Fuel tank questions

We have two fuel tanks in the boat, each are 100 gallons (Gas). Each have a shut off valve at the tank draw tube located on the top of the tanks, then they y into one line that runs into the engine rooms and then y's again to each of the three fuel filters and then to each of the 3 engines (gen set, two 350's). The tanks do not have a balance tube or line that connects them together besides the main common line. Tanks are aft of the mains under the rear deck.

I have tried running with each of the main tank valves full open in hopes of drawing the same amount out of each tank to keep the boat balanced. Sometimes it draws more out of the Port, sometimes not but never equal.

So for the most part now I run one tank at a time, draw it down to about 1/4 reserve and then swap tanks. Then on the next run I will reverse the starting tank so that I am not packing one old fuel for long. As one time on a long run I had each tank open but for some reason it only drew out of one tank and I ran the boat out of fuel, kind of scared me at first, but then I went and popped the hatches and seen one tank was still reading full and the other was dry.

Is this standard practice? Why don't they draw equal? I see no provisions for a balance line/tube and no other bungs in the Stainless tanks. Its not a huge deal, just makes me wonder. Each of the mains has an electric fuel pump located at the engine, so they pull the fuel.

If I was to design this boat I would have made the tanks able to balance out on their own, as I am always bumping the trim tab on one side or the other on a 4 hour run as its now 800lb lighter on that side!

Personally, with 2 engines and 2 tanks, I prefer a tank to engine setup. I'd re-plumb the valve setup so that you can select either engine to either tank and same for the generator. Then normally each engine draws from its own tank (reduces the chance of a fuel issue taking out both engines at the same time and keeps the boat more level) and the generator can be switched to either as needed.

On my own gas boat, each engine draws from its own tank, but with a crossover valve setup so you can run both engines from 1 tank. Generator has its own pickup and draws from the port tank only, no way to switch it to the stbd tank.

rslifkin said:

Personally, with 2 engines and 2 tanks, I prefer a tank to engine setup. I'd re-plumb the valve setup so that you can select either engine to either tank and same for the generator. Then normally each engine draws from its own tank (reduces the chance of a fuel issue taking out both engines at the same time and keeps the boat more level) and the generator can be switched to either as needed.

On my own gas boat, each engine draws from its own tank, but with a crossover valve setup so you can run both engines from 1 tank. Generator has its own pickup and draws from the port tank only, no way to switch it to the stbd tank.

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This is exactly what I planned on doing, just would have thought in the boats life someone would have done it by now if it did not come that way.

I planned on one line from each tank to the engine room, then a t set up with valves so you can run each off of one tank or each off of their own tank, and a line from one side to the gen set, it never gets used a lot anyhow.

I still don't know why they don't pull equally, you would think it would as each tank should see the same draw vacuum as each line is the same distance.

You say each engine has an electric fuel pump. Are they fuel injected with a return line ? Maybe only goes back to 1 tank.
Any difference in the length of lines or restriction between the 2 tanks would cause 1 to draw easier than the other and draw more from the one with less resistance.

I would have the port engine draw from the port tank, same with starboard engine and starboard tank. But have a crossover so either engine can draw from the other tank just in case of some bad gas. I would like to be able to have the genset draw from either tank. But normally each engine draw from it’s own tank.

Solly said:

You say each engine has an electric fuel pump. Are they fuel injected with a return line ? Maybe only goes back to 1 tank.
Any difference in the length of lines or restriction between the 2 tanks would cause 1 to draw easier than the other and draw more from the one with less resistance.

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I'm pretty sure his gassers are carbed, which would generally mean no return lines.