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Fuel system capacity on a 25 Bert with a single inline is a challenge. I will need to run 2 outboard saddle tanks. The question is, can I common the tanks and avoid constantly swapping tanks to maintain balance?

The diagram is what I am wanting to do, is there a reason this would not work?



Thanks in advance for the feed back.

Scott, is there any way you could bore holes in the stringers and run a crossover pipe connecting the two tanks at the bottem so they equalize them selves and only run one fill, feed and return. Your diagram looks like it would work but you will need two fills to insure there are no air locks and both tanks fill to the top.

RussP

Wouldn't the vents keep the tanks from air locking? I was hoping the single fill & Tee would fill both tanks equally at the same time? If one tank fills first, shouldn't the filling fuel divert directly into the secound tank?

Would the engine pick-up / feed lines keep the tanks at the same level?

I might be able to add a lower combining/cross-over hose connection, but I was hoping to avoid tank penetrations and fittings at the bottom of the tanks (leaks). I do like the idea of 1 pick up and 1 return line coming from one tank, that simplifies things. That would make the plumbing much easier.

I don't think there is an issue (USCG) will low tank pick-ups with diesel, I know you can't have any penetration on the bottom or sides of a gas tank, top only. I could feed the engine from the low cross-over hose as well.

I was under the impression you could not have any penetration on any fuel tank below the top. Could be wrong...but would be alot of fuel in the bilge if crossover line took a dump...whether from rock'en and rolling or someones foot or hand being in the wrong spot.

My last boat was a single with twin outboard tanks...other then two fills your layout looks similar.

You might be right with fuel siphoning to the low tank thru pickups...always figured they just drew together evenly as most tank fill ups where within a couple gallons of each other.

Scot,
I've never seen two tanks plumbed with T's to feed a single source balance themselves. Theres always one that that feeds just that much easier and returns just that much easier.

Russ's suggestion with a crossover hose is the only real way of making sure you acheive equal balance of tanks. That way you also only need one feed and return.

Also T'ing a fuel feed even with the tanks vented mostly leads to fuel backup in the line before both are full.

FEDERAL LAW -- USCG

183.518 - Fuel tank openings

Each opening into the fuel tank must be at or above the topmost surface of the tank.

Fuel tank openings refer to holes into which fittings may be installed or fuel lines attached. Fuel tank fill, fuel tank vent, fuel distribution, fuel tank sounding, and fuel level sender fitting accesses are examples of such openings. If the attachment fitting is welded or attached by other non-removable means to the fuel tank, the opening is considered at the top of the attachment.

Scott,
Patrick just beat me to the CFR on fuel tanks, also ABYC standards say that each tank has to have its own un-interupted fuel supply fill, hose and vent line, either A-1 USCG approved hose or B1, B2 hose and clamps must be 1/2" wide on the hoses. Fuel fills must be clearly marked for the type of fuel(gas or diesel).

Whats the date of those regs and are they across the board or deal with charter apps because a good many of the larger yachts I've ever been on have sight tubes on the tanks and crossover pipes.

I did a ton of floscan installs so I saw a lot of tanks.

And does it deal with new boats as the one Scot is doing is not a new boat but a refit or repair so to speak. The reg is not retro active.

ABYC standards is nothing but a money con game.

I was always uner the impression the regs were different for gas vs diesel, and that a diesel tank could have a low / bottom withdrawl. I know ever commercial vessel out there has bottom / side withdrawls and sight glasses...as Bruce mentioned.

So what up with that?

33 CFR 183.518 - Fuel tank openings is dated as Dec 2005...

OEM equipment and associations prior to that date may be excluded by a grand father clause, but any new installation that was not done before that date, either by the OEM or other contractor, will be obliged to conform.

Kind of like open bilges below engines with limber holes that connect to the common bilge can remain as such if everything is original, but if major refitting has been done, those limber holes must be blocked off so that oil can not reach the bilge pumps.

New tanks done after 12/05 would have to conform to 33 CFR 183.518.

While one could ignore the reg and build in a base cross over, it could be a problem on an insurance survey, purchase survey, or a USCG inspection...

If the cross over can be done in such a way that it's a fixed, non removable system, (welded, glassed, no hose connectors or clamps, etc), it will probably qualify as "top of the tank". However doing that, with a rigid connection, will take some engineering to allow for flexing of the boat without eventually fatiguing the cross over.

scot wrote:I was always uner the impression the regs were different for gas vs diesel, and that a diesel tank could have a low / bottom withdrawl. I know every commercial vessel out there has bottom / side withdrawls and sight glasses...as Bruce mentioned.

So what up with that?

The newest reg states only fuel tank and makes no distinction between different types of fuel...

Also the regs can be different between commercial craft and pleasure craft. 183.518 pertains to pleasure craft.

A cross over isn't going to need to be large diameter, 3/8" - 1/2" I.D. will work fine. Maybe use copper tubing, formed into a coil to compensate for boat movement. Weld flanges to the tanks and silver solder the copper into the flanges after the tanks are installed. A 55% - 60% silver content solder is high strength and can be used to marry dissimilar metals such as copper, brass, aluminum, and stainless steel.

Another thought would be a section of flexible LPG pigtail, that once wrenched into the connections are then silver soldered to become an "non-removable" fixture.

Thanks for all the feed back guys.

I think I will go with the common withdrawl and common return, and 1 fill hose for each tank, and see how it goes. They should either equalize, or the engine should pull on each tank "somewhat" evenly. Keeping the fuel lines the same lenght and the pick-up tubes and locations the same should help the system feed evenly.

The worst thing that can happen is that I have to turn a couple of valves ever few hours, if they don't draw down evenly. Or worst yet....the tanks don't pull down together and the fuel return pumps raw fuel out of one of the vents! Hopefully that can't happen.

A few runs and refills should tell the tale. I will attempt to locate the fuel manifold in an easy to reach spot, just in case.

Thanks again, good brain food.

The returns...an interesting dilemma. I forgot about those.

I would think a crossover on top of tank, but below vents would take care of blowing fuel out the vents or overfilling one tank.

scot dont think it will help but dont forget i still have my old tank if you need it

Thanks Matt,

I think that would be more work than building new, based on my space requirements. I have to admit I spent a bunch of time pondering it!