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**HappyMdRSailor** · 24-03-2016, 05:16

UGH!

Revisiting my long overdue fuel tank scrub and access plate manufacture/install.... Upon initial cleaning I've discovered the dreaded "pits"!

It's only on the bottom of the tank, and probably in the neighborhood of 5% overall... Unfortunately, the pictures revealed deeper pitting than I thought, so doing nothing seems stupid...

I've successfully coated tanks before, but herein lies the problem... This sucker is big, and can't be removed, rotated, i.e. impossible to fully coat... I'd love to be able to simply coat the bottom... BUT... I'm concerned that a coating edge inside a diesel tank is begging for coating failure...

To compound the problem, I'll bet there's some pretty good flexing in the tank bottom...

After a few thread research moments, I came upon two recommended products by minaret, but contacting the first they say "must be fully coated"
Product 1
https://www.kbs-coatings.com/tank-sealers.html

Product 2
I haven't called yet...
POR-15 Fuel Tank Repair Kit

Of course I could just pour in 20 gallons of epoxy and call it a day !

Any thoughts my brethren???

**a64pilot** · 24-03-2016, 05:38

I'd use aircraft fuel tank sealer, aircraft wings have been used as fuel tanks for lord knows how long, wings are of course full of holes, rivets hold the things together, only thing that keeps the fuel in the wings is the sealer, and wings flex too, so the sealer has to be flexible and adhere well over dozens of years.
But then I'm used to the stuff too. It ain't cheap though and I'd use the A version of the stuff as it's thinner, about like 5200. The B version is thicker, about like silicone caulk.
Metal has to be absolutely free of any oils though, we use Acetone for that

witzgall · 24-03-2016, 05:45

We had this happen to our fuel tank. Some of the holes had actually perforated through, and I think yours look to be close to that point.

I would have a new bottom put on by a welder. Here is a video that I made.

https://vimeo.com/68139929

Chris

captjcook · 24-03-2016, 06:00

I guess making a fixture to tumble your whole boat is out of the question?

I put this in the category of things I was glad I found but not happy to see...sorry it happened to you...

I have used POR (Paint Over Rust) products...they work well and I recommend their products. POR-15 is great on steel. They certainly have a smell to be avoided...unfortunately I have only done a motorcycle tank with their tank coating...it worked.
IIRC KBS carried POR.

If it were my boat, I would cut out the tank and replace with two if possible...just always wondering in the back of my mind if the coating will fail, making a mess at the worst possible time (anytime).

A bladder might be the answer after coating the bottom.

My friend's weld shop long ago stopped doubling fuel tanks. It takes almost half the time of building a new one, then there is liability. Just not the right thing to do.

I truly wish you the best of luck!

Jim

Sent from my iPad using Cruisers Sailing Forum

**GordMay** · 24-03-2016, 06:11

Quote:

Originally Posted by a64pilot

I'd use aircraft fuel tank sealer ...
... and I'd use the A version of the stuff as it's thinner, about like 5200. The B version is thicker, about like silicone caulk ...

Can you recommend any particular brand/product?
ie ➥ https://www.aircraftspruce.ca/menus/...ksealants.html

**HappyMdRSailor** · 24-03-2016, 06:29

Quote:

Originally Posted by a64pilot

I'd use aircraft fuel tank sealer, aircraft wings have been used as fuel tanks for lord knows how long, wings are of course full of holes, rivets hold the things together, only thing that keeps the fuel in the wings is the sealer, and wings flex too, so the sealer has to be flexible and adhere well over dozens of years.
But then I'm used to the stuff too. It ain't cheap though and I'd use the A version of the stuff as it's thinner, about like 5200. The B version is thicker, about like silicone caulk.
Metal has to be absolutely free of any oils though, we use Acetone for that

I was hoping you'd chime in here with your expertise!
Spectacular Idea... My main concern now being trapped corrosion even if I get the application site clean... I suppose a conversion coat preceding?

Cool paper here:
http://www.vansairforce.net/articles/tank_sealant.pdf

**HappyMdRSailor** · 24-03-2016, 06:38

Quote:

Originally Posted by witzgall

We had this happen to our fuel tank. Some of the holes had actually perforated through, and I think yours look to be close to that point.

I would have a new bottom put on by a welder. Here is a video that I made.

Chris

Chris...

I would LOVE TO.... but the tank is about 24x48x60 trapezoidal "coffin" shaped...

Quote:

Originally Posted by captjcook

I guess making a fixture to tumble your whole boat is out of the question?

I put this in the category of things I was glad I found but not happy to see...sorry it happened to you...

I have used POR (Paint Over Rust) products...they work well and I recommend their products. POR-15 is great on steel. They certainly have a smell to be avoided...unfortunately I have only done a motorcycle tank with their tank coating...it worked.
IIRC KBS carried POR.

