Installing aluminum fuel tanks this weekend ... rubber to isolate tank from hull?

[piperca]

I have two new fuel tanks that I am installing this weekend. The tanks are shaped to the V in the hull and each has four tabs to attach them to the top of the stringers. With the tanks supported on top of the stringers, there is approximately 3/4"-1" of a gap between the tank and the hull. I was intending on using neoprene rubber pads to add some support to the underside of the tanks; however, I am led to believe the carbon in the rubber will react with the tank. Does anyone have an idea as to how I might isolate the rubber from the aluminum?

I thought about using 1/4" rubber strips and gluing some 1/2" schedule 40 sprinkler pipe to the rubber. I'd run the pipe through my tablesaw to allow a flat spot for the glue ... would that be sufficient? Maybe fill the pipe with foam? I attached a diagram of what I am intending to do. If not, any other ideas?

 

[Woodonglass]

This should be of interest...http://www.yachtsurvey.com/fueltank.htm

 

[piperca]

Thank you. I read it, but it doesn't really pertain to my setup. His example is setting the tank on a flat deck. The more I think about it, the more I want to foam the tanks in and be done with it.

 

[rickryder]

Things to consider... How many gallons are the tanks? 7.2 lbs per gallon for fuel..... what is the crush weight of schedule 40 pipe... will they withstand the pounding transmitted through the hull when underway? Just something to think about. Solid plastic strips would be a better choice.... adhere with 5200 to tanks bottoms

 

[Mikeopsycho]

From what I understand neoprene is OK to use in direct contact with aluminum, rubber is not. When they say rubber, I'm not sure if they mean actual rubber made from a rubber tree or synthetic rubber. Another difference is that rubber will deform when in contact with gasoline, neoprene will not.

Although I'm not able to open your picture, I just see a blank page, I kinda like your idea of some kind of strips on the bottom, although I agree with rickryder, plastic strips of the correct thickness might be a better choice. Having said that, I'm not sure the crush factor of 1/4" neoprene would be much of an issue, but I'm no expert.

Foaming your tanks in is an approved and widely used method, but proper tank preparedness is a must. They gotta be etched, primed, and painted under the right conditions using the right paints, etc., etc.. And the foam has to be poured under ideal conditions for proper adhesion to the tank, and it could be difficult to get the small space under the tank fully foamed in without any voids.

Good luck with whatever method you decide on.

 

[piperca]

Rickryder: the tanks are 84 gallons each. They have four mounting tabs welded to the side, so that they can be mounted/hung from the top of the stringers on each side. This leaves a small gap around the tank. The pipe would not be taking the full weight of the tank, merely providing added support, and the neoprene strips would be there to take the shock of any flexing of the tank. Unfortunately, the tank does not fit the exact contour of the hull, so flat plastic strips wouldn't work, since the gap is wedge shaped. I guess I could wedge the back of the neoprene with a small strip of neoprene ... that's an idea! The consistency of the neoprene was explained to me as being similar to a car tire ... pretty stout. What type of plastic would you suggest? Most that I've seen, don't like to be glued.

Mikeopsycho: I have Alodine and alumiprep. I can paint the tanks prior to installation, but the original tank, which was 30 years old when I pulled it, had not developed any corrosion and it was foamed. I replaced the tank because I am repowering the boat to diesel and it was recommended that I replace the tanks at the same time. The tanks are mounted under the aft berth and are not in an area that gets wet. I think if I got water intrusion that far forward, I'd have bigger problems to worry about. If I were to paint them, what type of finish would you suggest?

 

[rickryder]

I would think polyethylene would work well....you could buy from here http://www.kitchensource.com/kitchen-islands/jb-pl16.htm and cut into strips or wedges....3M 5200 should stick them down well.....you could use modeling clay to gauge your thickness....just my .02

 

[piperca]

you could use modeling clay to gauge your thickness....just my .02

What an excellent idea!

I have a plastics supply store nearby. I will check with them on the polyethylene ... thank you!

 

[Mikeopsycho]

If I were to paint them, what type of finish would you suggest?

