Broken fuel tank mounts on Lund SS

[snowman48047]

I need some help here. Replacing rotted flooring and ALL the foam on this boat. Floor and foam is out. My problem; all 6 of my fuel tank mounts are broken. The tank itself seems to have shifted toward the stern roughly 1/2". Based on the pics it also "dropped" maybe 3/16". The tank is plastic and has nuts embedded in it. My problem is the top of the tank is not perpendicular to the stringers. It is at an angle maybe 5 to 15 degrees, depending on location. I was planning on using 5056 aluminum angle bracket at 1/4" thick to replace them but the angle is going to be a problem. I don't want to stress the new brackets for the start. What else might I do?

 

[budski]

Your idea sounds good to me, I don't think it will stress it to much is there any way you can move the back forward and maybe shim it at the rear first.

 

[Scott Danforth]

I would just get new mounts, foam in the tank and drop in the floor

the existing mounts broke on the bend line from fatigue. that means your tank was moving around

 

[snowman48047]

Yes moving the tank back into original position is easy. I am trying to find something to put between the tank and bulkheads to keep it from sliding around. The factory brackets are junk.

I'm not putting the 2 part foam back in. That crap absorbs water.

 

[fishrdan]

Plastic fuel tanks will "grow" when exposed to fuel, so you want to leave room for expansion. When I replaced the fuel tank in my Crestliner I made some blocks to keep the tank from shifting around. Half the thickness of the block was ABS plastic and the other half was closed cell foam (cheap WalMart exercise pad) which allowed room for the tank to grow. As I remember, the tanks will grow about 3%, which is a LOT in a 4' long tank. The blocks I made had 1+" of closed cell foam , so the tank could squash the foam as it grew.

I made ABS plastic sheets from ABS pipe, cut a slit in it, place in the over until it flattened out, then pressed flat until it cooled, cheap plastic sheets. Cut up the sheets to make a stack of them to form a block, then glued them together with acetone.

I wouldn't use angle aluminum for the brackets, too rigid. I'd make them out of sheet aluminum, and make a radius bend (3/4" to 1" radius). A radius bend would be less susceptible to breaking like the old brackets, and allow you to easily bend the bracket to the tank's angle.

There are probably foam tape strips underneath the tank, 4-5 per side the entire length of the tank. Completely compressed by now I would imagine and probably the reason the tank is sitting lower.

 

[fishin98]

I would make new brackets out of the same material and thickness. Clean the bottom of the tank and the area that it sits on and use 3M5200 to help it stay in place. Just my 2cts

 

[fishrdan]

5200 won't stick to plastic fuel tanks....

 

[fishin98]

5200 won't stick to plastic fuel tanks....

Interesting! Experience?

 

[fishrdan]

Experience?

Yep, tried, it won't work, though I was trying to seal a pin hole.

Almost nothing sticks to the poly-whatever plastic fuel tanks are made from, then add in the plastic leaching through fuel vapors that will react with 5200...

 

[Woodonglass]

I'd HIGHLY recommend you consider using some kind of flotation foam in your boat. Lot's of guys have used the Pink/Blue slab foam from the Big Box stores. Cut it and pack it in as best you can. It will NEVER absorb water,and if any puncture gets in your hull you'll be glad you did it.

 

[snowman48047]

Well I dug out 600lbs of wet foam. I was stunned that NONE of it stuck to the aluminum. I will be packing in as much blue foam as I can as I have a source for FREE scrap. I had the 1/4" aluminum fuel tank brackets made up and they are perfect. Plenty of room for the tank to expand but it isn't going to move anymore. Still working on it....what rivets do I need for the 3/4" deck?