Protecting an aluminum fuel tank from corrosion

[Tessellate]

Any ideas on the best way to protect an aluminum fuel tank I have in the bottom of a lazarette? It can't be moved, and this lazarette is our only one - so it provides all of our cockpit storage for a massive amount of cruising gear (including wet salty things like bumpers and docking lines).

The tank is basically the entire floor of the lazarette - I often get into the lazarette and stand or sit on the tank because this is also the only access to the steering cables and one side of the engine.

Last year I bought an "antifatigue sponge mat" from McMaster Carr, and laid it down on top of the tank. I thought this was a splendid clever solution, but now a year later I discovered it's just trapping salt in welts in some areas. I know the tank won't last forever (it already had some minor pitting on the top when we bought the boat), I'm just looking to preserve it as long as possible.

Is there any better option than just leaving it bare and cleaning it regularly? To clean it we have to pull all the stuff out of the lazarette. And I don't like the idea of my shoes grinding dirt and salt into the surface. Really instead of an antifatigue mat I need an anticorrosion mat.

[a64pilot]

Normally I'd say use aircraft fuel tank sealer, but that stuff ain't cheap and since it's not going inside of the tank it may not be required.

I'd contact the local spray in bed liner people, I have seen lots of stuff Rhino Lined, work boat decks etc. and it is of course water proof, flexible and tough.
I'd stick with Rhino Liner though, some of the others are more plastic than rubbery and not nearly as flexible I don't think.

I have not seen good results with the DIY stuff, not like Rhino Liner anyway.

[Cheechako]

The top is probably the least likely failure. The bottom is prone. Anywhere the tank rests on something, water is trapped and it corrodes. If the tank is resting on a flat surface... not good. You could just use Dri Dek product on the top for protection, it allows the surface to breathe.

[Tessellate]

Originally Posted by a64pilot

I have seen lots of stuff Rhino Lined, work boat decks etc. and it is of course water proof, flexible and tough.
I'd stick with Rhino Liner though, some of the others are more plastic than rubbery and not nearly as flexible I don't think.

Interesting idea, and I see Rhino Liner is local to Seattle. Is it sold to consumers though? It doesn't look like I could do it myself, since their website talks about applicators (professionals)?

[Tessellate]

Originally Posted by Cheechako

The top is probably the least likely failure. The bottom is prone. Anywhere the tank rests on something, water is trapped and it corrodes. If the tank is resting on a flat surface... not good. You could just use Dri Dek product on the top for protection, it allows the surface to breathe.

Right, understood. The bottom of the tank fortunately is pretty well done I think. But the top has a few 1/8" deep pits (approximately), and none on the sides (and I can't see the bottom) - so I'm just trying to deal with the problem I know of. Not a high priority problem at all, I just wondered if CF folks knew of any innovative protective coverings.

Dri Dek is like what I was thinking. Dirt and salt water will fall into the holes, but at least I'll see it, and it'll breathe.

[a64pilot]

Originally Posted by Tessellate

Interesting idea, and I see Rhino Liner is local to Seattle. Is it sold to consumers though? It doesn't look like I could do it myself, since their website talks about applicators (professionals)?

No, they come to the boat and do it, they do it all the time in Georgia on shrimp boats and the like, not much tougher and slip resistant surface than Rhino Liner, course if it will hold up in a truck bed to concrete blocks being tossed in, it's pretty tough.
It is not a DIY thing, but it's not that expensive either.
Dri-Deck of course comes in 12" squares and is very tough and easily removable, but it's not going to keep the tank clean and dry, it could be argued it will do just the opposite. I put it in my last boat that we dove out of a lot and I didn't want to bang the floor up with dive cylinders and Rhino Liner would have been ugly, and you had better like it, cause your never getting it off.

[Colin A]

For a coating like a bedliner you can try Durabak they sell it for marine applications it's like a think paint.

[Dsanduril]

the two traditional approaches would be a coal-tar epoxy coating or a zinc-chromate paint. Both could be done in place and both require the right surface prep to be effective. Then maybe Dri-Deck or similar on top to protect the coatings from dings.

[a64pilot]

Zinc Chromate paint has been verboten for years in aircraft manufacturing, but it can be had still, it's that sort of lime green you used to see aircraft primed in before the finish paint.
it is available here in rattle cans, but it is not suitable as a top coat, it's soft and scratches rather easily
PTI SPECIALTY PRIMERS from Aircraft Spruce

But, I'd alodine and why not use a good quality LPU deck paint, maybe even anti skid?

[Dsanduril]

Zinc chromate wasn't banned because it is ineffective, but because of its undesirable health effects on the people who worked with it every day. But the chrome toxicity that caused it to be a problem is a chronic exposure risk, random acute exposures are not as significant. It's actually one place where "amateurs" may still be able to exceed professional results - on rare occasions working with materials that are no longer available to industry because of chronic health risks. Of course, finding those materials at reasonable cost when they are no longer manufactured in industrial quantities can be a challenge.