Sorry, I wish I could be of more help, but when I investigated replacing my tanks I decided to go with the method in the link Woodonglass posted, so I don't recall what type of finish was recommended. I was able to build a flat floor for my gas tank and change from V bottom to flat bottom. I went from a 120 gallon tank to about 100 gallons.

As for my water tank I changed from a true V tank to a modified version with a 9" flat area on the bottom. I put a small flat base to set the tank on with 5200 and plastic strips, and also put some plastic and neoprene strips between the tank and the hull. I didn't lose much volume with this tank, which was originally 35 gallons.

Incidentally, both these tanks were badly pitted and leaking aluminum, and both were unpainted and foamed in. On the upside, they were 35 years old when I realized I had to replace them. Both new tanks are also aluminum.

 

[zool]

por15 is a good choice, its moisture cured, and great for damp locations, I used the silver on mine after Alodyne and its holding up solid, even being stepped on regularly....the procedure is in the early part of my resto in my sig if u want to see the results... also reattached the neoprene strips the factory used on the sides and bottom.

 

[piperca]

Very nice! So, you didn't use primer under the por15? My tanks are 36 x 32 x 21 (roughly). How much finish do you think I'll need? I was thinking I only need to paint from the top of the stringers/tabs, down to the hull.

 

[zool]

Very nice! So, you didn't use primer under the por15? My tanks are 36 x 32 x 21 (roughly). How much finish do you think I'll need? I was thinking I only need to paint from the top of the stringers/tabs, down to the hull.

You don't need a primer, the alumiprep etches it, and the Alodyne primes it. Just clean off the grime with dawn and warm water, then use a surface cleaner to decontaminate it, then grind out any pits or craters, then decontaminate again,, then fill and fair the pits with jb weld, then put on the Alumiprep with a spray bottle, wipe it down, then rinse a few times with water to remove the phosphoric acid, wipe again with the surface cleaner (kleens-all or any automotive dewaxer/degreaser), then rag apply the Alodyne, till its all golden. Then just brush on the por15 with a foam brush, like a varnish, from the dry edge into the wet edge. About a quart will do both tanks probably. I used under a quart for my large tank, 2 coats.

around pg 7 of my build has it all...

http://forums.iboats.com/boat-resto...80sf-engine-swap-restoration-pics-598307.html

 

[piperca]

Thanks, Zool!

The tanks are new, so the prep work will be minimal. I'll let you know how this works out.

Cheers!

 

[zool]

Youre quite welcome and we like to be "let know" with pics

I suggest you still use a surface cleaner, por15 has marine clean, but any brand will do......good luck, and I firmly believe in coating an aluminum tank, new or not..

 

[piperca]

I will certainly post pics.

The alumiprep is a cleaner; do you think I require something additional?

 

[zool]

I will certainly post pics.

The alumiprep is a cleaner; do you think I require something additional?

The alumiprep is a phosphoric acid cleaner/etcher...yes, but it needs to be complete rinsed off with water before the Alodyne goes on, if your water is clean, you can probably skip the wax/grease remover, just don't touch the surface with bare hands until its painted., por5 sticks to the alodyne like glue.

good luck

 

[piperca]

Thanks, Zool!

 

[tpenfield]

I am wondering if there were tanks in the boat previously and if so, how were they installed?

 

[piperca]

The previous tank was one 140 gallon tank, which needed to be cut to be removed from below the deck. The tank was foamed into place between the stringers. The tank was rectangular with a flat bottom. The foam filled the V of the hull below the tank. I removed all of the foam and had two tanks made to replace the one, so I could get the tanks into the boat, without removing the deck.

 

[tpenfield]

One thing to consider is that a foamed in tank adds a fair amount of strength to the hull. If you install new tanks without foam, there will be less strength. It is hard to stay if the remaining strength of the structure will be sufficient.

Also, the 80 gallon tanks will be fairly heavy, as was the 140 gallon tank, and the mounting tabs may not be sufficient to hold the tank down without experiencing metal fatigue. So, from a structural integrity standpoint, just some things to consider versus the original build of the boat.