Old Fuel tanks?

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Oct 12, 2007
Folks with old fuel tanks , or new ones poorly/cheaply built not to be serviced might want to contemplate



Just checked out the site you noted, and seems like a really good idea.* I left the site thinking, "Why didn't I think of that?"*


Actually the cove plate should be on the inside of the tank so the fuel pushes the plate against the tank bolted thru with a solid collar on the sides.* An oval shape is best so the cover plate can fit thru and be bolted on the in side.* The holes should be high on the tank close to a corner where the tank is more rigged. The inspection hole I made was 18 X 18 just big enough more me and or/a welder to get into the tank.* Most local fabrication shops can make the cover plate and the collar.

Old tanks require regular maintenance/precaution and a back up plan in case of a leak.* First make sure your tanks are bonded to the zinc loop to prevent corrosion/rust.* I added additives that help absorb water/moisture back into the fuel. Heating the tank/fuel will help evaporate the moisture, and of course polish the fuel.* I read or somebody told me the heated the high volume return fuel *would help evaporate the moisture/water in the tank.* The old saying a happy tank is a used tank, so move that fuel around.

Maintaining the out side of the tank is important even though tanks mainly rust/corrode from the inside out but moisture water/rust on the out side will also reduce the live of the tank and may indicate a problem concern.* I ran the diesel boiler hot water hoses under the tanks to keep warm and dry and the engine room about 80 degrees.*

Since the tanks are old, I only fill them up ½ to ¾ full so if one tank does spring a leak the fuel can be transferred to the other two tanks though the fuel polisher.* If the tank could not be repaired then the old tank would be used as a frame work for several smaller tanks.* However, many/most tanks can be repaired.* Replacing with several smaller tanks would not require cutting up thro lf tank and several smaller tank could be installed with out a major disassemble of the engine room.*

Anyway, if/when a tank springs a leak I have a game plan that should not cause tumultuous problems.* So what do you do to maintain your tanks and/or your game plan.* Arent old ugly trawlers fun?* )-;*
An oval shape is best so the cover plate can fit thru and be bolted on the in side.


Hmmm... this has me a bit baffled (pardon the pun).* How do you get to the bolts if they're on the inside???
The bolts are attached to the folding ring which you feed inside the tank and point the bolts outward through the inside gasket, and then the holes in the tank. You then place the gasket and lid on the outside and bolt it down. The website shows a photo of the inner piece being fed into the tank. Since the inner ring basically folds in half, there is no need for an oval hole as mentioned earlier.

-- Edited by Carey at 16:11, 2007-10-17
Studs are welded to the collar/cover plate that is in side the tank, and the nuts are on the outside.* My point was if oval then would not have to be split.* A solid collar would make a better*seal.* The other point was if the cover plate was on the inside, instead of the collar then the pressure of the fuel would push the cover plate against the tanks rather than away from it which would make a better seal, which requires an oval.**The last point was make the hole big enough to clean, inspect and repair the entire tank, rather than multi little holes.

Been there, done that and hope not to do it again.* ****
Phil/PF is right. An oval is a great idea. Using an oval you could even have solid cover plates on the inside and the outside. Twice as good at not leaking.

He is also right that sloshing in the tank would push a solid surface tighter against the gasket and be less likely to leak.

Of course it may be overkill, but it is better.
Forgot to mention, the oval is also better if you need to get your shoulders inside of the tank.

To reach, weld, or climb in.
"There realy is no replacment for good ports on tanks that allow access to clean. Commercial guys learned this a long time ago. "

Actually if the tank is properly built to be easily cleaned of water & gunk a clean out is not necessary.Even crappy fuel from rusty drums cleans up simply in a proper tank.

The cost of a creating a proper servaceable tank is minor , and the maint takes moments , but since owners dont DEMAND serviceable tanks , the extra $50 bucks stays in the boatbuilders pocket.

With lots of boats in the $1/2 Million* buck range the absence of MONEL tanks is shocking!!


-- Edited by FF at 04:54, 2007-10-18
Now I understand (yeah, I am a slow learner)...

I like the idea of the double solid plates.* At first, that didn't make sense, either... then I realized that a minor seepage around the inner gasket could be trapped by the outer gasket.
Recently an article in PMM pointed out the problems in having mild steel tanks with fiberglass sprayed on as a coating. Leaky decks could allow water to sit on top of a tank and eventually seep under the FG- causing the tank to rust. My four tanks are coated in FG, never had teak decks, and the tops of the tanks are in excellent condition. I reinstalled 3 access ports on my rear Port tank today (1 original, 2 added recently to clean the tank) and I used a cup brush on a 4" side grinder to remove the FG from the sealing area on the tank where the added ports were (should have been done this way to start with). I am amazed at how bonded this material is to the steel tank. It took a lot of effort to clean down to bare steel. If this is bonded over the whole tank as well as the area I was working with- I think this is a big plus for these fuel tanks. Any thoughts

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