To me, zinc chromate is one of those items. Still available in limited quantities, at a reasonable cost, and, IMO, providing better adhesion to aluminum than its replacement(s).

If you use it you have to weigh the exposure risks for yourself.

Another option, that I have heard decent things about, is Alumetron. The company claims that, like zinc chromate, it forms a chemical bond with the aluminum. Have never used it, so....

Alodining a tank in place, in the lazarette could be tough, but with enough care I could see a way to get it done (or at least the top of the tank, which is the problem area that catches and holds most of the salt/moisture).

[UNCIVILIZED]

Yes, zinc chromate is still available. I ran across a good deal on some yesterday (in quantity), when looking for some paint. But with aluminum, prep's still key. Which to me means acid etch & alodyne.

Hadn't thought about Rhino Liner, but like the idea. KISS, tough, inexpensive (relatively). How tough is it to pull the tank out of the laz. so that they could do it completely?

Different tactic, & one which might make sense even after coating the tanks. But what about building a "shelf" overtop of it. Or rather, call it a 2nd floor for your laz. built overtop of the tank. To both assist with keeping the wet directly off of it, even when it's coated. Plus to reduce the flexing from your climbing on it. And it'd probably help with shielding it a bit from water flowing down it's sides & getting underneath of it too.

[Squanderbucks]

While your may coat the top and make it look better and feel that you are extending the life of the tank - keep in mind that as was pointed out earlier that the bottom (especially seams and corners) are where the corrosion is usually the worst.

A friend of mine had an aluminum tank corrode through while on a trip to the Bahamas and didn't notice it until he had 75 gallons in the bilge while en route between islands. Unfortunately it was right after a fill up and he had little room to transfer remainder into other tanks as they were all full.

If this is your only tank it could be a very unfortunate trip when it begins to leak - and if it decided to leak at the dock - your bilge pump would start emptying fuel into the water and you would be turned in by the dockmaster for an EPA violation and those fines don't even start with a low number based on what I see posted at the local fuel docks. They worry about a few cup fulls.

If the tank is over 20 years and shows 1/8 inch pitting where you can see it I would recommend taking it out and replacing it. Probably have to be cut out in pieces and replaced with either several smaller ones, cutting out and replacing the hatch, or having a custom one built of fiberglass in place (if diesel).

Can't see any positives in leaving in place unless you plan to sell boat soon and can pass the problem on to the next owner.

Any aluminum tank should have several small footprint supports elevating off the surface and not be walked on directly. So the shelf above it mentioned earlier post would be a certainty after the replacement(s) is made should you go that way. I would make the new "floor" removable to allow for inspection and cleaning of the tank from time to time.

[Cheechako]

Yep, had a 3 month trip spoiled due to slow leakage of a tank a few years ago. Pretty much spent most of the trip determining which of the two tanks it was, keeping the bilge clean without bilge pumping, transferring fuel, airing out the diesel smelling boat.. etc. Turned out the bottom was leaking on one, and about to be on the other. New bottoms were put on the tanks eventually.

[Dougtiff]

You could fiberglass the top and down the sides and there is a company that makes a inspection port in various sizes that can be installed after cutting the round hole, that gives you access to the inside.

[UNCIVILIZED]

Originally Posted by Squanderbucks

While your may coat the top and make it look better and feel that you are extending the life of the tank - keep in mind that as was pointed out earlier that the bottom (especially seams and corners) are where the corrosion is usually the worst.
Yeah, that's why I asked about removing the tank for the Rhino Liner application. I couldn't imagine only doing the top & sides. Wouldn't make any sense.

A friend of mine had an aluminum tank corrode through while on a trip to the Bahamas and didn't notice it until he had 75 gallons in the bilge while en route between islands. Unfortunately it was right after a fill up and he had little room to transfer remainder into other tanks as they were all full.

If this is your only tank it could be a very unfortunate trip when it begins to leak - and if it decided to leak at the dock - your bilge pump would start emptying fuel into the water and you would be turned in by the dockmaster for an EPA violation and those fines don't even start with a low number based on what I see posted at the local fuel docks. They worry about a few cup fulls.

If the tank is over 20 years and shows 1/8 inch pitting where you can see it I would recommend taking it out and replacing it. Probably have to be cut out in pieces and replaced with either several smaller ones, cutting out and replacing the hatch, or having a custom one built of fiberglass in place (if diesel).

Can't see any positives in leaving in place unless you plan to sell boat soon and can pass the problem on to the next owner.

Any aluminum tank should have several small footprint supports elevating off the surface and not be walked on directly.
I think what you're referring to here, are sometimes called "feet". You can even find versions of such at home, on various appliances.


So the shelf above it mentioned earlier post would be a certainty after the replacement(s) is made should you go that way. I would make the new "floor" removable to allow for inspection and cleaning of the tank from time to time.

When I mentioned the shelf idea, making it permanent never crossed my mind at all. As again, it wouldn't make much sense to me.

In my mind, inspecting most of one's tanks is just a standard, periodic maintenance thing. Inside and Out, on all sides.
Nothing lasts forever, especially on a boat.