TOPIC: Relocation of gas tank in Herters

I have been restoring a 58 Herters flying fish. I've thought about using a 15 gallon fuel cell instead of the portable tanks. I assumed I would put it in the back but after seeing the recent post of the Herters owned by Haynes fiberglass sinking after resto I'm thinking the front would be better for weight balance. I'm not a boat guy so my question is, do the outboards have enough of a fuel pump on them to pull gas through 14 feet of hose? My motor is a Mercury 400 from 1961. Thanks

I dont think it would be a problem for the fuel pump. Depending on where you run the hose (floor level, or under gunwale) the fuel pump gets hep- either by gravity, or the siphon action of the hose once the bulb is pumped up.

The tank has the pickup in the top. I thought I would run the hose under the gunwale to the splashwell and then to the bulb and motor. It never will be much lower than the motor except inside the tank itself. The floor is wide open in this boat so I think it would be in the way if I ran it down low.?????

flyingfish wrote:

The tank has the pickup in the top. I thought I would run the hose under the gunwale to the splashwell and then to the bulb and motor. It never will be much lower than the motor except inside the tank itself. The floor is wide open in this boat so I think it would be in the way if I ran it down low.?????

That's why it won't be any problem.. the fuel pump doesn't have to pull the fuel a great height. The bulb will get it started, and the pump and siphon action will keep it flowing.

Even if you run the hose 100' in the air... and drop it down to the engine, the fuel pump only needs enough suction to compensate for the difference in elevation between the level of gas in the tank and the fuel pump.

See Drawing:
A= Difference in Gas level and Fuel Pump Height, As gas is spent, this level changes, but the effect is minimal.
B= Siphon-action remains neutral over this distance, The fuel pump does not have to move the fuel here.

***NOTE: if the tank is located ABOVE the level of the fuel pump, you wouldn't even need the pump- as gravity would do the work. You don't really want this in a boat (or vehicle).. because of safety. If something went wrong- fuel would continue to flow, posing a serious danger.

Excellent writeup w/illustration. The only time the pump would be required to pump the height of A plus B is when the line has run dry, and has to be pumped ovhe height of the gunwale.

Help; Does anyone know of a boat manufacturer called "Delaney"? I had one and I'd love to have pictures of it.

I have a 12 gallon or so tank in the bow of my 1957 Thompson 16'-7" Sea Lancer and have never had a problem with fuel flow to the motor. The fuel line runs under the inwale on the port side.

Andreas

Fantastic information, thanks a lot. The drawing is great.

What about venting, to keep fumes from gatheing up under the deck if it is a bow tank?

old guy

My two cents

perminatly mount the tank and add a remote fill which would be vented, just a matter of running two lines fill/vent.


I have seen old Johnson steel fuel tanks pop inwards because of the suction from the pump when not vented properly.

Plus one more cent

Run copper tube not pipe for fuel line.

Here is the plan, I have a plastic tank from a old Dodge Dakota I'm going to use. It has all of the fittings and a fuel level float in it. Just need a gauge for the dash. It is going as far up front as I can get it. I can use the fuel neck to locate in the top deck for filling and it also has a vent that will vent to the outside. For fuel line I'm using a stainless mesh with plastic coating that most of the hot rod shops sell. I am going to use 2 original Mercury gas tanks mounted in the back empty and sealed up to aid in floatation. This makes it look very original and helps the weight distribution in a tail heavy boat.

As with any modifications made there is always a plus and minus.

Plus vented, remote fill, fuel gauge and lots more room.

Minus you have just changed how boat will perform, depending on how far forward and how much fuel is in it will dictate if it will plane and how much power will be used/needed to get on plane.

I'm just wondering about the fuel vapors gathering under the deck. You know most of the boats that have built in tanks in the rear have those vents on the gunwales? one facing forward and the other facing rearward to aid in the movement of air and removal of fumes. At least that is what I think they are used for.

oldguy

Let me start off with what the requirements for a permanent fuel tank on a boat are (when i said requirements I mean the rules manufacturers are required by law to follow) The tank must be capable of withstanding a fire for 2 1/2 minutes. Will your Dodge Dakota tank meet that? most automotive tanks won't.

Tanks installed in the forward half of a boat are subject o much higher accelerations, pounding, slamming etc than a tank in the aft half of the boat. If you were buying a marine tank to put in, the tank manufacturer would have to certify that it met the USCG requirements for tanks installed in the forward half of the boat.

Tanks must be vented to the open atmosphere. That means the vent line has to go to the outside surface of the boat.

The fuel fill also has to be placed so that any spill will not go into the boat.

Fuel hose has to be USCG Type A or B. I recommend Type A. It's easier to find and will meet the 2 1/2 minute fire test. B does not but may be used from the tank to where it connects with line for the outboard.

Do not use copper. It is subject to cracking from vibration and corrodes easily. If you use metal use copper nickel or nickel copper, or steel, all which will survive much better in a boat.

If there is any electrical equipment where you are putting the tank then the space must be ventilated to the atmosphere. Either 15 square inches of open area for each cubic foot of space, or use cowls and ducting of at least three inches in diameter each.

You will need an adapter to connect the fuel lines from the tank to the fuel line for your outboard. Most places that sell outboards or service them can sell you one.

Last but not least, this is not law, but as was said, you may be upsetting the balance of the boat. Most outboard planing hull boats are designed to have the center of gravity as far aft as possible when the boat is on a plane. This reduces the resistance and reduces the tendency to porpoise. By shifting weight forward you may be actually slowing the boat and increasing its tendency to porpoise. You can try this out by running the boat with portable tanks and putting some weight to simulate the tank in the bow. Gasoline weighs about 6 pounds per gallon. Use enough to simulate the weight of the full tank.

In addition, as you use gas the bow will get lighter shifting the CG aft. So this is something you need to consider.

I think the tank would be better off nearer the middle of the boat or after near the transom. (also shortens the length of fuel hose.)

For info on fuel systems see newboatbuilders.com/pages/fuel.html

Thanks for all of the information. Like I said I'm venting to the outside and it will have a top deck fill. I will use the proper hose and connections. I can't believe the Dakota tank will fair any better or worse than a plastic tank sold at Walmart. The weight balance is a legitimate concern that I will experiment with. Thanks again.

I bought a bow tank off of craigslist that came out of another boat, so it should be Coast Guard approved. But it appears there is more to consider then "just slapping it in." I might try the weight test before I do anything to see how she handles. First in line though I need to get a outboard. That was my winter project, was to put the bow tank in, but it is hard to find all the right information/requirments needed to do it sucessfully. Meaning, without blowing your boat up! It was one of those things or ideas that looked good on paper. I know if you dig around and ask enough questions the info needed will show up eventually, or at least in this case, someone will point you in the right direction.

Thanks for all the tips.

Oldguy