Stupid question about petrol

[Rivers & creeks]

Is petrol vapour lighter or heavier than air?

I'm moving the petrol tanks on our HT. We carry quite a lot (12gal) and it's kept in two plastimo upright tanks. The best place to site them is in a cockpit locker. This is the issue. In a sealed (but not quite air tight) locker there will naturally be a build up of petrol vapour from the air inlet to the tanks and from when we change over the petrol line from one tank to another. Therefore after a while the atmosphere could become 90% vapour! I want to vent the locker to prevent a build up of vapour, should it be vented at the bottom (darned awkward) or is near the top OK? If it was LPG it would have to be at the bottom of the locker, is petrol any different?

Thanks,

Simon

 

[ajt]

Not sure about this one but last year a motorboat caught fire in Hythe Marina (very close to my boat). Apparently the owners had recently refuelled the outboard, it was a still night so the vapour hung around the boat untill one of the crew lit a ciggarette, resulting in a fire in which the boat was lost and the one next to it was also a right off. One of the firemen said if there was a breeze then this accident may not have happened. Vent at both maybe

 

[Barr Avel]

Petrol vapour is heavier than air.
In case you don't just want to take my word for it...

 

[Talbot]

vent at the bottom. Petrol vapour hangs around the ground

 

[Bodach na mara]

Vent both top and bottom. Petrol vapour is more dense than air and will exit from the bottom. The drain must be overboard. Air to replace the vapour and encourage evapouration of any spillage must be able to get in at the top. This can be from inboard but is better from outboard as well. Under no circumstances vent to the bilge.

Having said all that, I used to carry petrol for my Seagull outboard on my old six-metre. It was in large plastic canisters tied to suitable points in the cockpit. Two points are relevant here. I do not smoke and would not allow anyone sailing with me to do so, and in the 1960s petrol was less volatile. I would not do the same today. I am very reluctant to allow the stuff aboard Wight Dawn at all and carry only a 5 litre plastic container at most. Plastic containers are better than metal, all of which leak eventually.

 

[alldownwind]

For what it's worth, I keep the small can of petrol that I carry for our tender, in the yacht's anchor locker. At least it's right up the sharp end away from everyone most of the time, and any vapour will vent overboard through the locker drain.

 

[Andrew_Fanner]

I stow petrol for the tender in a NATO jerrycan in the hold and have kept in service the old vapour alarm that was fitted before I converted to diesel. I don't have gas on board.

 

[Rivers & creeks]

I see what you mean about top and bottom. This is such a large quantity of petrol beacuse the HT27 is (usually) driven by an outboard through a central well in the cockpit.

 

[sparkie]

Hi Simon,

I'm very glad you asked this question. I have been looking to relocate my o/b petrol tank, and was thinking of a custom made integrated one until advised otherwise by Pat Manley (of PBO expert fame). I am now looking into constructing an enclosed "shed" for the thing.

I had always assumed that petrol fumes were lighter than air, probably due to the fact that I can smell fumes through the tank breather, but this was clearly wrong.

Back to the drawing board! When is someone going to manufacture a lightweight o/b diesel??

Safe sailing

Sparkie

 

[Elza_Skip]

That's a great idea to keep the can in the Anchor locker! I never thought of that

 

[youngwrinkley]

There is no such thing as a stupid question!