Fueling Dual Tanks

On my new to me Mainship Pilot II I have two diesel tanks that hold about 85 gallons each. The tanks are connected by a 1/2 inch maybe 3/4 inch crossover line with shutoff valves. Both tanks have their own fill. The diesel pump at the dock pumps much faster than the tanks can equalize through the crossover line. I'm curious how those with this setup handles filling their tanks.

Fill each tank through their individual/separate inlets.

Yes, fill each through the deck tanks.

The cross over is for you to run either or both engines off both or either of the tanks. Usually for when one tank is much lower than the other (say after extensive generator use).

Unless you want to get every drop possible in both tanks, fill each one individually and don't worry about the crossover. Only a relatively small amount of fuel will move from the more full tank in the time it takes to fill up the other.

If you want both tanks as full as possible, close the crossover valve until you've filled up.

Ken

Close the transfer valves for refueling, especially to top off completely. Is this a single engine boat?

EDIT: Like he says!

Yes it's a single engine. I brought it with the tanks about 3/4 full. I thought i'd need to fill the tanks separately.

I haven't read this whole thread, so forgive me. If you have a way to transfer fuel from tank to tank just pump one tank to the other, close the crossover, and "top off" the "empty" tank. Voila!

I've got four fuel tanks (and one engine). Fill them individually. Use a pump once purposed to filter fuel, but find more useful for transferring fuel among tanks.

Tamrow said:

Yes it's a single engine. I brought it with the tanks about 3/4 full. I thought i'd need to fill the tanks separately.

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I have a 34 ft boat, with single 120hp Lehman, and two 400Litre tanks, (i.e. approx 100 US gal, I think), one each side. We seldom, (in fact never), have had the tanks completely full, and never needed to, and unless you plan long distance travel early on, you won't either. The need to have them completely full to stop condensation issues etc is largely over -played & just not an issue, and less bad than having full tanks with progressively more stale diesel that is never used, in my view.

Ours are linked by a simple T junction, and the tanks drain from the bottom, so I never isolate the tanks as it stops any sludge from building up to draw from both equally, and keeps the boat in trim. Because we don't even try to completely fill, if you take is a bit slower, you can just fill from the nearest (i.e. dock) side filler, and let the natural equalisation take care of the re-distribution and therefore trim. Works for us, and my fuel lines are the same as yours in diameter.

Fuel Feed and X-over Lesson Learned

I close the crossover when I fill. After one fueling I decided to run off just the port tank and closed the stb tank feed. Left the fuel dock and headed out with full tanks.

After about 1/4 mile, as I passed the coast guard station off my port side, I heard someone yell. Actually don't think they were yelling at me, but I looked over the stb side and noticed fuel streaming from the stb tank vent. Quickly stopped, opened the x-over and stb feed. The injector pump fuel return is plumbed to both tanks and, without the x-over and feed from the stb tank, was overfilling it. I was leaving a small sheen in my wake.

Very lucky to have discharged so little and not been cited! Never did get around to putting a tank selector on the return line.

Jamie

markpierce said:

Fill each tank through their individual/separate inlets.

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Of course.

I open both deck fills and fill each tank individually. Opening the deck fill on the opposite side seems to help the venting. I have tried to clean the vents but i am not sure how successful I was. I wonder if the crossover line which has a low point behind and below the transmision might be clogged as well. The fuel gage is erratic- wired to just one tank.