Proper Installation of Aluminum Fuel Tanks

[CDK]

Originally Posted by Stumble

1) Aluminium is self oxidizing in the presence of oxygen, this creates a very hard, almost impermiable layer of Al-oxide that does wonders to prevent corrosion.

2) In order to bond epoxy to Al you have to sand away this layer to bond to fresh metal. So now you have removes the Al's naturam protective coating to substitute your own.

3) If there are any cracks, defects, pinholes or other wats for water to access the bare metal it will most likely be through microscopic holes... making it almost impossible for the water to wash away or dry. This means that crevis corrosin is going to occur, and it will be almost unstopable once it begins.

That is not quite true.
You cannot sand away the aluminum oxide layer because the bare metal immediately reacts with oxygen again and forms a new layer. What you do by sanding is creating a surface that under a microscope looks like the Sahara after the Paris-Dakar race. It may provide a better mechanical holding ground for the paint but the bonding surface is still an oxide layer.
Only on areas where other elements like chorine or sulfur were present during the sanding process, no true aluminum-oxide will form, opening the door to corrosion.

[Oceannavagator]

Pardon me for just jumping in but I own a 20 foot shamrock with two under deck tanks. The builder foamed the original tanks in and most of them last 15 years or more. The general consensus on the shami forum is to coat the replacement with POR 15, a extremely tough polyurethane coating, and then foam them back in place. The POR 15 product is much better than epoxy because of it's flexibility. Also, using the densest foam will help keep moisture out and the tank in place.
Mike

"The general consensus on the shami forum is to coat the replacement with POR 15" - Many people are replacing these tanks after, more or less, fifteen years, are they?

Do not cover the Al with Epoxy! The resin will get hair cracks after a while due to the different behaviour when temperature changes. Al is a extremely good heat conductor, Ep is not! And fully cured Ep is hard and does´nt bend, the thin tank plate does.
A chlorine based paint, or some PU paints (should both be classified for exactly the use on Al), does a better job. Never foam a tank in! There is no foam on the market that withstands water ingress or getting brittle over the time in marine environment. No matter what the industry tell us, they cannot hold their promise.
a bit aside:
The foam in a enclosed structure (deck for example) is theoretically a safe bet, in everyday use it is not! Believing that haircracks do´nt happen, is like the bikers belief never to fall off his bike. It may happen though..........

Richard

[Mike Sibley]

Boy, so many different methods and so many different opinions! The more I learn, the more confudsed I get.

I originally thought that the article by David Pascoe was the solution, until I tried to implement it on a scrap piece of aluminum. I'm sure a professional could do a great job, but when examined closely, my work always seemed to generate a small crevice at some point. This led me to search for alternatives.

At present, I am leaning toward just resting the tanks on two inch strips of 1/4 inch neoprene. The original mill steel tank was installed this way and it lasted thirty years without a leak. I guess I will not epoxy the bottom of the tank.

Thanks to all for help.

Originally Posted by Mike Sibley

At present, I am leaning toward just resting the tanks on two inch strips of 1/4 inch neoprene. The original mill steel tank was installed this way and it lasted thirty years without a leak. I guess I will not epoxy the bottom of the tank.

Thanks to all for help.

No complaints from a boatbuilders view. But using "Armaflex AF" instead would be even better.

[Oceannavagator]

Originally Posted by mark775

"The general consensus on the shami forum is to coat the replacement with POR 15" - Many people are replacing these tanks after, more or less, fifteen years, are they?

They are replacing the original Foamed In tanks after 15 years. No one knows how long the coated tanks last yet as there has been no failures. As far as the foam goes; 15-20 years isn't enough for you? I replaced my tanks last year, my boat is an 1986 model, the one tank that had corroded through was corroded on top of the tank where the foam wasn't present. I had to use a engine hoist to break the bond of the foam on the tank bottom to get the tank out of the boat! And then chip the old foam off of the fiberglass compartment! Use the two part marine foam, 8 lbs per cubic foot, it sets up like wood, you could drill and tap the stuff. Don't buy the home sealant foam in a can, which is what I suspect has given the problems in the past.
Mike

Originally Posted by Oceannavagator

Use the two part marine foam, 8 lbs per cubic foot, it sets up like wood, you could drill and tap the stuff. Don't buy the home sealant foam in a can, which is what I suspect has given the problems in the past.Mike

All foams Mike are troublemakers, believe me ALL. But of course some do not fall off their bike.

