Convert water tank to fuel?

[Sean B]

Hi guys, it’s been a while since I’ve been on. I think since whatever happened that wiped out years of posts (what a bummer) Here’s my question: I’ve been trying to figure out the best way to get an extra maybe hundred gallons of fuel on board. Suddenly it occurred to me that I have this enormous 70 gallon aluminum water tank already that would easily do that job. I would add two 15-20 gallon water tanks somewhere outboard for freshwater to replace it, and actually those could be rigged with transfer pumps switched at the bridge, for those days when all the fat guys cluster on one side (to level out the weight). That last bit I’ll probably never do, but fun to think about. Anyway — has anyone ever converted that stock water tank to fuel? It’s in the cabin area of course, but we are talking about diesel, in my case. Also- hello again!

[Capn Tony]

You might want to think about adding a tank in the side wall of your cockpit . I have one built into the port side 30 gal

[h2ojst]

Hey Sean, The first thing that you'd have to look at carefully is the location of the pickup. If my memory serves me correctly, the water tank outlet is on the bottom and this is a real no-no for fuel. At the very least you would have to remove the tank and install a tube pickup in the top for USCG regs. In case of a fire burning through the pickup hose you'd be literally fueling the fire with raw diesel if left as-is.

[dougl33]

Holy crap Sean. Welcome back! I'm not sure I'd switch the water tank. I think that would be very bad for whatever small amount of resale value we left in these boats.

[Sean B]

I’m not thr least but worried about resale values and I care even less about USCG regulations, unless they actually make sense. I’ll never sell that boat, maybe it’ll be my Viking funeral boat. Except I wouldn’t want that to happen to it either. The lower pickup is something I hadn’t considered but now that I have, I would definitely change. There’s a cutout in the top for the gauge I could use, but probably would just add in/out ports on the top. Maybe use the gauge opening to get a wrench inside. A brass cap on the lower pickup tube, after I die-cut threads onto is Burlingham Coast Guard Approved. It would just be a holding tank that I would only fill or empty via transfer pumps. I could get clever with the diesel fuel return lines too, but probably would not.

[Sean B]

I’m more worried about the reports of pinhole leaks developing in the bottom of these tanks than anything else.

[h2ojst]

Pressure test everything after you're finished with the plumbing & you'll be just fine. I'd say it's better off corrosion wise with diesel fuel than water, so if it's not leaking now, chances are it won't start, just ground it well. I'd also add about 5 gallons of methanol to get rid of any water residue, then drain that out before adding your diesel.

[Sean B]

I think I’m going to skip this bright idea. The known tendency for pinholes bothers me too much, and it’s not as though I can yank that tank, have a look at the bottom, slap on some magic goo of some sort and put it back. Only place that tank can go is out and that’s a one-way trip. 70 gallons of water leaking into the bilge is one thing, but the prospect of 70 gallons of diesel doesn’t sound too great to me. If I did it, I think I’d cut out the old tank and add a new one there, but that’s not the best way to add fuel capacity either.

[dougl33]

Probably a good idea!