Do you know what kind of protection is used for aluminum ship plates?

Hey guys!

Recently, I saw this kind of ship, and something caught my attention: this ship doesn't use antifouling or any other kind of paint on its aluminum plates.

So, how do U think that they protect these ships?

have you ever seen this kind of treatment ?

 

Welcome to the forums Angel.
There are some aluminums that do not need cathotic protections if you are smart about other materials and electrical grounding. Mostly 5083 and 6061. A lot of that protection is depenedent on water, use cycle, and speed. Additionaly, there are modern coatings which can be applied at build, which if maintained, can significantly reduce the exposed substrate.

Plan B Marine operates in NYC...so colder fresh or brakish North Atlantic waters. So there there are lots implications about operations here.

 

Welcome to the forum Angel,

Echoing JEH, but with the caveat:

Hull plating is 5000 series, so there is no need to paint the hull, so long as due diligence is done on any items being exposed and/or penetrating the hull, to prevent a galvanic cell.
6000 series is not used below the waterline....i know some (amatures) do, but 6061 for example has high copper content and it thus prone to corrosion when in a environment that would promote such, unlike the 5000 series.
Class do not allow 6000 series below the water line, for this reason...and historically, it is why 6082 was created, as it has 3 times less copper content than 6061 and equal/better strength.

 

Keep in mind, an oxide forms on these, so the actual exposure is not Al, but some oxide. I do not know enough about the chemistry to offer a better answer, but aluminum oxide is more stable and sort of automatic. Of course, the process can be enhanced to anodizing, etc.

I’m secretly or not now hoping for more details on the oxides from someone more knowledgable.

 

The oxide of aluminium is a film of Al2O3 or Al2O3.H2O of various thicknesses, though it is nominally around 50 angstrom thick.
This protective film provides aluminium with its characteristic resistance to corrosion which many often refer to; which is why most small boats in Australia are left unpainted. This film forms rapidly (in milliseconds) that inhibits the bulk reaction. In addition, if the surface of aluminium is scratched sufficiently to remove the oxide film, a new film quickly reforms, in most environments.
Such that, as a general rule, the protective film is stable in aqueous solutions of the pH range 4.5-8.5, whereas it is soluble in strong acid or alkalis, leading to rapid attack of the aluminium, not a favourable environment.

 

Thanks Ad Hoc for the clarification! It's been a while since I worked with Al, and most of that was deck houses and UUV frames (i.e. short exposure).

 

The responders have clarified the issue of whether painting the aluminum for corrosion protection is necessary.
The OP had mentioned anti-fouling in his first comment.
Barnacles and weed growth can occur on an unpainted aluminum surface.
If this is an issue in the waters where you intend to boat, I would recomend Micron CSC, from Interlux, which is an ablative coating and properly applied works great with aluminum hulls.
There are other equally effective anti-fouling paints in the marketplace.

 

Class do not allow 6000 series below the waterline . How much 6082 is ocean water resistant ?

 

Working with aluminium | Interlux https://www.interlux.com/us/en/boat-painting-help/expert-advice/type-of-antifouling-used-on-aluminum
some choices from Akzo.

 

It is very good....just not as good as the 5000 series.
The issue is more exacerbated if you do not pay due diligence to having 'dissimilar' metals in contact with the ally, when submerged in seawater.

Since there is an electrical cell between the 5082 and 6082 as well, via the electrolyte of seawater, which is some conditions can exceed the threshold for corrosion to occur. Which is why mixing the two, in contact with seawater is no longer advised.

So, if you have 6082, the question would be where is it being used and what if anything is it attached to or with.

 

That looks like an advertising photo. A new boat that is kept on a trailer should not need antifouling. Also, to keep it shiny, some meticulous owners wax their boats.

 

good morning Ad Hoc
which rule shows this no allowance please?

 

Do you mean, not allowing 6000 series below the waterline?

 

yes I do

 

Here from LR: