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boatnut
06-23-2015, 09:35 AM
A while back I posted a thread about how we left gas in the tank of our 18 for close to 10 years of non-use, the result was a thick layer of a pitch like substance on the bottom of the tank which could only be resolved by changing the tank. The 18 is a 1969, so after 46 years based on the corrosion issues with tanks mounted in foam the tank replacement was likely needed. For your information, we took the tank out (Father's Day project). The tank had almost no corrosion. The foam was all intact and showed no signs of being saturated. The tank was difficult to remove due to the good shape of the foam and its adhesion to the tank. So for what ever it is worth, this is an example of a tank that survived 46 years of an incorrect mounting process and remained in good shape --only to be torpedoed by leaving gas in it for too long. Attached are a few pics including the tank we had built at Moeller Marine, they offered the best price to manufacture and ship the tank to California. They were also excellent to work with. The new tank is also sealed with an epoxy coating (per George Carter's advice). Ed

gcarter
06-23-2015, 10:03 AM
Nice looking new tank Ed.
You can see in the picture of the bottom of the old tank, there are clearly visible "water lines" showing.
So clearly, sometime in the past it had been sitting in saturated foam. I bet it took years to dry out.
Well done, and I'm sure the new tank will give a lot of confidence.

Morgan's Cloud
06-23-2015, 10:25 AM
Unfortunately what happened to you is exactly what my brother went through. In the end , the old galvanized tank was in like new condition , inside and out , but that tar like goo just wouldn't budge , and the carb sure didn't like it either .

It's a shame that the original tanks weren't epoxied first though . You can foam that sucker back in and forget it just about forever .

Scott Pearson
06-23-2015, 12:20 PM
George,
I don't think that's a water line. I think that's a bend in the tank to fit the "V" in the hull. Look at the new tank and its the same.

boatnut
06-23-2015, 05:30 PM
George,
I don't think that's a water line. I think that's a bend in the tank to fit the "V" in the hull. Look at the new tank and its the same.

That is a bend Scott. I cannot see a waterline on the tank or any signs in the foam of it being saturated. I think the drain tube along the bottom vee in this boat was installed and sealed better than most. I will be putting a pvc pipe under the tank sealed with epoxy. I am not sure what percentage of tanks have corroded either to the point of leakage or close to leakage -- but this one was OK. This boat has also always been in a pretty dry climate, not sure if low humidity helps this. Any way it is one data point.

mattyboy
06-24-2015, 10:29 AM
that tanks days were numbered the rust on the seam is where they fail and today's fuels will kill the lining on all the hoses not to mention that they will blast all the old crude off the inside.

now you have piece of mind all the new lines hoses and fittings are able to stand up to the new fuel and the tank will last another 45 yrs also you are not going to gunk up the new motor. plus your boat is now legal as far as USCG standards are concerned.

f_inscreenname
06-24-2015, 11:14 AM
This is why you donít foam in an aluminum tank.

http://i21.photobucket.com/albums/b264/f_inscreenname/9_2.jpg

This is from a Donzi I did last year. Not a boat you want a failed fuel tank install in.
This was a mid-west boat (fresh water). Tank was less than 10 years old. The whole thing was coated in coal tar. Then put in place and foamed in. The issue was the front bow eye leaked (another impossible thing to fix in a Donzi without taking the top off). Water rolled down the drain and over the floatation foam and on top of the tank. Between it and condensation the coal tar was pulled off the tank by the foam and then the tank was turned into swiss cheese because the tank could not breathe (air circulate around it) or expand and contract.

http://i21.photobucket.com/albums/b264/f_inscreenname/3_6.jpg

The new install is done like my 1972 Allmand SuperNova was done (43 years later and the tank is as good as the day it was made, I had it out 2 years ago just for inspection). Cut up rubber strips (I used a couple found tractor trailer mud flaps) for it to sit on and for the sides between it and the stringers so there is an air space and itís not sitting on fiberglass anywhere. Liquid nail the strips in place and a couple more dabs on top of the rubber. Squeeze tank in place and then block it in with some teak blocks and stainless steel screws. The tank is there to stay and the way itís installed even though this boat is on its 3rd tank it should be its last for a least a few decades.

gcarter
06-24-2015, 02:26 PM
I concur the foam in the smaller boats is a problem. It being there is counter productive.
Doing what you did in a 22C w/a 6' long tank holding 500# of gasoline is a problem IMHO.
Imagine 10 G's, or over 5000# impacting rubber strips that don't exactly conform to the tank can
be a an issue for tank structural integrity.
I do think it's fine for smaller tanks though.

gcarter
06-26-2015, 09:45 AM
I discovered I need to clarify the above post.
The foam I was referring to was the flotation foam in the hull and that boats w/it might not drain normally in the foredeck area.
I firmly believe in mounting the belly tanks in foam. It's the best support system there is.
I believe if a tank is "PROPERLY" sanded and coated, it'll externally last almost indefinitely.