Replacing original black iron tank

[Tayana42]

Petar, I concluded that the tank leak I had developed because my boat has a slight list to starboard. The leak was in the starboard tank. Water (even a little) may have settled on that side under the tank or at the edge of the tank and remained there causing the iron or the weld to rust at a seam. In your case are you certain that there isn’t water or leaked fuel laying against the outside of the tank? That might impact how you approach your repair.

I did not try to epoxy or weld the tank. I don’t know if that would have worked or have been cheaper. This wasn’t visible until after cutting open the top of the tank to begin the work. I would have deep reservations about welding the tank in place. Certainly it would be an option if you could remove the tank to have it welded but that is the problem with so many boats which have the interior constructed or engine placed after the tanks are put in. I hope you find a good solution that works for you.

[phorvati]

Originally Posted by Tayana42

Petar, I concluded that the tank leak I had developed because my boat has a slight list to starboard. The leak was in the starboard tank. Water (even a little) may have settled on that side under the tank or at the edge of the tank and remained there causing the iron or the weld to rust at a seam. In your case are you certain that there isn’t water or leaked fuel laying against the outside of the tank? That might impact how you approach your repair.

I did not try to epoxy or weld the tank. I don’t know if that would have worked or have been cheaper. This wasn’t visible until after cutting open the top of the tank to begin the work. I would have deep reservations about welding the tank in place. Certainly it would be an option if you could remove the tank to have it welded but that is the problem with so many boats which have the interior constructed or engine placed after the tanks are put in. I hope you find a good solution that works for you.

Thanks, for me I know well the history behind all of my issues. PO (two POs ago) had a near mayday experience as he described in this sail magazine article. https://www.sailmagazine.com/cruisin...day-that-wasnt
Looks like he has removed the photo in 2017 from the article.

So my guess is that aluminum diesel tank, stainless holding tank, all three water tanks and the big iron diesel tank all deteriorated as a result of salt water soaking the tabbing around those tanks. Well, they were probably deteriorating, and this finished them off for good. This is why its not a good idea to glass in metal object into the hull, whatever they may be chainplates, tanks etc. And regardless if they are 316 aluminum or whatever(i guess with the exception of fiberglass tanks) . Stagnant oxygen depleted water will ruin aluminum or 316SS.
Also all the shitty(undersized) engine mounts were all but dead. I replaced the mounts, last PO replaced the water tanks, I converted to composing head and added two new smaller aluminum diesel tanks, and this is the last relic that needs to be replaced. From that article I learned why none of the electronics was working (lightning).

[phorvati]

So I cut the tank open and got rid of the baffle. I also ground out the inside. Nasty job it was. I got in touch with ATL and I'm going to send them the inside measures. I'm getting the ATL supercell because it collapses a bit more. Gives me a better chance to insert the bladder without issues. I'm going to order either neoprene or buena-n rubber to line the inside. Maybe 1/8" so I can do that while they are quoting me and making the bladder.
He was talking about the need to vent bc this material permeates. That's not what I wanted to hear. My wife already calls the boat "musty" even without permiating diesel tank. How bad is the permiating odor? What size hose/fan to use. Should i kist drill somw holes in a far end so that when fan sucks it has a chance to have good airflow? It would be nice if a 12v pc cooling fan will do as I already have some for composing head. So I can have the same spare. Does fan need to be ignition protected? I'd like to think it doesn't bc it's diesel.

I think I will weld the piece I cut off back. It will keep the bladder snug. I still have that large inspection port.

[Scubaseas]

Nice work. Might be better to leave the cut out as a removable piece. Makes it easier to get the bladder in or to service the tank at a later date if needed. Weld some tabs on top and tap the tank for machine screws. Just make sure the screws are short enough not to hit the bladder.

[mvweebles]

For others, I repaired a 50g steel tank with epoxy and some fiberglass fabric. Lasted about 10-years. My belief is the dissimilar materials eventually work loose at the edges and will fail. There are apparently some liquid paint-like liner formulations used in the small aircraft industry, but they work best when the tank is out and can be rolled around to spread the coating.

On my current boat, I too had a pair of 225g saddle tanks (450g total). I replaced each 225g tank with two 110g fiberglass tanks. Plastic is forever.


Peter

[Tayana42]

Petar, nice work opening up the tank. Yes grinding out the baffles is a nasty job. As far as permeation I have had none. No issues at all. You asked about ventilation before and I said yes I have a vent. I thought you were asking about a tank vent, I didn’t realize you were asking about ventilation of odors around the tank. No, I don’t have any provisions for ventilation around the tank. There has been no need, no permeation at all. I don’t know about the supercell material, I think mine was not that. I didn’t have any trouble getting it inside of the old tank. It was flexible enough.

By the way, the access I cut in the top of my tank is about 12” x 18”. I covered it with a piece of plywood set into a simple frame so it doesn’t slide off and with a finger hole so I can lift it off easily. I lined the iron tank with dry deck tiles and finished the cut edges of the iron tank with vinyl trim for a car door edge protector.

