A question of tanks, and I am sure I know the answer but...

[bobfnbw]

Greetings all.

Recently pulled the 75 gal. aluminum diesel tank located deep in the bilge under the engine out. I suspected a leak, but found a cratering of the aluminum which is 0.125" and H5052 al. The craters are across the bottom and up the sides, there are multiple holes from 1mm up to several cm. This is a common problem with endeavours or any boat that has tanks that sit in bilge water.

Others have repaired the tanks using marine-tex then glassed over it.
I intended to do just that, and have pressure washed the tank and cleaned it up with a wire wheel. I also have a ~40 gal water tank that is at the sand blasters now, intending to do the same.
The diesel tank I was going to use red-Kote to seal it from inside as well, and permaflex for the water tank. Then marine tex to the craters, then glass over with cloth and resin, then epoxy paint the exterior, and use 2"x2" HDPE on the bottom of the tank, epoxied to the tank so water can't get in between it and the tank. I figured that this would last at least as long as the original tank, which was 23 years or so.

Now the question is:

Is this the best idea, or should I just replace it with a new aluminum tank?
A new tank would be $1000 USD. The smaller water tank almost as much.
This money of course could be used for the multiple other projects I have for this boat.

So what would you do?

Thanks in advance, Bob

[skipmac]

A few years back I ran over a piece of pipe in a boat yard that popped up and poked a good sized hole in the car's gas tank. Was getting ready to leave on a cruise so crawled under the car with a wire brush and some marine tex to do a quicky temporary repair, intending to replace the tank when I returned. Sold the car four years later with the temporary patch still on.

Think I would try the marine tex repair at least on the diesel tank. Not sure if I would use it on the water tank. Epoxy is made from epichlorohydrin and bisphenol-A. Epi is really toxic and probably not recommended for potable water systems. Plus it might taste bad.

[Celestialsailor]

Seems like a lot of work with possibly mixed results. Have you tried Ronco tanks to see if they have a replacement? Their prices are very reasonable. I have used them for years.
Ronco Plastics - www.ronco-plastics.com

[bobfnbw]

The other water tanks were replaced with ronco tanks. Great company, unfortunatly they do not make diesel tanks, and their is not a size to fit this area.

The potable water tank will be lined with PermaFlex - Commercial / Industrial Floor Coating, Basement Waterproofing System
which is ok with potable water. The marine tex will not touch the water.
The major trouble is already done. Getting the tanks out was a b@%$#. But the rest will be easy.

But 1500 bucks will buy half my ports (new found metals stainless ports) or most of a new inverter, and half the price of a rewire. So.... I really don't want to do this again in 2 years, but one other on the endeavour fourm did this repair with excellent results for over 10 years. Just wondering if anyone else had to do something like this.
My gut tells me to get the new tanks. But my wallet says.. hold on there not so fast.....

[Talbot]

I had a new diesel tank custom made for me in UK from thick plastic. These were accurate to less than a millimetre on the form that I made up from scrap wood, so knew that not only they would fit in the hole, but I could also get them into the hole!

These plastic tanks are also suitable for water - Tek Tanks.

[westsail42]

If you plan on keeping the boat for a long time, I would replace the tanks.

[Celestialsailor]

Originally Posted by westsail42

If you plan on keeping the boat for a long time, I would replace the tanks.

I really agree with this statement especially if you are going to leave your home port for any length of time. It can be very expensive when someone knows they have you over a barrel for a repair or re-manufacturing of a tank.

[Cheechako]

Can you have the holes welded? Long term, cruising far and wide: replace, Local cruising live aboard: try the repair. I suppose it all depends on how hard it was to get out!

[delmarrey]

How much is your labor and materials worth in relation to the cost of a new tank?

And if it sits in water, I'd go plastic.

[Celestialsailor]

Another option which come to mind is fiberglass tanks. I don't know if you are into the adventure of making them or not but look at the advantages...
1)Impervious to corrosion
2)Cheeeeeeeap!!! Relative to $1000 a tank

Just a thought

[thinwater]

but epoxy is not going to stick to HDPE. Little does.

And if you epoxy/glass the bottom and ups the sides, several layers, it will not matter that it is in the water.

[westsail42]

Yes, virtually NOTHING (in the usual arsenal of adhesives)sticks to HDPE.

Something as important as a fuel tank, especially if it is hard to get to, is not something I would fell comfortable "patching".

Buy the best, cry once.

[perchance]

Can you not cut the bottom out and have a new one rewelded into it?

[thinwater]

I can assure you that many tanks with this sort of damage are repaired and go on to last another 20 years. There are several things you need to answer:

1. Is the repair resin rated for this? Red-cote seems to be.
2. Is the surface prepared? Short of sand blasting inside the tank (yes, I have done this) I am skeptical.
3. Is there enough structural metal remaining? If the pitting is isolated (say, less than 15% of the area) it is not a concern, and a few layers of glass will reinforce any weak areas.
4. Have we stopped the corrosion? Yes, inside and out.

One question is adhering the coatings to aluminum; normally a surface pre-treatment is required, but I am not experienced in that area - research it. I believe West System may have info on-line.

Of course, the other question is always the cost of a new tank.

I have a 15-year old frp tank in my boat that I built myself. Any shape is possible.

[captjcook]

You have gone to a lot of trouble to remove the tank, IMHO I would consider the what if of your repair leaking, after being slammed in a seaway, then you start pumping diesel into the waterway and it cost you $10,000. The weld shop I use builds aluminum marine tanks for approx. $7/gal would normally use 3/16 thick for a 75 gal fuel tank. you could then glass the bottom (with proper prep) to protect from bilge water and never worry about it. If a surveyor found the repair that you are talking about it would surely be a dealbreaker in selling in addition to looking at everything else under a microscope. Spend the $525.