01-2021, 00:13   #6
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Re: 42’ Aluminum Ketch

Quote:
Originally Posted by Thumperfish View Post
Thank you for the advice.

Turns out the keel is lead and not iron like the schematic says. The keel plating has been cut out and new frames, cross members, and plating will be welding in the coming days. I decided to epoxy barrier coat the interior and exterior keel. Most importantly coating the lead and aluminum to prevent dissimilar metal contact. All of the corrosion I found was in this area.

I have a few questions.

Anodes- aluminum or zinc? Best method to attach? I was think to weld aluminum studs and use nylon nuts to fasten.

Bottom paint? What is best for an aluminum hull?

Any suggestions on an etching acid for aluminum to use prior to any coating?

Thank you in advance
Tyler
Cant offer any advice except that NO copper in the antifoul, and two pack etch rather than the single pack..
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