[phorvati]

Originally Posted by Scubaseas

Nice work. Might be better to leave the cut out as a removable piece. Makes it easier to get the bladder in or to service the tank at a later date if needed. Weld some tabs on top and tap the tank for machine screws. Just make sure the screws are short enough not to hit the bladder.

I'll just tack weld it after I have the bladder in and before I add the rigid foam inside. I think I need to specify where the oval opening is in my drawing so that they can add the opening to insert internal cell pieces.

[phorvati]

So I got a quote and it was 6k. That's absurd. I don't think I'll be doing a bladder. Any other places to get a quote? It was 900$ just to draw the plan. And it appears my tank is not 250gal. It's closer to 120gal.
Petar

[Scubaseas]

https://www.readycontainment.com/pro...fuel-bladders/

https://www.imtra.com/products/other...2fDiesel+Tanks

https://fuelsafe.com/marine-fuel-bladders/

[phorvati]

Originally Posted by Scubaseas

https://www.readycontainment.com/pro...fuel-bladders/

https://www.imtra.com/products/other...2fDiesel+Tanks

https://fuelsafe.com/marine-fuel-bladders/

Does anyone know what prevents installing the bladder inside the iron tank enclosure below deck?
I went through this standard but there is no mention on bladders.
https://www.uscgboating.org/assets/1...YC.1002.01.pdf
ATL installation guide specifies that you must provide enclosure
"Each bladder must be installed within a fully supporting (load bearing) container or smooth structural “nacelle”. ALL surfaces of the bladder must be CONTINUOUSLY supported. Special attention should be placed on providing full rigid support to bladders of unusual configurations; i.e. bladders designed with inside corners, sumps, pass-throughs etc."
I'm thinking i could modify the shape of my iron tank to comply supporting standard bladder which would be reasonable priced.

[Scubaseas]

Also look at ABYC H33 Diesel Fuel Systems

You would want a bladder inside a metal tank to meet the 2.5 minute fore standard. You can use foam (see above standard for weights, etc.) to fill any spaces between bladder and metal tank.

[phorvati]

Originally Posted by Scubaseas

Also look at ABYC H33 Diesel Fuel Systems

You would want a bladder inside a metal tank to meet the 2.5 minute fore standard. You can use foam (see above standard for weights, etc.) to fill any spaces between bladder and metal tank.

So based on what i'm reading, I'm thinking about doing the following:
1. Clean the inside of the tank, and fix holes with some diesel rated sealant

2. Line bottom and part of the sides with those plastic tiles to keep moisture away from bladder.
3. install bladder and fill with air fully, making sure no kinks and creases.

4. Route the fittings where i need them to go.

5. Tack weld the cover back but leave inspection port open.
6. Pour 6lbs 2 part closed cell polyurethane foam like this one

https://www.amazon.com/TotalBoat-Ure.../dp/B01AAWRYX8
all around to fill voids between fully inflated bladder and the rest of the steel tank. I just have to make sure foam does not attach or damage the bladder.

7. Place inspection port to let foam cure in the shape of the tank.


That would seem to satisfy H-33 requirements. my old tank is 1/4" steel. I also don't have to worry about straps etc. as tank is now fully enclosed and supported.

There is a 100 gal bladder that I am considering that appears to fit the inside of my tank with some room on the top for fittings.

[Scubaseas]

Seal rust holes with epoxy paste/putty, paint inside with POR15 or similar and top coat to prevent rust.

I'd would use a heavily waxed 2" or 3" PVC pipe and pour foam to form a cove shape for the corners. Covering the pipe and form in wax paper also works. Make a form up with something like two 2X6s in a 90* angle and screw pipe onto these. Block off one end. Then pour measured amount of foam in to make a cove shaped bar. If you need to fill flat voids just use sheet XPS or Urethane foam board glued onto the tank with a urethane sealant/adhesive like liquid nails or even use silicone or epoxy. Lay down some 3/8" or 1/2" XPS or Urethane foam board to make sure any old welds for the baffles are not a wear point. You can glue the cove piece in with low volume rattle can spray foam if you want to bond it to the sheets and be able to easily sand the cove to sheet joint smooth.

Using the bladder as a form may not work as the foam may generate more pressure than the bladder can overcome. Plus you ideally want to make it so you could remove the bladder at some point, Expanding Foam sticks quite tenaciously to everything.

I'd still mechanically attach the old tank top but if you have to weld it, insert tank, deflate and put some wet blankets between bladder and tank when you tack weld it back in place and hope you don't get splatter burning a hole.

[Scubaseas]

Urethane Foam , Expanding Marine Polyurethane Foam

Frequently Asked Questions - General

The 16lb stuff is easy to hand sand. The 80lb stuff is almost like softwood. Their Partall Wax works well. US Composites has been great to work with. No affiliation but have used them for years for supplies.

[Bill Seal]

Is there any magic caulking that can be applied to the inside of a fuel tank? Or am I looking for unobtainium or baloneyum?
If I just give up and decide to cut the tank into small enough pieces to get through the "Engine Dungeon" hatch, has anybody here used an angle grinder, air chisel or sawsall?