Aluminum fuel talks
I have a 1973 GB 32 woodie, and as many times the case with old woodies one
of the fuel tanks had rusted through due to water leak around the filler
tube. Three years ago both tanks were replaced with 1/8' 5052-H32 aluminum
tanks. I thought I was set for the life of the boat, but no such luck. One
of my new tanks developed a leak due to corrosion where the tank rested
against a wood member and sea water had leaked on the contact point.
I don't think this can be simple corrosion, but must be due to electrolysis.
I'm not sure what the circuit for electrolysis could be, but my question is.
All through-hull fittings on the boat are bonded together, and might it help
if the aluminum tanks were also connected to this bonding circuit?
Any other advice would be much appreciated. The leaking tank has been
repaired (welded patch) and I now have two non-leaking fuel tanks, but what
is the best way to prevent this happening again?
Bill English
Woodstar, GB 32 woodie
Sausalito, CA
Bill,
FWIW, my Al tanks are bonded. In this forum in the past, it has been
emphasized that you must prepare "bunks" for Al tanks regardless of the
material they rest upon. They cannot rest in water. On a well-built sailboat
I once owned, my Al tank's bottom became porous owing to sitting in bilge
water. Had to weld on a new bottom. Then the bottom and sides of the tank
were painted with coal tar epoxy to prevent a recurrence.
I think that David Pascoe's website explains how to properly install Al
tanks. You can use rubber or neoprene material to separate the tank from
wood or fiberglass. But you still must keep the location dry, and/or paint
the tank with a system which will prevent corrosion. I would do both. I'm
surprised that the manufacturer did not give any directions. There is a big
Florida tank manufacturer whose website includes this advice. The
alternative is to purchase plastic tanks from Ronco or similar and avoid the
whole problem, except for properly supporting and securing them.
Ron Rogers
Any other advice would be much appreciated. The
leaking tank has been repaired (welded patch) and I now have
two non-leaking fuel tanks, but what is the best way to
prevent this happening again?
Bill, what you discribe is common to aluminum tanks, the problem is improper
installation, and is not a bonding problem.
When you install the tank, there should be some material that will not let the
moisture from the wood get through to touch the tank, placed between the wood
and the tank.
This is usually accomplished by using rubber strips, wide enough to cover any
wood that the tank will touch and adhering it to the tank in such a way that
moisture cannot get between the rubber strips and the tank- many folks will
use 5200 as a bonding agent between the tank and the rubber.
It is important to put this barrier at any location where wood can touch the
tank, not just on the bottom.
Good luck, by the way, 5200 has the ability to leap, so you can never get far
enough away to keep it off you.
Rudy
Briney Bug, Panama City, Fl
I once had a fuel tank leak and I did the repair. then I reinstalled the
tank and added a spacer to lift the tank for a day. Then I took some spray
foam and filled the gap between the tank and the support. I seal the space,
waited for it to dry up, then removed the blocks that were holding
temporarily and filled this space with spray foam. Think of the logic behind
this... This airtights the touch to the tank and waterproofs the space where
it touches the tank, If no air touches the vulnerable spot and no moisture
reaches either then you have no corrosion... It also prevents vibration
wear. I really hate rust or rubbing wear or corrosion... and yes the tank
had to be grounded with your common ground on the vessel
Roger
A problem solver...
----- Original Message -----
From: "Bill English" wenglish@pacbell.net
To: trawlers-and-trawlering@lists.samurai.com
Sent: Friday, September 11, 2009 7:17 PM
Subject: T&T: Aluminum fuel talks
I have a 1973 GB 32 woodie, and as many times the case with old woodies one
of the fuel tanks had rusted through due to water leak around the filler
tube. Three years ago both tanks were replaced with 1/8' 5052-H32 aluminum
tanks. I thought I was set for the life of the boat, but no such luck.
One of my new tanks developed a leak due to corrosion where the tank rested
against a wood member and sea water had leaked on the contact point.
I don't think this can be simple corrosion, but must be due to
electrolysis. I'm not sure what the circuit for electrolysis could be, but
my question is. All through-hull fittings on the boat are bonded together,
and might it help if the aluminum tanks were also connected to this
bonding circuit?
Any other advice would be much appreciated. The leaking tank has been
repaired (welded patch) and I now have two non-leaking fuel tanks, but
what is the best way to prevent this happening again?
Bill English
Woodstar, GB 32 woodie
Sausalito, CA
Then I took some spray foam and
filled the gap between the tank and the support. I seal the
space, waited for it to dry up, then removed the blocks that
were holding temporarily and filled this space with spray
foam.
Foaming tanks in place has been a common approach in boats for years, and unfortunately, it is being discovered, now that they have been in long enough, that the foam does not keep moisture off of the tank as well as it needs to.
I'm sorry to have to disagree, but time has proven that this approach is not as good in reality as it seems to be in theory.
In the past couple years, I know of at least 10 boats, who had to have their aluminum tanks removed because of moisture caused holes. In addition, the foam is, in the long run, bad for the wood also.
Rudy
Briney Bug, Panama City, Fl