Aluminium boat in steel filled former shipyard harbour

[zweeber]

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?

[flyingnut40]

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[GordMay]

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.

[Breaking Waves]

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).

[Cadence]

Originally Posted by GordMay

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.

[GordMay]

Originally Posted by Cadence

Gee, Fe water and Al oxide. Thermite.

Got me, there.
Free heating, anyone?

[Pelican_38]

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.

[zweeber]

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!

[mickt243]

Originally Posted by Cadence

Gee, Fe water and Al oxide. Thermite.

other way round - thermite is aluminium and iron oxide

[Cadence]

Originally Posted by mickt243

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.

[RaymondR]

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.

[psk125]

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.

[thaisail]

What material is recommended for aluminium hull anodes used exclusively in salt water?

[thaisail]

I have been using Vetus zink anodes since 1982 on my 36 foot aluminum sloop and they almost never corrode. The anodes are isolated from the hull with the internal stainless bar in the center of the zinc anode bolted to an aluminum doubler plate that has threads cut into the doubler plate. There are 4 anodes bolted to the hull and there is an epoxy paint barrier between the zinc anode and the doubler plate allowed the electrical contact to pass only between the stainless bar embedded in the anode which is threaded into the aluminum doubler plate with aluminum female threads using 316 stainless bolts.

I have heard that the anodes should be made of an aluminum alloy now to better protect the hull and some say that the aluminum anodes should be bonded to the bare aluminum doubler plates. Anyone out there with experience with these new aluminum alloy anodes, please pass on your experience.

[smac999]

Unless you connect a wire from your hull to the metal it won’t Do anything. Or ram it and stay touching it.