Aluminium boat corrosion

[Heckler]

Am in to youtube vlogs and watching WhiteSpotPirates, a young German girl bought an aluminium boat in Panama to "live the dream"
Very enjoyable and she is turning out to be a serious PBOer! Just watched where she lifted the boat out to antifoul, had a pressure wash and found some oxidised patches and small holes therein under the first coat of hull paint under the antifoul. She stripped the wholl lot of and has had them welded up but the question is, what will have caused this?
It was flakes of white oxide under the coatings of two part epoxy primer and antifoul.
Stu

 

[NormanB]

Could have been non aluminium metal particles causing local galvanic corrosion (steel, copper) in a damp bilge.

Her and her oppo recently installed a new beta on their ownsome too. Very resourceful young lass.

 

[lpdsn]

I've been told that the best way to sink an Aluminium boat is to drop a few copper coins in the bilge.

 

[William_H]

Aluminium dinghies and small boats are very popular around here. They seem to corrode after some years where salt water is left in the bilge. Pin holes usually near the keel. Even after a fresh water hose out it seems any water left is sufficiently salty. Dangers are in leaving boat on a trailer bow down. They need to be stored stern down with bung removed. They are lighter than GRP but certainly don't lasy as long. olewill

 

[AntarcticPilot]

I've been told that the best way to sink an Aluminium boat is to drop a few copper coins in the bilge.

Or break a mercury thermometer or barometer. Mercury is so dangerous to aluminium that its carriage on aircraft is banned; it forms an amalgam with aluminium that then oxidizes very rapidly. A tiny amount of mercury can destroy an awful lot of aluminium! See https://www.youtube.com/watch?v=IrdYueB9pY4

PS, the time lapses in the video are over shortish periods - a few hours, and there's no information about the alloy used - I doubt that Home Depot sells pure Aluminium! A drop of mercury lurking out of sight for a while woudlcertainly destroy an awful lot of aluminium.

 

[rogerthebodger]

Even the copper trimmings from electrical wiring in an aluminium hull does cause problems with this kind if corrosion.

 

[vyv_cox]

Aluminium relies on formation of a passive layer just as stainless steel does. This results in the formation of pits at any surface imperfection. Once started pits just keep going by crevice corrosion mechanism.

 

[savageseadog]

Even the copper trimmings from electrical wiring in an aluminium hull does cause problems with this kind if corrosion.

Is there any chemical cleaning system that can clear up bits of copper without attacking the Aluminium itself?

 

[GHA]

Couldn't watch that all the way through, too awful, poor girl!

Such is the cruising life, from ultra high to awful low and no real choice but to sort it out.

 

[Heckler]

Could have been non aluminium metal particles causing local galvanic corrosion (steel, copper) in a damp bilge.

Her and her oppo recently installed a new beta on their ownsome too. Very resourceful young lass.

Indeed. Me and the Admiral have just binge watched the first year. I like the bits where she fixes the camera and walks away ; ) Having said that my better half is as good with the tools as her and just as pretty! Vyv looks as if he has answered the question, either water under the epoxy coating under the antifoul or water in the bilges long term.
Stu

 

[Shearmyste]

Having owned a Ali boat for the last 3 years (she was built in 1986) we have found local areas of corrosion but only under painted surfaces, after finding my first bit of this and doing a bit of home work it appears that ali will corrode under painted surfaces if the painted surface has a small defect, Aluminum protects itself by corroding and the layer will then make the ali passive when painted the ali remains active rather than passive, and the result is poultice corrosion, of which there are two types: dry, identifiable by a white powder, and wet, which produces a white goo. This is probably why the French manufactures tend to not paint the hull above the waterline where small defects can be caused easily.

 

[Lon nan Gruagach]

have to be very careful welding ali too, use the wrong alloy and you may as well just leave a hole there.

 

[Kelpie]

Aluminium dinghies and small boats are very popular around here. They seem to corrode after some years where salt water is left in the bilge. Pin holes usually near the keel. Even after a fresh water hose out it seems any water left is sufficiently salty. Dangers are in leaving boat on a trailer bow down. They need to be stored stern down with bung removed. They are lighter than GRP but certainly don't lasy as long. olewill

OTOH, simple open workboats made of alu can last three decades or more with almost zero maintenance.