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Old 15-10-2019, 04:13   #1
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Aluminium boat in steel filled former shipyard harbour

There's this harbour close to our home. Pretty ideal place in that respect to make it our home dock. It's on the premises of a former shipyard. Deep but with lots of steel in water from 100+ years of shipbuilding. And the water is brackish.

Our boat is a 1993 aluminium in good condition.

Would it be asking for galvanic corrosion to dock our boat here for a season or longer?
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Old 15-10-2019, 06:28   #2
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Re: Aluminium boat in steel filled former shipyard harbour

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Old 15-10-2019, 06:56   #3
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Re: Aluminium boat in steel filled former shipyard harbour

Greetings and welcome aboard the CF, zweeber.

I wouldn't be over-worried about this, but you'll want to gain expertise on the the subject.
The product of aluminum corrosion is aluminum oxide, which is corundum, a very hard naturally occurring substance. When aluminum corrodes, it forms a thin, tight, strongly adherent, transparent coat of aluminum oxide (5000 series alloys are more corrosion resistant than 6000 series alloys). Any damage to this coat is promptly healed by formation of another coat.
Electrolytic (stray current) corrosion & bi-metallic (galvanic) corrosion are relatively easy to prevent, with ample sacrificial anodes, insulation/isolation , and proper wiring with a carefully isolated electrical system.
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Old 15-10-2019, 06:58   #4
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Re: Aluminium boat in steel filled former shipyard harbour

If you have a sound epoxy barrier coat, and hull zincs in good shape - it should not be a big problem.

OFC "it depends" would be the most accurate answer - if are there industrial chemicals in the water along with the steel, or electrical stray current, it could be worse . . . . but a good barrier coat and zincs will protect you from most evils (pretty much everything except incorrect shore power connection).
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Old 15-10-2019, 11:29   #5
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Re: Aluminium boat in steel filled former shipyard harbour

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Originally Posted by GordMay View Post
Greetings and welcome aboard the CF, zweeber.

I wouldn't be over-worried about this, but you'll want to gain expertise on the the subject.
The product of aluminum corrosion is aluminum oxide, which is corundum, a very hard naturally occurring substance. When aluminum corrodes, it forms a thin, tight, strongly adherent, transparent coat of aluminum oxide (5000 series alloys are more corrosion resistant than 6000 series alloys). Any damage to this coat is promptly healed by formation of another coat.
Electrolytic (stray current) corrosion & bi-metallic (galvanic) corrosion are relatively easy to prevent, with ample sacrificial anodes, insulation/isolation , and proper wiring with a carefully isolated electrical system.
Gee, Fe water and Al oxide. Thermite.
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Old 15-10-2019, 12:12   #6
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Re: Aluminium boat in steel filled former shipyard harbour

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Gee, Fe water and Al oxide. Thermite.
Got me, there.
Free heating, anyone?
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Old 15-10-2019, 12:20   #7
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Re: Aluminium boat in steel filled former shipyard harbour

Important safety notice - I don't usually know what I'm talking about!

Having gotten the safety notice out of the way - you asked about galvanic corrosion due to steel being in the water. I seem to recall there are several factors which must all be met for galvanic corrosion - 1) dissimilar metal, 2) must be in the same body of water, 3) the metals must electrically "see" each other (I think that's the way Nigel Calder described it). My guess is that this should not cause galvanic corrosion because you don't meet the 3rd item unless the steel is VERY close to the aluminum. Obviously anodes and epoxy barrier will help - but I'm assuming you are far enough away from steel to break the electrical connection.

Stray current corrosion may be a bigger issue. But that issue can exist in any marina. Nevertheless, I'm following this closely.
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Old 15-10-2019, 12:52   #8
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Re: Aluminium boat in steel filled former shipyard harbour

Thanks so much for the answers. Very clear and helpful. The coating on our boat is good and so are the anodes. It comforting to know that the steel must be close to our aluminium. I guess it’s not. I think we’ll go for it. It’s a nice place. Cheers from a newbie sailor in Amsterdam!
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Old 15-10-2019, 20:31   #9
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Re: Aluminium boat in steel filled former shipyard harbour

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Gee, Fe water and Al oxide. Thermite.

other way round - thermite is aluminium and iron oxide
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Old 16-10-2019, 10:10   #10
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Re: Aluminium boat in steel filled former shipyard harbour

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other way round - thermite is aluminium and iron oxide
I was being a wise guy but stand corrected. Chemistry was 60+ years ago so I turned it around. Rusty water and the aluminum hull?
I feel sure the experts on "electrolysis", as a generic term, will be providing opinions making more sense than me.
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Old 16-10-2019, 19:15   #11
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Re: Aluminium boat in steel filled former shipyard harbour

Decades ago I went for a sail on an alloy hulled boat and when we returned the skipper asked me to help him put it back in the pen, he'd picked me up from of my jerry so I had not seen the boat in it's pen before.

After we'd moored it he reached over both sides and retrieved alligator clips which he clipped onto tabs welded to the deck, the other ends ran to horizontal wires running between the afterward and the forward piles of the mooring. When I asked him what they were for he reached for a wire hanging in the water and pulled it up to show an anode on the end of it. There were about four of them hanging from the horizontal wire on each side of the boat.

I don't know if it worked to protect the underwater hull or if he was just paranoid but it sure looked impressive.
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Old 16-10-2019, 19:28   #12
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Re: Aluminium boat in steel filled former shipyard harbour

You might ask the same question about aluminum boats in Howth, Ireland. The harbor there was set up with iron chains crossing it at regular intervals to hold packet ships in tight spacing in the 19th century. Our compass went in circles when we were moored there. They’re likely to have had aluminum hulls there - contact the Howth Yacht Club: https://www.hyc.ie to ask.
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