Aluminium Hull Corrosion

[Quayside]

I have an AB Alumina 15 ALX which has suffered from the tubes detaching from the hull twice. I'm told that since the RIB has been kept on a saltwater estuary mooring during the season, long term damage will have occurred and a repair is unlikely to last long, and therefore be economic. The operating manual says "It's best to remove the boat from the water when not in use", so I guess no claim against the warranty is likely to succeed. Does anyone have any experience with this kind of problem and repair?

[GuyC]

The title of the e-mail refers to corrosion but the subject is the tubes dataching from the hull. Is the detaching due to a glue failing or is the aluminium oxidising and causing a failure?

If it is the aluminium oxidising, it may be due to moisture being trapped between the tube and the hull which will exacerbate the corrosion.

If you have stainless fastenings through bare aluminium in way of the tube, you may have galvanic corrosion. Anodes help if the disimilar metals are in the water but not really if it is a local thing.

Coating the aluminium and isolating the fixings are solutions if the issue is related to the above.

On the warranty, if the boat is still in warranty and it doesn't specifically require you to remove it from the water when not in use, I would have thought a warranty claim would be worthwhile.

[Quayside]

Many thanks - very useful.

Originally Posted by GuyC

The title of the e-mail refers to corrosion but the subject is the tubes dataching from the hull. Is the detaching due to a glue failing or is the aluminium oxidising and causing a failure?

If it is the aluminium oxidising, it may be due to moisture being trapped between the tube and the hull which will exacerbate the corrosion.

If you have stainless fastenings through bare aluminium in way of the tube, you may have galvanic corrosion. Anodes help if the disimilar metals are in the water but not really if it is a local thing.

Coating the aluminium and isolating the fixings are solutions if the issue is related to the above.

On the warranty, if the boat is still in warranty and it doesn't specifically require you to remove it from the water when not in use, I would have thought a warranty claim would be worthwhile.

[mikehhogg]

The first question I would ask is What Grade of aluminium alloy is the craft manufactured from. is the estuary salt water or brackish and as has been asked is it corrosion or oxidation .

[paulbrown22]

I'm not a metallurgist, but didn't think aluminium oxidation necessarily = corrosion? I thought all exposed aluminium oxidises natural in air, and that effectively forms a protective coating. If exposed to sulphides/salt, then that can react with the oxide layer and eventually corrode the surface, but some grades of aluminium are far more resistant to that than others. I'm not familiar with the AB's at all, so no idea what grade aluminium they use, and if the tubes were correctly glued on, I would have thought that would prevent that area from oxidising much?

How old is the RIB? If it's now happened twice, clearly something isn't quite right with how it's been done to date, unless maybe that's twice in e.g. 20 years, which might be reasonable! Preparing aluminium properly for any type of surface coating or adhesive is a very time consuming process, and needs doing properly if you want it to last.

Certainly our 100% aluminium 41' sailing yacht has lived in salt water for most of it's 21 year life, and the oxidised bare surfaces have barely changed since the first couple of years. Our only tiny bits of corrosion, as you say above, are where dissimilar metals (particularly stainless steel in our case) weren't isolated from the aluminium quite as well as they could have been, which is something that yacht manufacturer has now massively improved in the intervening years.

[Quayside]

Thanks everybody - I'm going to talk to the boat yard next week to get their diagnosis. These replies have helped arm me for that conversation.