gas tank vent shut off valve?

[nobrainsd]

I'm still working on an aluminum fuel tank installation in my zodiac futura. The tank did not come with a mechanical vent on the gas cap. The tank has an internally threaded filler neck so I haven't been able to find a vented cap for it. I am going to install a separate vent using the 3/8" port provided. Obviously I am not going to be able to vent over the side with my inflatable tubes! But I'm not worried because the plastic tank vents into my boat and the space isn't enclosed. Most boats with permanent tanks vent over the side and don't have a vent shut off valve at all. When my inflatable is stored in my garage or is being transported it seems to me I should include a vent shut off valve so that there is no possibility of fumes accumulating in the boat itself, sort of a combination of portable and fixed installation elements. I would appreciate any other comments or suggestions regarding this unique application. I was never very happy seeing water splash off my plastic tank with the little screw vent on the cap, at least now I'll have an antisiphon vent installed to make the system more impervious to water intrusion.

 

[kandil]

Re: gas tank vent shut off valve?

Is this tank going to be permanent or it is going to be removable? if permanent you will have to ground the tank to a battery for fueling to avoid any static charges or you have to remove it and put the tank on the ground to fuel.

 

[gobigkahuna]

Re: gas tank vent shut off valve?

Hi nobrainsd,

Guidelines for the proper storage and ventilation of gasoline is well documented and is the single biggest danger (IMO) on a small boat. Gasoline liquid is not only highly flammable, but its vapors are -extremely explosive-. I've witnessed numerous boat fires and explosions (two in your neighborhood, at the Harbor Island fuel pier) and it is not something you want to have happen (I get shivers just thinking about it).

If I were you, I would consult an experienced boatwright or marine surveyor and find out how it should be done. You are fortunate in that there are many experienced people in your area, take a walk down Shelter Island Drive or check the Yellow Pages. Get the right info, the right materials and make sure it's done right.

Good luck and have fun!

 

[nobrainsd]

Re: gas tank vent shut off valve?

Well, I do have more than average experience having finished a Westsail from barehull. But it is nice to get some different opinions from people here on the forum in addition to the ones I'm getting from "professionals". I have received an amazing array of responses! The installation is not permanent and will be easily removable, but I have spoken to a CG rep before and they considered my strapped down plastic tank "permanent" because I couldn't immediately pick it up and move it (any real fire and I'm out of the boat anyways). Whether the aluminum tank is portable or not I will ground it due to the conductive nature of the tank construction. Unlike most tank installations mine gets used with various configurations of my vessel. I don't always carry a battery, I have a smaller outboard that is just a pull start that gets used occasionally. That is why I was considering the methods of grounding that would best apply to my different uses. Refueling may be the most likely source of a spark, but I will be using a a ground wire to my trim tab anode when there is no battery installed and I won't be fueling that set up on my trailer. As far as the gas tank vent goes, well, I've been riding around with a 12 gallon plastic tank that just has a mechanically vented cap. Since the gas fumes are not heavier than air they dissipate quickly and as long as the fumes are not in an enclosed area it isn't a big issue. I've seen approved installations that vent into splashwells and deck fills with integrated vents that don't directly discharge over the side. Yes, I have had a professional state that I needed to put my vent on my transom, great advice for a boat with higher clearance above the water but more likely to introduce water into my fuel system on my low riding inflatable. I was also told that I didn't need a vent shut off valve and clearly most hard hull boats don't have one installed. But my application is a little different than most and I am going to put one inline so I can close the vent. That will keep vapors from being vented in my garage and protect from any possible fuel spill through the vent when four wheeling in Mexico. Not a lot of boats getting that sort of ride! I appreciate the concern regarding grounding and venting my tank. At least I'm taking it more seriously than the guy who motored past me yesterday in his dinghy with a lit cigarette while sitting directly on his vented fuel tank!

 

[gobigkahuna]

Re: gas tank vent shut off valve?

Not trying to start an argument as you obviously are doing your homework and are asking all the right questions, but there are a few bits I'll comment on:

Since the gas fumes are not heavier than air they dissipate quickly and as long as the fumes are not in an enclosed area it isn't a big issue.

First, gasoline fumes are heavier than air which explains why blowers are often required when a gas system is operated in an enclosed space.

Second, what about the area beneath your floorboards? That void between the floorboards and the V-bottom? Perhaps it's not a likely place for vapors to accumulate, but it is possible.

I've seen approved installations that vent into splashwells and deck fills with integrated vents that don't directly discharge over the side.

How long ago were they "approved" and by whom? I've also seen vents on sailboats that drained into a cockpit that might have passed an inspection many years ago, but failed during a recent inspection. The guiding documentation, BTW, is published by the ABYC ( http://www.abycinc.org/ ). I don't have a copy with me, but it would definitely be a good source of info for a project like this.

Yes, I have had a professional state that I needed to put my vent on my transom, great advice for a boat with higher clearance above the water but more likely to introduce water into my fuel system on my low riding inflatable.

Yes, sounds like a bit of a dilemma. I don't know what decision making process you went through before deciding on an aluminum tank in a soft bottom boat, but I think I would do more homework if I were in your shoes. Keep in mind, that it doesn't take much of a "spark" to ignite gasoline vapor. It can be caused by something as innocuous as accumulated static electricity from liquids sloshing around in the tank.

At least I'm taking it more seriously than the guy who motored past me yesterday in his dinghy with a lit cigarette while sitting directly on his vented fuel tank!

Oh, the sea stories I could tell!

 

[nobrainsd]

Re: gas tank vent shut off valve?

Yep, Gasoline vapors are heavier than air (with a vapor density of 3-4). But they are pretty easy to disperse.

Why the potential for fumes to accumulate in spaces like the one below my floorboard would pose a problem with a smaller aluminum tank as opposed to the big plastic tank I cannot imagine. The aluminum tank was supposed to come with a gas cap that incorporated a sight gauge and a mechanical vent. That is an approved use for an above deck tank that is not enclosed. The manufacturer has been having difficulty getting these caps for the internally threaded fill neck so they supplied a non vented cap and a vent port with a plug. Adding a vent tube and a shut off valve are equivalent to a mechanically vented cap, but would be superior in my application due to decreased probability of getting water ingress at the cap vent screw on the tank. This is why I'm not all stressed about the vapor being vented in the open boat. But it's also the reason I totally agree with you and choose to install the shut off valve. Anyplace I don't have adequate air movement, anytime I need to work on the electrical system or during transport I will shut off the vent. I appreciate your feedback. I do have respect for gasoline and it never hurts to minimize ones risk. I did consider mounting my vent valve on the transom, but it is not a dry location! Right or wrong I'm more comfortable with the in boat vent risk, just like the risk with my current tank, than I am with having fuel problems and ending up stuck! Thanks again for the discussion.