If it were my boat, I would cut out the tank and replace with two if possible...just always wondering in the back of my mind if the coating will fail, making a mess at the worst possible time (anytime).

A bladder might be the answer after coating the bottom.

My friend's weld shop long ago stopped doubling fuel tanks. It takes almost half the time of building a new one, then there is liability. Just not the right thing to do.

I truly wish you the best of luck!

Jim

Sent from my iPad using Cruisers Sailing Forum

Jim...

Maybe a well planned knockdown???

Yes, I think some POR product is part of the procedure... I've used them and like them... Bladder is a last resort, but not undoable...

**HappyMdRSailor** · 24-03-2016, 06:45

Quote:

Originally Posted by GordMay

Can you recommend any particular brand/product?
ie ➥ https://www.aircraftspruce.ca/menus/...ksealants.html

Melikes this?
https://www.aircraftspruce.ca/pages/...nts/ac2362.php

Rhapsody-NS27 · 24-03-2016, 07:13

Quote:

Originally Posted by HappyMdRSailor

Melikes this?
https://www.aircraftspruce.ca/pages/...nts/ac2362.php

Wow, $63/pint seems steep to me, but I'm not familiar with them. I wonder what kind of coverage you get on this product.

Another sealant product on that site is $126/pint and $252/quart.

Aside from tank sealers, I've had to remove my leaky fuel tank that was installed in the keel and now looking at putting in a fiberglass/vinylester tank and have been looking at tank sealer/liners for my project as well. I've also considered the KBS and POR products.

UNCIVILIZED · 24-03-2016, 07:30

Some tanks are purpose built fiberglass, with metal liners. Take your pick metal wise.
The fiberglass is the part which is fully responsible for holding the fuel in place. Though bonding to stainless is no panacea. But then again, if it's fully encased in glass, the bonds needn't be perfect.
Plus, if it's a "fiberglass" tank, then bonding stiffeners to the outside, is easier than me typing this response.

NOTE: That if you plan to go this route, epoxy would be the better option, for the bonding aspects.

**a64pilot** · 24-03-2016, 07:39

I think any aircraft fuel tank sealer is essentially the same.
We used a different brand in the Military and use one made by Flamemaster I think where I work now and I can't tell any difference.
Need to know it comes as either A or B. A is thinner and B is much thicker, like if you wanted to apply it to the sides of a tank, you would use the B.

Then it comes from 1/2 to 2. those numbers equate to the pot life of the product in hours.
For coating the bottom of a fuel tank, I would want A2 myself, thinner and I'd want the longer pot life. You can paint it on with a stiff brush, think of it like 5200, it is very similar in consistency and just like 5200 one drop will ruin clothes, car seats and I'm sure any fabric cushions.
When it's wet acetone will remove it and even though your not supposed to I have thinned it out with acetone and had it work well, just like I have thinned epoxy with alcohol, and I'm sure your not supposed to do that either.
Lowes sells a painters wipe that will remove both 5200 and fuel tank sealant, amazing little wipes they work.
Once it's dry as far as I have seen nothing in the world will remove it, it has to be physically removed by scraping, etc.
It will stick to itself very well as long as there is no oil or something on the old, so if for instance you ran out you could order more and paint right over the old without having to do anything to make it adhere, no sanding or anything.

It is a chemical cure like epoxy, it does not cure by drying like some paints, so even a thick layer will completely cure without shrinking or anything, so I'd start out by making sure the pits were filled, then painting a layer over the rest of the tank, I'd make sure I got the corners well and maybe even an inch or two of the sides, Idea being to ensure any water never touched the metal again.

I'd definitely order the can, the tubes are meant for a special mixing machine and go into a special type of caulking gun. It's two part, usually a pure black and a pure white that you mix together to make a grey. Easy to mix by color alone when you know the proper color, many people like to mix it "hot" meaning more of the dark to shorten cure time, of course this means you run out earlier as there is no extra and I feel sure by mixing it in the incorrect ratio it wont work as well.
It's a lot like mixing resin, except it won't cook off like resin will if you have too much in a container.

**a64pilot** · 24-03-2016, 07:48

When figuring out how much you need, how to apply it etc., think of it exactly like 5200, there may be some difference in thickness, but it is a lot like 5200 so far as working with it.

UNCIVILIZED · 24-03-2016, 07:51

Where are the baffles located in this tank? Assuming that it has some. Which, it'd be loco not to, given that it holds 320 gallons.
And the reason I'm asking, is that, where they are & their orientation & size; both governs, AND rules out some of the possible fixes.

**a64pilot** · 24-03-2016, 07:54

Looking at the Aircraft spruce link Gord gave, I'd stick to the pro-seal or 3M brand and stay away from the sloshing stuff, I think that is what we call Monkey blood, is meant to fix leaks, and I have not had good luck with that stuff, idea is you slosh it over the cured sealant and it gets into the cracks and crevices and seals leaks, great idea if it worked.