Advice for Diesel Tank(s)

[Cheechako]

I would likely go plastic. But A boat I had had a pinhole leak in the bottom in both tanks. The next owner pulled the aluminum tanks and had new bottoms welded on. Evidently it was just the bottom that was bad.

[Va2shp]

Two thanks is a good idea, but I have a weird feeling about your filling scenario.

Good luck

[SpaceRnglr]

Thanks everyone for the good advice on tanks. My original question was actually about the plumbing around the tank and specifically the schematics I included in my original post (included here again). Does anyone have any advice on either of the two options I am considering. Sorry if I didn't make myself clear enough in the first post...

[Seadoc777]

I carry 120 gal of bio diesel. I switched from petroleum diesel five years ago to get rid of the smell. Bio can be hard to find I get mine in Marathon Florida at $3 per gallon. I have a 41’ ketch burning one gallon per hour at 2500 rpm - fill ups are infrequent. Sometimes I am asked if I’m baking cookies? The French fry story is slightly true. Try it you’ll like it.

[suenodelmar]

Some aluminum airplanes have what are called "wet wings," that is, there are no separate fuel tanks inserted into the wings, rather, there are sections of the aluminum wings devoted to fuel storage. When one of these sections begins to leak, it is a big problem, obviously. I understand that there are companies that will cut an access hole, or use an existing access hole, to spray a rubberized coating on the inside of that section of the wing, thereby creating a sealed "tank" once again.

I wonder whether this process would work for an aluminum or stainless steel tank in a boat. For that matter, there are a number of makers of rubberized sealing compounds in spray cans. Also, there are liquid rubber or vinyl compounds that are designed for dipping the handles of hand tools like pliers. These compounds are much thicker thean the spray can compounds. I wonder whether a paint sprayer, either airless or air pot type, equipped with an appropriate nozzle would spray the sealing compounds in all sections of a tank.

Of course, careful cleaning and etching would be required before spraying. For aluminum, a product called Alumabrite or distilled vinegar might be sufficient. For stainless-steel, a pre-painting etching compound may be needed.

Existing internal baffles might complicate the coating process. A spray nozzle with a wide spray pattern, and located on the end of a flexible tube, might suffice. If the tank cannot be easily removed, filling the tank with the sealing compound and then removing the excess may be a cheaper solution than removing the tank and installing a new-built tank.

Perhaps other members might know more about internal sealing compound materials and processes.

[Maka]

Keep in mind that each fuel tank is required to have a separate fuel fill on the deck.
So I'm told.

[Terra Nova]

Replace the tanks with welded aluminum. Provide separate fills, vents, supply and return lines for each tank, valved appropriately. Provide cleanout/s at the top of each tank. If accessible, provide drain sump/valve at the bottom of each tank. Provide a dipstick or valved sight gage at each tank.

[oldjags]

There are some liquid products that are designed to seal pinhole leaks in gas tanks. But I'm not sure how well they work on aluminum tanks or with diesel fuel, so some research would be necessary.

One of my old Jags had problems with flaking rust inside the tanks, and a pin-hole leak in one of them, and I used a product from Eastwood to seal it. It seemed to work fine.

https://www.eastwood.com/gas-tank-se...nk-sealer.html

The product description says it works with aluminum tanks and also with diesel.

POR-15 also has a product designed to seal fuel tanks.

[turtleofdart]

If there were a choice between water or diesel or lead, I would have lead lower than water and water lower than diesel. diesel is a lot lighter...I'm considering converting a 25 litre plastic jerrycan to extra diesel tank and mounting it higher than the engine making the system immune to air ingress. Our current integral keel box tank (steel Boat) suffers from condensation and associated crap....and I would rather fill it with lead and have the diesel higher up.... all this is pretty shitty work... good luck with it.

[Mike Banks]

Firstly, I do not like diesel tanks in the bilges or built into the keel. They are difficult to get at and bilge water slopping around them leads to differential aeration corrosion--such as you have just experienced in your stainless steel tanks.

Water tanks are OK down there--because if they do develop a leak it is not such a problem. My preference for diesel tankage is lift-out slab tanks locked down into frames mounted alongside the hull, clear of the bilges, and easily removed for cleaning. A tank approximately six feel long by eight inches wide and four foot tall holds over 100 gallons imperial, and one mounted each side of the hulls gives one a good margin for long trips, without the need for extra fuel stored on decks.

[captlloyd]

Originally Posted by SpaceRnglr

Thanks everyone for the good advice on tanks. My original question was actually about the plumbing around the tank and specifically the schematics I included in my original post (included here again). Does anyone have any advice on either of the two options I am considering. Sorry if I didn't make myself clear enough in the first post...

You made yourself clear the first time. Many of the posters on CF like to talk about everything but what the OP is asking.

[ironvalleyfab]

tie to the two tanks together and have the pickup in the tank with the highest bottom that way any water in your fuel will eventually settle into the lower tank, use the lower/smaller tank as a reserve and when you really need it you could close off the valves joining them and wash the fuel into the primary tank, I would go with option #1

[Scout 30]

Each fuel tank needs to be plumbed separately including fill, vent, pick up & return. The pick up from each tank should go to a T with a cutoff valve for each line right before the T. There needs to be easy access to the 2 cut off valves so you can switch between tanks. I would install the lift pump right after the T before the primary Racor for ease of priming the filter & motor. The return line should also run to a T with cut off valves after it. You must return to whatever tank you are drawing from. I would also install dual Racors with a pressure gauge.

You are smart to replace the tanks while you have access to them. I also think converting one of the water tanks to diesel makes sense. Sailboats are really motor boats with sails.

[Lodesman]

How about a third option?
I see your plans as being somewhat backwards. The large tank should be storage, and the smaller tank in use (day tank). Leave the fill arrangement to fill the 180L tank. Reverse the pump in your middle diagram to fill the 80L tank from the 180L tank, and run the 80L tank to the Racor/engine. You'd have to put the fuel return line back to the 80L tank and I recommend a separate vent for it.

[SpaceRnglr]

Thanks for the good feedback on plumbing. Actually I would like to run dual fuel lines to the engine as described by Scout 30, but I don't have space for all the necessary fittings and pumps where I need them to be. Same problem with Loadesman's advice, it is very difficult to get fuel lines from the smaller tank back to the engine. That is why I was thinking just a simple connection from the smaller tank to the bigger one would work best.

Actually, all this has me thinking... The best place in the boat for fuel tanks is under the aft bunks. I have the original manufacturing drawing and this is where they were originally shown, but they were scratched out and moved to the current location (I believe at the factory). I am tempted to install 2 larger tanks in that location as it would allow plenty of space for the dual fuel lines to the engine.

My only issue is that the holding tank and water heater are located under the bed. I think I could install a holding tank where the fuel tank was located, my only concern being it would be shaped like a pancake and that might make it hard to suck out all the poo.

Argh - why is it that all boat project start as a "let me just have a peak under the diesel tank" and now have me contemplating having 3 new tanks made, changing every diesel fitting on the boat, changing all the low pressure water system, reinstalling the hot water heater, and replacing all of the toilet piping...

Most alarming, I got a quote from a local aluminum fab shop that makes small boats and they want US$2,600 for a not-very-complicated 190 liter tank! What does BOAT stand for again, I think I forgot...