gas tank vent

I am enclosing the gas tank on my new boat under a rear deck. I am concerned about fumes and want to vent the tank. I have looked at vents and am thinking of getting this one - https://greatlakesskipper.com/produ...ine-attwood-90-degree-boat-gas-tank-vent.html
The info suggests making an anti-siphon loop in the vent line. Has anyone done this and do you have any advice or suggestions on venting gas tanks? My boat is a Tracker Grizzly 1448. I have room behind the back seat for a 6 gal tank on one side and the starting battery on the other with room to spare. I know from my last project that gas fumes will be present. I just want to be careful, particularly with the battery in there.

BTW, Great Lakes Skipper has lots of stuff and some pretty good prices. I have ordered from them before and have had good service and delivery.

Unless I missed something are you going to hook this to your tank or just to the compartment where your tank is?If just to the compartment, your going to have to move the air somehow.I don't believe it will go out the vent.Maybe if you had some kind of little scoop to push air in & than it would come out vent.

You can purchase gas fills with the vent built in.

Otherwise, if you are just wanting to vent the deck like crazyman said, I would get the scoop style and install one facing forward and one aft.

If I'm not mistaken, boats with built-in gas tanks have either a vented fill or a separate vent line (or both?). From what I've read, a vent line is supposed to run from the tank to some point forward and as high as possible on the boat to prevent water from getting in the line. The actual vent is through the hull and on the outside away from the interior of the boat. Apparently the air moving past the vent creates a vacuum and the fumes are sucked out or the higher pressure inside the tank pushes the fumes out. Here are a couple of illustrations I found from an old Popular Mechanics or some such magazine.





As I said earlier, I'm not sure about any of this but am trying to find out whether anyone has run a vent. I want to get the fumes out from inside the deck to outside of the boat. I could just lift the deck lid and vent it that way but hoped for a little better solution. I also know from my last boat that the fumes build up under the cover so there is always a smell of gas inside.

I can't see the pics that you posted (firewall).

What kind of tank are you venting? One that is made to be enclosed or your run of the mill portable tank? I have a single 12 gal. tank mounted underneath my rear deck that is constructed to be a built in. The only vent that it has is the one incorporated into the filler neck that is mounted on the transom. I have no fume problems whatsoever but I also have a narrow area immediatley forward of the transom that is not completely sealed off from the bilge.

For a sealed deck/bilge, a vented filler neck along with the scoop vents mounted on either side of the deck to vent the bilge should be all that you need. They vent the bilge (or below a deck) and not necessarily the tank itself. Gas fumes accumulating in an enclosed space is what you want to prevent, not necessarily just venting the tank.

Your tank is under a vaccum from your motor when it is running, hence the reason for loosening the cap or vent plug on a portable tank. If it doesn't have a vent, it can't pull gas into the carb(s) and will quit. The vent pulls dual duty and lets the expanding gasses escape when the motor isn't running.

It's a portable tank. I get the part about the vent incorporated into the filler cap but don't know if I should worry about the fumes collecting in the area enclosed by the deck. I don't want to make a problem where none exists, I'm just wondering if it's something anyone has had to deal with.

In MN we are required to carry a fire extinguisher if the tank is enclosed. It makes me wonder whether that's due to a potential for fumes to build up. A little boat like mine wouldn't have a bilge vent in any case so I was trying to find out if any other venting method was necessary or smart. Just trying to play it safe...

bobberboy said:

In MN we are required to carry a fire extinguisher if the tank is enclosed. It makes me wonder whether that's due to a potential for fumes to build up.

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That is absolutely the reason. In KY, it used to be if you had enclosed decks or a floor where fumes can be trapped. Now it is simply if there is a fuel tank onboard to clear up any grey areas in the law.

If I had a near air tight space enclosing a tank, I would vent that space and call it good.

OK. Thanks.

that vent is only to vent a built in tank so it doesn't "oil can" and allows air to escape when filling . you need compartment vents , one facing forward and one facing rearwards to vent the compartment. a blower with hoses attached to one also helps and a hose attached to the other one running to the lowest part of the compartment. this hose is made for blower systems and is approx. 4" similar to a dryer hose.

Natural Ventilation: A natural ventilation system is required on all boats with compartments that contain a permanently installed gasoline engine or a fuel tank, unless that space is open to the atmosphere.

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https://www.ehow.com/how_4725772_install-inline-boat-bilge-blower.html

this is the type of vent I am referring to .

https://cdn.cruisersforum.com/forums/attachment.php?s=30e25dbc769bbbb3b1af289a2f8f3096&attachmentid=11511&stc=1&d=1259962996

I've never been too much of a fan of venting a tank below decks, even with the fore and aft deck vents. I'd rather get the fumes out of there from the get go, then have the fore and aft vents just for additional airflow, incase fumes manage to escape somewhere.

What I've done, is run a vent line from the tank filler cap. Unscrew and remove the vent screw. You'll find that in most cases, the threads are 1/4" NPT. A 90 degree nylon fitting 1/4" NPT to 1/4" barb and some flex hose, vented to a safe location will fix your problem. I had a quick disconnect fitting about 6 inches from the cap, so the tank could still be removed from the boat for filling, and the cap easily removed.

My thoughts on it are real simple..Safety first. If you even think that you have a gasoline fume buildup, install a fan to suck 'em out of there. I narrowly escaped some very serious burns from exploding gasoline fumes a few years ago. You wouldnt believe the fireball that came from only a 1/4 gallon of gasoline.