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Old 02-21-2021, 01:04 PM   #21
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An alternate method to paper towels is baking powder. Sprinkle under the tank. It changes colour to off-white with diesel - very sensitive.

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Old 02-22-2021, 03:19 PM   #22
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If you find your tank is in fact leaking, don't forget to include your insurance company. If it is a result of corrosion, they won't be responsible for buying you a new tank but they probably will pay to have it removed to find out. I also had this issue. The mechanic removed the tank to find out after 3 tests it didn't leak. It almost has to be a leaking fuel line. Diesel tanks do not have the check valve that gas tanks have and a leaking line will keep leaking due to syphoning. So make absolutely sure it's the tank before you extract it!

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Old 02-22-2021, 03:27 PM   #23
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Paul - thanks for the suggestion. However, I purchased the boat last Sept with the suspected leak listed on the survey and the insurance company had the survey, too.

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Old 02-22-2021, 03:31 PM   #24
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Tank Leak

It leaks diesel, but not air, not Dyed water.
Put it under pressure, disconnected all the lines.
But fill it with diesel, and it leaks. Soooooo
my next attack will be to sand blast the inside of the tank, and apply
a coating to the interior. Working through 8 inch holes is just thrilling!

Ill keep ya'll posted on how it works out.
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Old 02-22-2021, 05:30 PM   #25
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I just went through this, although I didn't bother to find out exactly where my tank was leaking, other than to make sure that it wasn't leaking at a fitting that could be repaired. The look of William's tank is the same as mine and probably the same construction. Fiberglass over steel. Apparently the idea was that the layer of fiberglass would keep the exterior from rusting and the diesel would keep the insides from rusting. Seems to work for about 40 years.

My tanks are so close to the hull that I could barely get my fingers underneath. But were I could, I could tell that the thin layer of fiberglass had delaminated. If I pushed up, the layer would oilcan and leak out somewhere, although the tank itself was sufficiently stiff that it didn't flex. This would squirt out the diesel in the fiberglass "blister." It might then take a day or two to fill the blister back up with diesel from the pinhole leak in the tank. No leaking for two days and then leaking again. Grrrr. It would also have been possible to pressure test the tank and have any bubbles or leakage hidden under the veneer of fiberglass.

I didn't have inspection ports in mine and felt that this was a project for a professional, or at least somebody with experience. If I had already had three 8" inspection ports, one in each tank section, I might have tried coating it myself. The only remaining difficulty in a DIY job is cleaning out the tank. I hired a guy who had a steam cleaner, a wet shop vacuum, and a helper. He ran them all at once and cleaned out the tank in about 30 minutes. Best part of that was he hauled the goop (and there will be goop) off to the hazmat site. That was included and took some of the sting out of the $2,800 price tag.

Since the entire bottom and up the sides 6" was coated, I don't know and don't care where the hole was. That reminds me of the scariest part. Before he put in the coating he whanged on the bottom of the tank with a steel marlinspike. He said that there was no point to coating a tank that he could punch through. My tank passed the test.

Now the question is do I bite the bullet and have the other tank done?

Good luck.
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Old 02-22-2021, 07:52 PM   #26
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I would not cut the hull sides to remove a fiberglass tank. If the tank can't be sealed from the inside, cut the tank up to remove it in pieces. Replace with a tank or tanks that can fit through the engine room access points. But it should be possible to fiberglass the inside of the tank. Work through your existing access ports or cut a larger portion of the tank out to give you room to work inside the tank, then glass it back in after you have glassed the inside of the tank. The existing tank has structural strength, you just need to seal it with a layer of resin and cloth if it is, in fact, delaminating. Cut the side of the tank out to see what's going on. Fiberglass can always be repaired.
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Old 02-22-2021, 08:03 PM   #27
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If the tank is steel covered with fiberglass, the method that I used to repair my black iron fuel tank may be of interest. You can see it on my Youtube channel at:
I re-filled the tank this winter and no leaks.
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Old 02-22-2021, 10:15 PM   #28
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I totally agree with "fgarriso" assessment that you can not pressure test a a delaminated fiberglass tank!
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Old 02-22-2021, 11:00 PM   #29
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2800 sounds cheap
Iím probably 700 in, and 40 hours of labor so far. Wish I could find someone to do it around here.
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Old 02-23-2021, 11:44 AM   #30
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Since you already have inspection ports installed, I wonder if somebody has attempted to address the problem in the past. While it is possible to put in inspection ports just for a look-see, most wait until there is an issue. You may find a failed patch job.

I was very fortunate in that my tanks were empty enough so that I could pump the leaking one into the other using the fuel polishing system (which took hours). I suspect that the tanks had not been completely full for years and I had recently filled them. It may be that I had put more pressure on the tank than it had seen for years.

