The Offshore Voyaging Reference Site

Q&A Inspecting an Aluminum Boat Hull

Question

Member Michael Asks:

…I am looking for a used aluminum yacht…I have read all your articles on how to care for an aluminum yacht. However, how to look for serious problems on a used (25 years old) aluminum yacht?

I know that I can check the electrical installation with a meter, but can I find any alarming signs of electrolysis in a yacht that is in the water? Are there any other areas on a used aluminum yacht that I should pay attention to?

 My question concerns hull corrosion and the resulting lower strength of the hull.

Answer


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Michał Palczyński

Thank you John for so detailed answer. I just ordered silver chloride reference cell.

George L

And make sure the engine screws are A4 stainless and that an insulating agent like Ted gel is used so you won’t get corrosion between the screws and the access panel

Michał Palczyński

Thanks. But that’s for later if I buy this boat. Corroded screws are not a deal breaker for me 😉

Kors Slot

I would also recommend you also to check visually inside the water tanks.
Quite often they are corroded, specially with older boats

Ron Riley

I have a naive question: what does aluminium corrosion in the bilge look like? I have Googled but still don’t know. How does one distinguish it from harmlessl scurf one might find in a bilge?

Neil McCubbin

Agreed with John and all the comments.
One detail, use Tef-Gel (made by USS) on all SS screws on the boat. “Ted-gel” os mentioned. Perhaps a typo, but beware of the several knock-offs with names very similar to TefGel.
Emphasize looking inside the water tanks. If they are unpainted, and have never had chlorinated city water in them, probably OK. They may have hundreds of white pustules a few mm diameter.
If there is not a decent visual access to the tanks, I would insist on one being cut for survey, if that is at all possible.
Look carefully at any beautiful recent paint. Some years ago I was in Garcia’s yard and saw them cutting off and replacing most of the bottom plates. The boat had sailed from Australia to Europe with a wind generator using the hull as the negative “wire”, been seriously pitted, then filled and painted for selling. Not surprisingly, Garcia’s customer and the previous owner were in court.
Above based on 20 years sailing an aluminium boat, with (so far) no corrosion issues, following John’s advice, and meeting a goodly number of other owners. Don’t let the age alone of the boat put you off.

Michał Palczyński

Kors and Neil,
thank you for your suggestion about checking inside the water tanks.
It looks from the pictures that the access is good so I should be able to look inside through the inspection hole.

Dan Manchester

As well as the shaft tunnel, I’d suggest also looking closely anywhere steel, stainless, or any other metal, is in contact or even within cooee of the aluminium. I’ve inspected many offshore structures where the Al has completely disappeared from galvanic (dissimilar metal) corrosion. Check behind base plates even if they have rubber insulators, remove some bolts and check bolt holes for enlargement. In my experience you don’t need contact for dissimilar metal corrosion – if the components are close enough, and wet and salty enough, the electrons find a way.

Michał Palczyński

Hi Guys,
I’m doing inspection on that 24 years old Aluminium yacht now.
Today I’ve found some underwater corrosion under the paint.
At this picture you can see the worst area:
https://drive.google.com/file/d/1nBz1ZDXBK1w3LkEcYvZfHVkCI4ojTven/view?usp=sharing
I’m aware that on such a old boat there will be some corrosion. However, I’m wondering could this level of corrosion is something to go away?
Electrical check tomorrow.

Thank you for any advice.
Michal

Michał Palczyński

Hi John,
thank you for reply. We just went back from inspection. Electrical check with silver chloride reference cell showed problem with stray current (decrease of potential from -1,026V to -0,886V when connecting shore power). Then we took the boat from the water and have found corrosion (pitting) around the hull. Also deep galvanic corrosion around two thru hulls.
But I’m still not 100% sure if this is enough to give up this boat (I can probably get very good price and I like other aspects). The aluminium in the bilges looks like new (except around those 2 thru hulls).

I think I need a consultation with good marine surveyor that knows aluminium problems. Can you recommend anyone?