Fuel tank vents

I have 2 "poly-cube" fuel tanks on my boat.They are portable, 15 gallons ea. Poly cubes are pretty much just heavy duty general purpose tanks, not your standard fuel tanks. Very popular up here for folks making long runs up rivers where they need added fuel capacity. Anyway, they use standard 55 gallon drum style, plastic bung caps. They aren't vented and the other day I went on a pretty long run in the boat and noticed the sides of the tank were sucking in from the vacuum. I know this could cause problems, but I can't for the life of me find any vented caps for the tanks. Any idea where I can find a cap that would allow for ventilation without letting water in? <br />Thanks- Steve<br /><br />By the way, the Attwood vents for sale here at the Iboats Mall are what I will probably go with, if they will keep out the water. Unless you guys can think of a replacement cap? Any suggestions?

Re: Fuel tank vents

SteveinAK,<br /><br />I have just done a bit of research on tank vents when putting in a permanent tank in my boat. The attwood (and other) brand vents are designed to go in the deck or hull of the boat with a vent hose connectecting the two. A loop in the hose or a rise in the hose above the vent location prevents water from running back into the the tank. The vents themselvs do not prevent water from passing through. There is one exception, and again it is a thru hull design that will still require you to add a fitting to the tank to attach a hose to. <br /><br /> <br /><br />I think your best bet is to add a small closable vent to the caps like the portable tanks have. That way you open it when needed, and seal it to prevent water intrusion.

Re: Fuel tank vents

A vent on a cap will work but make sure that you will not fill the tank up to the point that the fuel level will be up near or higher than the vent. I'm not able to see your tank so I'm not sure if this will happen or not...<br /><br />Also consider the sloshing around of the fuel.. It will escape out if it has the chance... But if it's a "portable" tank that has some open space "air" left in it when full, you should be ok...