Once the inspection holes were cut it was possible to put a light in and check out the condition of the tank. The bottom panel was rusty, but the sides and baffles all appeared to be perfect. The bottom plate had way more corrosion, which made me wonder if it had been constructed of a different alloy or grade. There wasn't a lot of gunk, but the 3 or less gallons of diesel remaining would have both gunk and metal shavings in it. I didn't think it was worth saving.

Pressure cleaning removed the scale and left shiny metal in some places. A steel marlinspike was used to whang on the bottom and make sure that it was solid enough to coat. If not, it was possible to reinforce the epoxy putty with steel or aluminum mesh if the area was small, but that wasn't required. I peeled back some of the fiberglass on the bottom of the tank and whanged on that from the inside. It didn't make any pimples on the outside, so it was structurally okay. But somewhere there was a pinhole leak.

One man mixed part A with B in baseball size gobs while the other applied it by hand, smearing it over the surface at 1/8 to 1/4" thick. The sides of the tank were only done up about 6 inches, as that's where the corrosion stopped completely. My prior owner had moved the fuel fills on deck because he said that water sat on them (I don't know why he didn't put in scuppers right there). So it was very likely that water had sat on the fills and if (when) the o-rings were not perfect, a lot of water would have entered over the years.
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Old 02-23-2021, 12:08 PM   #31
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Thanks!
All you input has been very helpful.
I’m kinda worried about the thickness of splash zone
It looks like it may be hard to work to a quarter inch.
I was thinking epoxy paint? Not sure, may get some splash zone to try it.
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Old 02-23-2021, 12:35 PM   #32
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Great posts Glauko and Marco !

One thing concerns me is the surface preparation of the rusty bottom. How does one garrantee a good bond between the coating and the old surface?

From industrial practice I would want to abrasive blast the surface, but this is impractical (dry ice blasting?).

Also, I have seen other coatings (non epoxy) offered for, say, aircraft tanks. Are you using epoxy becasue it is readily available?

My fear is that the fuel gets behind the epoxy.

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Old 02-23-2021, 12:36 PM   #33
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Been there, done that. 4 years and $12k ago. Our steel tanks looked like that, with the fiberglass sheath and inspection port. Sawed them out. Had new tanks made to a smaller capacity. Slipped 'em right in...
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Old 02-23-2021, 12:40 PM   #34
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The consistency was about like peanut butter. If I was to try it (and I might), I would think about using a notched trowel to get the right amount on. Follow it with a Japanese style finishing trowel to smooth everything out. A corner trowel would also be handy. I think that the person mixing would have a hard time keeping up.
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Old 02-23-2021, 01:09 PM   #35
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Quote:
Originally Posted by Nick F View Post
One thing concerns me is the surface preparation of the rusty bottom. How does one garrantee a good bond between the coating and the old surface?

My fear is that the fuel gets behind the epoxy.
My concern as well. The tank was cleaned with a pressure washer using a citrus soap and then rinsed. I couldn't detect any residue from the diesel and I really looked close. What was odd at first was that the tank wasn't allowed to dry out. Splash Zone is made to be used underwater (even mixed underwater) and adheres to a wet surface. If there was a speck of diesel left and the epoxy didn't bond completely it would still seal. It's one of those things that can be agonized over in theory but is safe and sound in practice.

One of the "tricks" that we came up with concerned keeping the fuel line exit fitting clean. My guy was wadding up a paper towel just right in order to goop around the fitting but not get any into the fitting. I just happened to have some wool daubers on board. Put one in the fitting, goop up the area, and gently pull it out with a twist. Took 10 seconds for a perfect finish.

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Old 02-23-2021, 10:34 PM   #36
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It is available, but it’s consistency may be easier to apply, like with a brush and roller. Not sure which way to go. I am going to blast the tank with crushed glass to clean it and rough it up for whichever coating I choose.
Thanks for your input. All are great things to ponder!
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Old 02-24-2021, 04:53 AM   #37
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Wow -

Glass blasting sounds like an effective process, but how do you keep glass from getting all over the boat and especially into the engine?

Have you considered dry ice blasting? I have no experience with this but it looks interesting.

One comment: after blasting a steel surface, the coating should be applied as quickly as possible - preferably within hours. Steel blasted to white metal develops mild rust extremely quickly.

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Old 02-24-2021, 07:23 AM   #38
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Here’s a thread about sealing the inside of tanks using FlameMaster 3204. I’ve used the stuff and it works.

https://www.trawlerforum.com/forums/...ting-3719.html
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Old 02-24-2021, 08:26 AM   #39
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To the OP:
I'm curious but must have missed it - what is the tank material?
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Old 02-25-2021, 01:05 PM   #40
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Here's how I solved a similar issue on my aluminum tank. I used ProSeal, a tank sealant designed for aviation use in integral tanks with gasoline of jet fuel. This was 3 1/2 years ago and all is well.

https://www.trawlerforum.com/forums/...ant-36019.html
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