Corrosion on Aluminium Boat

[castlemaine]

I was looking at purchasing a 2nd hand boat (Quinnie 2000) but noticed around some of the fittings (rod holders, etc.) fitted with Stainless Screws, there was surface corrosion around the fittings. I was put off by this but wondered if this was superficial and could be remedied. No other corrosion was noticed on the hull. Should I stay away from this boat? I believe it was stored on a pontoon most of it's life. Any advise would be greatly appreciated.
Cheers, Castlemaine

[Wear_the_fox_hat]

Castlemaine,
The only way to check is to take the fittings off & see how much the electrolosis (spelling) has eaten into the aluminium. I would say you will probably snap the odd bolt off doing this also. Can be cleaned up with a wire brush wheel in a drill & spray painted with an aluminium etch primer & then painted whatever colour over this. Galmet brand primer & paint seems to work quite well. Duralac must be used on all fittings at any point of contact, nuts & bolts included. Why manufacturers don't use this on boats from new has got me stuffed. This prevents electrolosis & stops nuts & bolts from seizing up. Even use this between aluminium fittings as there are different grades of aluminium. I speak from previous experience. Just be wary of this boat being stored on & near salt water all the time. I'd be ripping the floor up & checking for electrolosis inside the hull & also getting the water jackets of the motor checked by a mechanic for pitting.

Best of luck,
WTFH

[dnej]

Corrosion can be a big problem under floor. Epoxy paint is normally used, to stop the problem but if this is damaged, pitting can be found. Lanolin is great to use, self heals, and protects the aluminium, from the corrosion.
In the 80's CSIRO, experimented with aluminium,building a box, that represented the under floor of a boat.
They found that if raw aluminium,was exposed to the conditions set up, and salt water added,the water evaporated and formed globules that hung off the underside of the floor.
This contained concentrated salt ,and when it dropped onto bare aluminium, corrosion occured.
Quicksilver boats (in Mossman, I think), use lanolin,and the only problem they have had, is where they couldnt get coverage, on the aluminium.
Definitely be careful with this issue
Hope this helps
David

[Jeremy]

David,

I thought that the aluminium oxide which forms on bare or new aluminium was sufficient to prevent corrosion by salt water, but not electrolysis. How else would unpainted tinnies stay afloat?

I am interested in more info on this.

Thanks....Jeremy

[seatime]

castlemaine

may only be superficial because of the electrolosis with the SS. lose the SS bolts if u can, clean and oversize the holes if needed.
try and replace with alloy rivets or bolts. if there're not load bearing, alloy will be ok. paint or self-amalgam tape works as a barrier too.
look hard 4 any paint disturbances, it could be hiding corrosion.
regards

[dnej]

Jeremy,
I am not really up with the technical side, but the reason I got involved, was because of the craters in my old girl only under the floor. Of course, the aluminium back in the 80's was different as well.
My boat was made for the Navy, and they first thought it was battery acid, causing the problem.
Thats why I made the call, to find out what the cause was.
The results I mentioned,came from the then CSIRO. Wonder if they are still available.

The Quicksilver Boats, only had problems, where the Lanolin didnt reach, apparently round a box of some sort.
I have stopped the problem with the lanolin grease for the last 3 years.
Regards David

[hussy]

i have found that if i clean up what i can repaint the place an anode on some unpainted will solve your problem, it works like a charm . hussy