Building a custom fuel tank?

[tnelsmn]

I'm building a custom fuel tank for my Hydrostream project. Plan on building it out of 1/8" 5052 aluminum. I've built some custom fuel cells in the past, but nothing marine. My main question is should I set up the fuel feed with a dip tube, or add a threaded fitting at the bottom of the tank? I'm planning to use 1/2" NPT weld on fitting for all the ports; feed, return, vent, possibly a drain, etc. Unless you feel I need bigger. Power is a 2.0 175 for now, plans on an EFI 2.5 in the future. Here's my cardboard mock up of how it will fit in the hull. My math puts it around 26 gal. Open to input, thanks!

[wogi]

If it was me, I would not feed from the bottom, I would use a dip tube from the top in the reaer of the tank. On a bottom feed setup, the tank would drain into you boat if a leak should a rise in your fuel feed line, I my be wrong but I do think that cost gaurd reg. forbid a bottom pick up for that resand, Just me two cents. BTW must have a happy dog with all the Chewy boxes you have to work with LOL And nice work on the boat

[tnelsmn]

Wogi, didn't even think of a leak in a fuel line! Thank you!

PS, sadly I don't have a dog, developed quite an allergy as I've gotten older. Grabbed those out of the bin at work

[FUJIMO]

3/8'' aluminum pickup tube welded to the bottom of a 90 street elbow. cut the bottom of the pickup tube at a very slight angle, or cut it flat with a small vee cut into the center. that threads into the threaded aluminum bung you weld into the top of the tank. I would recommend making two of these pickups & welded-in bungs right next to each other at the rear low point of the tank at center. they come in handy sometimes as a spare, in the future. 1 1/2 fill hose 90 near the front of the tank on top. it fills to the top this way & gas is never sitting inside the fill hose. 5/8'' vent port also nearest the front on top. this can simply begin with another welded-in threaded bung, or a prefabricated aluminum tube 90 welded to the top of the tank. You always want to provide a generous sized access round deck-plate(PYHI) over the top of your fuel connection points, both at the front and rear of the tank. its also required by coast guard if they ever look at you. keeping the fittings/bungs in a smaller pattern(but not so small you can't get a wrench on, and turn 90 degree fuel fittings right next to each other) won't negate a huge access deck-plate. don't forget an welded-in inside baffle or two. pressure test at 3 psi(no more) for ten minutes with soapy water rag or spray bottle on the outside. I have designed hundreds of aluminum marine fuel tanks. hope this helps...

[rjdubiel]

I have a good Vking stock tank if ya wanted to check it out or look at it quick.

[racervboat]

I have a good Vking stock tank if ya wanted to check it out or look at it quick.

We could turn that into a beer cooler

[rjdubiel]

We could turn that into a beer cooler

Done!!

[FUJIMO]

also just make sure u have enough room above the long tube pick-up(s) to pull them up & out of the tank. 1/8''(.125) material is good up to 75 gallons or so capacity, then go with 3/16'' after that. if dropping into a cavity, weld 4 placements of angle aluminum on the top edges to use to thru-bolt thru the stringers(no self tappers) & foam the tank(s) in place with 4 pound density a/b foam(not 2 pound)… if possible, always run a length of pvc under the center of the tank, say 3/4'', if in a cavity, to drain from forward of the forward tank transverse bulkhead to behind of the rear transverse bulkhead. you can also weld a small tab of aluminum sticking up next to the fill neck to drill a small hole in, to attach a tank static ground wire to, instead of stripping a bunch of the insulation off the end of the ground wire & stuffing it down the fill hose before you push it on the fill neck, like some do. the fuel sender placement & orientation & type is a whole nother subject.

[tnelsmn]

Fujimo, I should give some more info. Theres a large angled clearance that will be built in to clear the transom knees that will almost separate it into two halves. I was debating whether or not it would still need baffles. Maybe just one to split the front and back half? My plans is to set the lines before securing the tank in the boat. I'll be welding 1-1/2"x 1/4" aluminum angle iron along the sides of the tank and bolting it down to some to some mounts I fabricated and fiberglassed to the floor. The mounts are 3/4" plywood with 5/16"-18 T nuts secured from the bottom side. So if I ever need to access fittings and such I can just unbolt the tank and slide it forward. I don't have that great of pictures of the mounts but you can see them here near the transom. Thank you for all the advice!

Also, I checked my blueprint and found that my memory was off, the math puts the tank just shy of 23 gallons.

RJ, I may want to grab a few measurements off that.

[frank jackson]

fuel tanks are never big enough , make it as big as will fit with baffles , the weight differance does not make **** for differance ... 20 gal. in a big tank or a small tank means nothing , going long distance fill it up ... Tall is better than wide or long .

[Motv18]

The best part of build your own is putting vents where they work.

I prefer a baffle every foot from the pickup. Which you want about 2 inches off the bottom. Metal collects moisture faster then plastics