[Oceannavagator]

OK then, Let's fasten it down with stainless, oh yeah dissimilar metal, oops, maybe make the tanks out of stainless, whoa, coast guard says no ferrous metal tanks under deck, Ok lets do a Fiberglas tank, wrong answer, alcohol fuel problems, maybe we'll pour 20 or 30 gallons of concrete around the thing, oh oh, that weighs more than the fuel and it eats up aluminum. I guess the only thing left for you is asking Captain Kirk for a spare magnetic containment field while he's low on dilithium crystals.

Ok, foam don't last forever but it will last 15 or 20 years and who knows, you may fall off the boat before then.
Mike

[Guest62110524]

Originally Posted by CDK

That is not quite true.
You cannot sand away the aluminum oxide layer because the bare metal immediately reacts with oxygen again and forms a new layer. What you do by sanding is creating a surface that under a microscope looks like the Sahara after the Paris-Dakar race. It may provide a better mechanical holding ground for the paint but the bonding surface is still an oxide layer.
Only on areas where other elements like chorine or sulfur were present during the sanding process, no true aluminum-oxide will form, opening the door to corrosion.

i dunno whether any of you have heard of ALODYNE? we use it, used in aircraft industry and been around a 100 years, drill is, sand, wash with acid cleaner, hose of and then when STILL DAMP, spray from a PLASTIC sprayer , leave til it goes bronzie and there, no more oxidation

My tanks don't leak a drop after 30 years. If 15 years is the benchmark, I guess I should have just been happy buying my third set this following winter. In 1979, tanks were roughly $1 / gallon in these parts. Now they are $10.
I, and others are trying to help, here. There is actually not much disagreement - If foam is used, it is wrong - period. Pick-ups should be absolutely in the lowest part of the tank (one wants **** out of the tank and into the filters - not slithering around waiting for a rough bar-crossing to clog. No copper alloys near the tank. No Racors/Dahls/whatevers - they (especially Dahl) leave too much room for dirt/leaks/mistakes. Spin-ons only.
After all that, the tanks are going to be set on pieces of wet neoprene? Jeeze, why do I bother? For some that don't already have their minds made up, I 'spose.

One version of a proper fuel filter/oil pump-out shelf (mine) on small, simple workboats (on boats that work, ease of maintenance/service take precedence over looks). When redoing tanks, redo filtration, as well. Note that two absorbs fit perfectly. Outboard bulb is for priming filters. Oil pump-out should be wired but note height of outflow is just shy of height of jug of Delo. Drag-pointer vacuum gauge is de rigueur. Don't give me crap about tools laying about. Vicious **** has not landed one tool off of that shelf. Don't notice the fuel in Systems Three container - it is lubberly.

That tank for my Espar is something like ten years old. Powder coated and still looks like new.
Notice the feet welded on for mounting on web-frame. Tank does not rest against that web-frame but stands off about 1/4".
I know of a 60's Marco with tanks built like Woosh said - that don't leak.

[Guest62110524]

all v tidy MArk
i LIKE TO USE SS, with flares, tight R tube benders . particularly in long runs, ss stays true and straight, whereas coiled copper, never looks 100% looks like you are using gunmetal or bronze T,s
Also use ss for 5/8 and 1/2 hyd winch lines, flares again as they cost nothing compared with Swaged fittings

You are right, again. I was poor and saved money, then lazy.

[tightfits]

2x2 angle with 1/8"-1/4" 40drm rubber cemented to angle. Hard tabs for mounting. Use all ss hardware with plenty of anti-siese. Eliminate the plywood if possible, use alum.