Guidance on converting from portable gas tank to onboard tank w external filler

Just bought a small pontoon boat that has a 30 hp Mercury 4 stroke. It came with a portable 6 gal gas tank strapped to rear platform/deck. I want to change to a permanent tank that I’ll install in a rear covered compartment, with a filler hose running to an external gas cap (so I can fill from our dock). Looking at a Moeller tank, but not sure of all the components I’ll need. Obviously a filler tube/hose, external cap, low perm 5/16”:fuel line etc. But what about venting? Do I get a cap that has some sort of built in vent, or get a separate vent hose and vent thingy, or ? Also - current setup has a small device in the fuel line between tank and engine (see pic) - any idea what that is? Current portable tank has a cap with a vent screw that you open when using boat…

Many thanks!
-Mike

 

Permanent fuel tanks must be vented overboard.

Metallic filler lines must be grounded.

A combination plastic fill and vent line would be my advice for you.

Any enclosure should allow access to all fttings on the tank.

A tank sender and gauge is best way to see fuel levels.

 

Thanks FallGuy! I’ll look for a plastic fill w vent. Using marine rated low emis flexible fuel line (not metal). Any idea what that contraption in my photo is?

 

Attwood 8M0044687 Fuel Demand Valve https://www.boatandrvaccessories.com/products/attwood-8m0044687-fuel-demand-valve

 

Check your local regs as many installed tank requirements are much more stringent than for portables.
Also, check with the manufacturer's recommendations and caveats.
In other words: "Read the instructions", much better than putting your trust in forum members who have zero accountability or vested interest.
Buyer beware!
Cheers!

 

https://www.uscgboating.org/assets/1/AssetManager/ABYC.1002.01.pdf

All 135 pages of the fuel regs

 

Most fuel regs apply to inboard vessels. So fortunately, what OP has planned is not too hard.

Another thing to do is consider a drip loop on the vent line. This is so any water splash that enters the fuel vent cannot flow downward. Not sure if the regs require it, but it is a pro practice at least.

Modern perm tanks are required to be diurnal with a charcoal canister. However, this is for boats built post 2011. And the standard is a bit pathetic, if anyone wants my opinion. The reason I say pathetic is because standards that cannot be more broad sweeping for me are not ideal. An ideal standard would be possible for existing vessels to comply easily. So, for example, something in 5/8" vent line that anyone could add to reduce emissions would be good. Or, a system that allows an existing tank lower emissions. Or a new vent cap that eliminates zero pressure emission while allowing pressurized emission.

 

Yes most US fuel system regs apply only to inboards, but ABYC standards, ISO et all apply to both inboards and outboards. Plus that the EPA doesn't care what type of boat it is, if it has a fuel system and it was made after 2012 it has to comply with the emissions standards. But everything else Fallguy said is good advice. Besides if you buy new hose it will probably be EPA compliant anyway. And other new fuel system fittings will more than likely be compliant. Personally, I like a separate vent line but there are a lot of combo, fill and vent fittings available.