Fuel Tank Vents

[ca va]

I am renovating a 22 foot motor boat that will be powered by two 115 or 150 hp outboards. It has two aluminium fuel tanks with approx 250 litre capacity each (one per engine) situated under GRP cockpit seating mouldings. Do these tanks need to have overboard air vents or can they be vented internally in the tank space.

[CDK]

Overboard air vents, no doubt about it; well protected against water entering by siphons or a self closing valve in the through-hull.

And they should have a generous diameter, otherwise filling is an agony.

[ca va]

Thanks for that

[baeckmo]

Originally Posted by CDK

Overboard air vents, no doubt about it; well protected against water entering by siphons or a self closing valve in the through-hull.

And they should have a generous diameter, otherwise filling is an agony.

Perfect comment; just add that the overboard vent openings should be installed at a higher level than the filling openings.

[gonzo]

The best position is the outboard well sides.

[tom28571]

That is where I put mine Gonzo. A paper towel laid in the well below the vent can catch any fuel spurt although this has not happened yet.

I don't know how one fits the vent higher than the fuel fill unless the fill is inside the boat and I would not like that. Best place for the fill vent is on the deck and there is nothing above that.

[baeckmo]

Having the vent opening higher than the filling neck allows filling from pumps with automatic cut-off in the handle, without spitting fuel from vents. There is always a way to arrange the proper installation, if you understand why to do it.

[tunnels]

Originally Posted by ca va

I am renovating a 22 foot motor boat that will be powered by two 115 or 150 hp outboards. It has two aluminium fuel tanks with approx 250 litre capacity each (one per engine) situated under GRP cockpit seating mouldings. Do these tanks need to have overboard air vents or can they be vented internally in the tank space.

Petrol fumes are exsplosive so would you want those fumes hanging about inside your boat ?????
any where in you boat for that matter !!!.
Glass boat burn !! usually to the water line, then sink rather quickly !!
The vents need to be external where possible and vents needs to be 300mm higher than the tank filler if possible . Any of this make sense ??

[gamage]

"Greetings from Sri Lanka”

Dear all,

Kindly send me contact details of air vent (fuel tank) suppliers???
(GL approved, 50mm )

Thank you

[michael pierzga]

Many yachts use a two vent system on the fuel tanks ...one jumbo vent only for high pressure refueling and one small vent when the engine is use or standing still. . The jumbo vent has an on off valve, is vented overboard and this valve is always closed during navigation to prevent water ingress. The small vent is permanently open, also exterior , disceet , high up and well protected from salt spray, typically with a inverted "J" form.

[Ike]

I just want to add that every accepted standard (ABYC, ISO, MCA, Det Norske veritas, US Coast Guard and so) requires that fuel tanks be vented to the atmosphere. Also that the vent must have either a flame arresting screen on the vent fitting or the vent line itself must act as a flame arrestor on it's own. The vent line needs to be designed so water won't get in. Usually this is achieved with a loop at the top of the line ( the line goes up, higher than the vent, and then back down to the vent.) And I agree, if it is possible the vent should be higher than the fill.

[ca va]

Thank you all for your good advice. I shall fit vents as you suggest.

[Landlubber]

...don't forget to insert fine wire gauze (flame arrestors).....

[milutin]

sorry to bother you, i do not understand this and can someone be so kind and explain to me how 22 footer with twin 115 even 150 hp plus two aluminum fuel tanks with approx 250 liter capacity each,(that is 7 meters boat with 500 l petrol on board) plus occupants, how that can float on the first place, let alone to pull skier or something

thanks

[Ike]

What do you need, an explanation of load capacity?