Fuel Tank Corrosion on Cape Cruiser

F

forrest

New member
I pulled my fuel tanks because I wanted to raise them up to allow the fish blood to wash out to the sump pump better. It really gets to stinking under the tanks during the fishing season. As you can see from the pictures that I posted in my album, Cape Cruiser installed a diagonal raised strip of flooring to support the center of the tank. It goes the wrong direction to aid in water flow to the sump pump. The picture doesn't show all the crap that was trapped under the tank. I cleaned up at least 1/16 inch of dried nasty stuff off the floor before the picture was taken. When I cleaned up the bottom of the tank I found some pretty serious pitting that was occurring between the diagonal raised floor strip and the fuel tank. I've only used the boat four seasons so I'm surprised at how fast it occurred. I noticed that the motor installers didn't hook up the gas tank ground wire (last picture) so that might have been part of the problem. On a positive note I didn't have any water under the cockpit deck. Anyway I thought I'd give you Cape Cruiser owners a heads up. I don't know if C-Dory Ventures are made the same way or not.
Forrest
 
Hi Forest,

Under the forum that deals with fuel systems (p.1), you'll will find our notes about the potential for fuel tank corrosion and the 23' Venture.

I'm glad you found no water under the aft deck. With regard to the grounding wire, the guy who rigged our motor said Honda didn't allow the the engine to serve as the bonding ground. As I see in your picture, the connector is by the engine bolt. I ran a separate bonding wire to a its own bonding/ground plate on the stern.

Tim and Dave Kinghorn
 
Forrest,

Thanks for the heads-up on the corrosion, and particularly the one about the grounding strap. I'll have to check it when we get back to AZ.

Best,
Casey
 
I'm guessing that the boat has a raw water washdown pump and that you use it to keep the deck as clean as possible.

I'm wondering if the "crud" that gets on the deck while fishing (and later causes that fishy smell) is helping to keep salt water trapped against the tank where that support rib is. My thought is that the corrosion is from salt water, and not electrolysis. I would expect electrolysis to be all over the tank, not just at the support rib.

I think I would coat the tank (at least the bottom) with something that will act as a shield between the aluminum and the salt water. Probably clean up the pits and fill with a thickened epoxy product.
 
I've not been a fan of aluminum tanks for this very reason. In this instance a couple of good coats of epoxy like West System or the like will seal the bottom of the tank. One wants to provide a barrier coat with aluminum. It does interesting things when mixed with electricity and sea water

George
 
I'm certainly not the expert, but you may find this article by Pascoe to be of some help: http://www.yachtsurvey.com/corrosion.htm

I believe that the section dealing with crevice corrosion applies in your case.

I'm also quite leery of painting aluminum, having owned a painted aluminum boat. If done correctly, it is awesome, but if not done correctly it can cause corrosion itself.

I wish I had a solution or suggestion.

Best of luck,

-Sarge
 
Aluminum fuel tanks are fine, if properly installed. In this case, I would fill any of the pits with JB weld. Then clean and etch the entire bottom of the tank (and sides)--coat with Stronchium Chromate two part epoxy primer (several coats). I would finish with a good coat of urethane paint.

For the bottom, I would put in several strips of plastic, runing fore and aft--after removing or grinding down what is in place currently. Secure the plastic to the tank with 5200. Thus will allow the water to run under the tank, keep the tank away form the salt water (which I agree is a cause of the problem). This makes me think that perhaps this tank was not of of the salt water resistant series of aluminum.

I think that you can still safely use this tank--but usinging an epoxy coating and barrier coat is essential, as well as elevating the bottom of the tank so that water does not pool under it.

In the past, I had a fuel tank which was far worse than this, and after the first stages of restoration, then covered it with several layers of 6 oz glass--which I warped around the sides of the tank. 10 years later it was still functioning well.
 
I am in Sacramento, and the boat is in Seattle. Therefore, I can't check my concern until I get back up there for the boat show, but I thought I would share my concern and hope that others more knowledgeable than I might comment.

If you bond to the engine bolt through the stern with what looks like #10 wire, is there a chance that if the negative ground from the engine to the battery is disconnected (corrosion on terminal, removing, mechanical break, etc.) and the motor were cranked, that the high starting current would return to the battery through the bonding wire? If so, the very small #10 or even a #8 bonding wire would probably ignite.

Normally, you would connect the bonding circuits to the negative side of the battery. On our boat, the bonding circuit goes to its own grounding plate underwater at the stern and is also connected to the negative terminal of the battery. Calder (Boatowner's Mechanical And Electrical Manual (page 214) states that a bonding cable attached to the engine should be able to handle the starting current of that engine. That is, it should be the same size as the negative lead from the battery to the motor.

Feel free to comment. But if I'm right, a lot of boats are at risk of overloading a bonding wire which could ignite. In the case of our venture, this would be right next to the fuel tanks and low where fumes would likely be found if there were any leak.

Tim and Dave Kinghorn
 
Hi,
When I removed my fuel tanks there was no ridge on the floor. My boat a 23 Venture is an an 08 and had two rubber strips glued to the bottoms of each of the aluminum tanks to keep it off the rear floor. pictures shown in our album. No signs of corrosion yet. I guess next time I remove them they are getting some zinc chromate and epoxy paint. Good info thanks
D.D.
 
Be cautious of "rubber" strips, since many of them have sulfur compounds which will rapidly corrode aluminum. This is why plastics are recommended. There are certainly some silicone matierals which are "rubber like"--and will not be either conductive or corrosive.
 
thataway":1nsth40v said:
Aluminum fuel tanks are fine, if properly installed. In this case, I would fill any of the pits with JB weld. Then clean and etch the entire bottom of the tank (and sides)--coat with Stronchium Chromate two part epoxy primer (several coats). .
Click to expand...

What about the coal-tar epoxies? I thought they were still the preferred coating for aluminum tanks, despite them being a product introduced about 50 years ago...
 
forrest":w374z0j1 said:
I pulled my fuel tanks because I wanted to raise them up to allow the fish blood to wash out to the sump pump better. It really gets to stinking under the tanks during the fishing season. As you can see from the pictures that I posted in my album, Cape Cruiser installed a diagonal raised strip of flooring to support the center of the tank. It goes the wrong direction to aid in water flow to the sump pump. The picture doesn't show all the crap that was trapped under the tank. I cleaned up at least 1/16 inch of dried nasty stuff off the floor before the picture was taken. When I cleaned up the bottom of the tank I found some pretty serious pitting that was occurring between the diagonal raised floor strip and the fuel tank. I've only used the boat four seasons so I'm surprised at how fast it occurred. I noticed that the motor installers didn't hook up the gas tank ground wire (last picture) so that might have been part of the problem. On a positive note I didn't have any water under the cockpit deck. Anyway I thought I'd give you Cape Cruiser owners a heads up. I don't know if C-Dory Ventures are made the same way or not.
Forrest
Click to expand...

Maybe I missed your reply.

Did you repair and paint the tank?

Best
 
Karl,
Yes, the coal tar epoxies are excellent--but not really necessary, unless the tanks are going to be in constant exposure to salt water. The Stronchium chromate primer 2 part epxoy works well.
 
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