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Coin Underneath the Wooden Floor in Painted Aluminium Boat


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A 5 cent coin has escaped my pocket and gone underneath the wooden flooring in a painted aluminium boat. I've removed the front wooden floor, but the coin has moved somewhere else. To take the main wooden flooring off will be a big piece of work.

Will the coin cause an issue or corrosion if I just leave it there? Unsure where it has gone.

thanks all.


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I know times are tough but if you've got a boat I'm sure your doing ok! :)

Seriously, IMO it shouldn't cause much hassle unless it blocks a drainage point. Although it won't rust out like hooks etc, I don't think it will do any damage to your hull. Let's hope it's not a costly 5cents!

Cheers scratchie!!!

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I'll run the risk of 'troublemaking' and point out that it's galvanic corrosion you have to worry about in this instance. Ie when two different metals come into contact the less noble or more reactive one will corrode. Unfortunately it's aluminium that will be the metal to corrode in most cases. You don't need any external current for galvanic corrosion to occur, but the metals need to be exposed to the same conductive solution such as seawater.

Edited by billfisher
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Sorry TunaSickle, I'm with billfisher on this one. Its galvanic corrosion you need to worry about - put two dissimilar metals in an electolyte solution and the less noble metal WILL corrode.

The fact that your boat is painted buys you time until the paint fails (starting usually at joints/welds where expansion and contraction movement is most concentrated).

Why not try a simple test - drop a 5c coin onto a piece of aluminum in a jar of salt water. Maybe you can post photos of your experiment at say 1day, 1week, 1month !!!!

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I'm thinking that a coin in a jar won't be quite as good.

You'll probably need some air too

I'll run the risk of 'troublemaking' by making two posts on the one thread and point out air (oxygen) doesn't come into it. In chemistry terms oxidisation is the loss of electrons. With galvanic corrosion or in a galvanic cell one metal robs the other metal of electrons. it's also called a Redox reaction (short for reduction/ oxidisation).

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i'm happy to be corrected.


I'll find some water and a jar and some salt and a coin and some Aluminium this weekend

assuming I remember after the Christmas party and start the trial.

Any particular coin or Al?

Is it Iron that needs air or am i mistaken on that too?

Edited by antonywardle
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billfisher has got me worried about making two posts on the same topic....is that an unspoken rule guys and gals???

....Anyway - here is what I remember from my past:

Corrosion - oxidation - is the process of metal atoms binding with oxygen atoms creating an oxide layer - if the metal is iron - the product is FeO2 iron oxide or "rust". If its aluminium the product is aluminium oxide etc.

Galvanic corrosion is a different process - one that does not involve Oxygen per se. As billfisher pointed out "With galvanic corrosion or in a galvanic cell one metal robs the other metal of electrons. it's also called a Redox reaction (short for reduction/ oxidisation)."

So they are two different processes.

The interesting thing though -- with some metals the oxide layer is actually a VERY good barrier to further oxidation because the oxide layer is impervious to additional Oxygen atoms reaching the metal underneath. The oxide is like a self protecting skin. Aluminium is one of those metals. Aluminium is actually very reactive. Aluminium oxide is very inert. Ever noticed how when you cut aluminium it is really shiny - that's the base metal - and within a very short period of time that shiny metal becomes a dull oxidised metal colour - thats the aluminium oxide that has formed on the surface and no further oxidation takes place. So aluminium gets its durability from its oxide coating.

Iron/steel on the other hand is different. Iron Oxide allows oxygen through and hence the "rust" just keeps going.

An then comes the topic of stainless steel (alloys). From memory stainless steel is an alloy of several atoms the main being Iron/Carbon/Chromium etc... the Chromium binds with oxygen and forms Chromium tri-oxide - impervious to oxygen - that's the shiny skin on stainless steel. If you paint stainless, or mould a plastic handle onto a stainless blade, or leave greasy finger prints on stainless --- at the edge where the stainless steel meets the paint/oil/plastic - you will eventually see "rust". Why??... the Chromium cannot get a 3rd Oxygen atom to bind there and hence some iron atoms are left exposed to bind with Oxygen and then you get good old "rust" on your stainless. So keep your stainless clean guys and just expect that you will get some rust wherever your stainless work joins something else - simple rub with s/steel wool rexposes the chromium and all will be good for a while again !!

Hope that helps Antony.

.... and now that I have completely gone off topic it really is time for that morning cuppa....

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If you use kitchen salt and tap water it would be a "lab" experiment....for it to emulate the real world, we'd have to try to recreate the pH, salinity and mineral content of sea water (or grab a jar of old briny the next time you are out) and we'd also need a piece of aluminium that's two pack coated with some scratches and nicks in the paint.

Personally I'm a naturally curious guy -- so I'd like to see it just to get a sense of the rate of galvanic corrosion - 1day, 1 week, 1 month. It would put a lot of minds at ease I think and what a great way to settle that bar room discussion.

How much time do you have Antony??

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