Aluminium deck plates, stainless fittings!!!

[ecb]

Hi folks

Seeking some advice. I have lovely boat - Dehler 22 - which is wonderful to sail and very well built APART from the fact that all the deck fittings are bolted into aluminium plates inside the laminate. Ergh!

I have noticed some bulges in the laminate under the stanchion base/sockets. I have had a poke and the aluminium plate is powerdery and like cardboard. I guess some salt water has worked in and over time the aluminium has fizzed away with the stainless (is the white powder I'm finding in the anchor locker aluminium oxide????).

This winter I'll obviously need to do some remedial work.... questions

(1) Is there anything I can apply to the weakened aluminium to clear away the power and cut back to some sound aluminium?

(2) would it be okay to bog the stanchion sockets back in with epoxy?

(3) I can only get access to a few of the bases, some are hidden by the inner moulding, so what's the best solution from 'outside'.

Any advice please?

Cheers

Euan



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[AndrewB]

Oh dear, nasty. I sometimes think boat-builders deliberately mix metals like this not to save money but simply to ensure built-in obsolence. Using zinc chromate paste (eg Duralac) when the parts are originally fitted slows the electrolysis but is not a miracle cure in the long term.

Once aluminium starts to go, it swells and admits water which speeds the reaction. The aluminium oxide powder and goo that is produced is caustic and can damage nearby materials (don't know about GRP but wood certainly).

I've tried all sorts of solvents for cleaning back to bare aluminium where this has happened. Nothing is really effective, other than wire-brushing and painting, preferably with epoxy, which offers a barrier that slows down recurrence.

Remedial action is essential but I think you face a difficult choice. Clearly the stanchion bases and other fittings do need to be adequately reinforced, bodging with epoxy won't survive someone falling heavily against one. The easiest option would mean new reinforcements fitted on the inside of the yacht, not necessarily in the same position as the present ones, by cutting away the inner moulding in selected spots to get access to the underside of the deck. This is going to require ingenuity to make good cosmetically afterwards. Incidentally if the Dehler has a decent toe-rail, another option is replacement stanchion bases that bolt to the toerail rather than the deck.

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[steve_cronin]

A common practice...

...and deplorable but they would probably argue that if it's sealed properly and any damage repaired promptly then there shouldn't be a problem.

I fear that your only SURE remedy is to grub out from underneath and make good.

Steve Cronin

<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[kds]

Re: A common practice...

But then again - a small amount of aluminium seems to produce a vast amount of powdery aluminium oxide, which I would not really regard as caustic.
Ken

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[kds]

Re: A common practice...

But then again - a small amount of aluminium seems to produce a vast amount of powdery aluminium oxide, which I would not really regard as caustic.
Ken

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