permanent fuel tank vent designs

[bob johnson]

So I want to put a permanent fuel tank in my boat that didn't have one. I have chosen the center V down the middle of the boat...the space is not that wide and it is not that deep... so I am building the tank myself...because to just get 28 gallons it needs to be 96" long!...nobody makes a tank that would fit... I have cut open a tank I had that was too pitted to use last year on another project, I can see the baffle design. I also notice that the vent tune was an aluminum tube welded in place that ran the length of the INSIDE of the tank and was tack welded to a few of the baffles to keep it in place. Is that length of run inside the tank needed?. I have looked for pictures of tanks being built and designed... and none have had that long tube...most just a hose barb welded to the tank....

secondly I found this picture of a custom BOAT tank.. and I am wondering if this is acceptable...because I could use this set up , since the tank JUST fits under the floor... until I saw this picture, I had planed to make the front of the tank where the fill tube is attached come up off the tank under the front deck... And I still may do that.....I just wonder about if this is a bad idea or an acceptable idea....seems the sloshing of the fuel might travel pretty far up the fill hose!

bob

 

[mickyryan]

can the baffles trap air? if so id run vent along entire tank with reliefs in each baffle, also think of putting air vent at highest point so its not submerged on take offs or slow downs?

 

[bob johnson]

the baffles have an opening usually at the top corners and the bottom corners and a small opening in the middle bottom and top....in a dynamic vessel like a boat, I doubt there would be any trapped air for long...this tank will be long and shallow, so the vent will for towards the bow...

 

[mickyryan]

you know its weird but I had to think about it my tank vent is at rear with fill tube the pickup is in like rear third along with sending unit .