Protecting aluminum fuel tanks

[rogerbum]

Given the other recent thread about another aluminum tank leaking, I'm wondering if we should hook our aluminum tanks to some kind of zinc to help protect them. On the Tomcat, the tanks won't come out without cutting big holes into the deck but I can get to the ends of them to attach a zinc if that would help. Thoughts? Bob?

[AstoriaDave]

Should not need a zinc if the tank is isolated, I believe. Gotta keep them reasonably dry. I assume they were installed with inert spacers to prevent chafe and to allow air to circulate underneath. I have seen aluminum tanks taken out of fishboats, in service 10 years and they showed no corrosion.

[rogerbum]

In principle, I agree. However, it would appear that in several cases, the tanks are corroding. Maybe they were not properly isolated by the factory, maybe the insert spacers are insufficient. The problem is that I cannot know without cutting the deck to find out. Hence, I'm wondering if there is some useful measure I can take that might prevent problems.

[Sea Wolf]

Roger-

Besides asking our gallery of knowledgeable members with their expert experience and professional understanding,
I'd think this topic would be worthy of asking the technical advisors at a few major marine aluminum fuel tank manufacturers
to see if their is a consensus among the pros that deal with this issue frequently.

At least for me, that would be one avenue to explore in addition to this thread.

Sometimes the pragmatic solution in a problem such as this simply goes beyond what academic theory or common everyday experience would suggest.

Good Luck!

Joe.

[thataway]

The zinc would do no good.
There are several problems--and the major one (not just for C Dory) is that often fuel tanks are not made of the proper alloy. There are a number of alloys which are used for boats--and often different ones for fuel tanks. Tanks often are folded on a brake, and you need a softer alloy which allows the 90 degree folds. (That does not mean that you cannot find a more expensive alloy which will be corrosion resistant.) Remember than many boats are finished raw aluminum, and run for many years in salt water. They do need cathodic protection.

The proper way to install tanks is on top of some inert material--which does not contain carbon--as is in many rubbers. Plastic, fiberglass, and silicone strips all come to mind. They tanks can be adhered with 5200 to the strips.

Many builders coat the tanks with coal tar epoxy. There are other ways. When I re-did the Fuel tanks on the Cal 46, we cleaned, etched, Alodine treated, then two part strontium Chromate two coats, and two top coats of a good marine enamel These tanks were in perfect condition 20 years later. They had been set on top of new plywood floors, which were coated with one layer of fiberglass/epoxy, all ends and bottom epoxy sealed. Set on fiberglass battens, in 5200.

[BrentB]

I took a solar fan and installed to a cockpit deck plate to keep the bilge dry and it works well, and removed before launching . Maybe long fiber optic bore scope with light to inspect most of accessible areas under the tank would be useful

[rjmcnabb]

I agree with Bob: Zn anode would do no good. I don't know if even a magnesium (Mg) sacrificial anode would be good enough.
Rod

[rogerar]

A lot of people for a long time have used Gluv-it for coating aluminum tanks. " On aluminum hulls, Gluvit seals seams and rivets and acts as a barrier coat to minimize galvanic corrosion"

http://www.marinetex.com/gluvit.html