Two Fuel Tanks

I'm thinking of changing over from one fuel tank to two wing tanks.
It's a single, petrol engined boat and the tanks would most likely be made of aluminium.
Now, I know that all connections must be on the top of the tank. So I was wondering if there's a simple way of having the two tanks filled from the one filler, as clearly you can't have a "balance tube" between the two....
Any suggestions on how best to "plumb" it all?

 

Did you already find this older thread in the archive
http://www.boatdesign.net/forums/gas-engines/whats-best-way-tie-2-fuel-tanks-together-28295.html

 

No... didn't find that one FMS... thanks....
Guess I'm just going to have to go with a ball valve at each tank outlet and draw from both, closing one or the other as need arises.....

Didn't quite get how fuel would self-level as one poster suggested though...

 

Ive never seen a crossover valve connecting gasoline tanks...with diesel its common.

 

I have three diesel fuel tanks connected to a manifold near the fuel filters. By opening more than one valve at the manifold, the tanks will self level. By opening the deck tank's valve it will fill the below decks tank selected. One thing about top pull fuel pipes, if the level is low and the boat getting tossed around by conditions, it's inevitable that the suction pipe will get a slug of air eventually and this can kill a diesel at the worst time. Gas engines may be more immune.

 

A good strategy for eliminting air suck when running low of diesel in a seaway is to build a baffle or small dam in the tank around the fuel suction.. Suck fuel from this 2 liter or so baffle and also direct the return fuel into this baffle. Naturally the baffle is not fuel tight and has limber holes, but is seems to hold just enough sloshed, return line fuel to get the job done

 

Good strategy and sounds effective. Unfortunately all my tanks are off-the-shelf units from West Marine and I cannot access the interior to make this clever modification. Thanks Michael.

 

A small 5 or 10 liter gravity fed accumulator tank also works well. Pull fuel from the accumulator. Ive got one buried in the keel stub.

 

I don't see any way to control water in the fuel tank without putting a drain in the bottom. And it must be on the bottom plate ...not on the bottom of the sides and located in the lowest corner of the tank. Unless you can pour a gallon of water into the tank and immediately remove it you don't have control. Also you should be able to put a drop of water into the tank and immediately remove it. I see no other way to do it.
I never equalize my two diesel tanks but draw off one at a time. Unless one plumbed a crossover tube from the bottom of the tank one could get air in the feed tube. Not good. But then on my non-crossover system I could get air in the infeed as well if a connection leaked (air). And if I pulled fuel off the bottom of the tank sucking air could even happen then if the fuel system on the engine was higher than the bottom of the tank, which is almost always the case. Basically leaking connections can ruin your day, year or life.

 

And, Mat-C, why do you want to change your current arrangement?

-Tom