Gas vent

[philh]

A recent survey on my little Seawych bilge keeler has indicated that the starboard cockpit locker, wher I store a gas bottle needs a vent. Anyone any ideas wher I site the vent and how do I stocp water ingressing etc.

As you can see quite new to the whole keel boat thing having moved on from dinghies

 

[sailorman]

20m/m Dia pipe req ( so im told by surveyor) from lowest point within the gas locker & vented O/B.
mine goes out the transom & as its well above the w/l its not normally in the water, only a large following sea would reach the outlet.
the locker is totally sealed so no water ingress to worry about

 

[penultimate]

The stowage of gas is problematical and my own would not satisfy the latest requirements. This is because my locker vents into the cockpit and the cockpit drains are underwater. Because I can reach the cylinder valve and shut it off at the bottle, as well as shutting off at the galley, I still believe this ia a better arrangement than some much bigger boats with gas bottles only accessible from the bathing platform for example. I'm not familiar with the layout of a Seawych but believe your cockpit locker extends to the transom? If so, can you build a gas-tight locker in the top of the cockpit locker with a drain through the transom close to the waterline? This would be easier to construct if you have sufficient side deck space to make the gas locker top opening, but I doubt this is the case.

 

[VicS]

Welcome to the forum

I have sent you a pm about the gas installation on my Seawych

Vic

 

[silverseal]

I dont believe in gas lockers - in N America they have RV, caravans and leisure boats which have a Federal requirement, that the gas bottle is kept outside the vehicle or boat. Hence you see them on the back of boats, and on the rear of RVs etc.
I do the same, but pretty the thing up by placing it in a very expensive stainless container designed to fit onto the pushpit - or the alternative is to go into any DIY superstore, (the Range in Gosport is good) and look for stainless steel pedal bins, which are designed to be just the right size to accomodate a gas cylinder. Get a couple of stainless mounting brackets and you are in business.. all you then need is an off /on tap (outside the boat), a rubber gland to take the 8 mm pipe which is led into the boat and connected to the appliance via nice new bit of flexible orange hose.. total cost about £25.

Any leaks from the regulator valve, and bottle vents itself naturally to atmosphere, and does not drain into the bilges - ( how do you bale a bilge full of heavier than air gas anyway?)

 

[Vara]

Bailing gas

[ QUOTE ]
how do you bale a bilge full of heavier than air gas anyway?

[/ QUOTE ] When I did my first Offshore sailing course the instructor said that when taking over the boat you should pump the bilge and when water stopped being ejected you should carry on for a further 40 strokes of the pump to clear any gas that had collected.I never worked out whether he was extracting the ***** or not but have done it ever since.

 

[VicS]

Re: Bailing gas

If gas sank to the bottom of the bilge and stayed there like a liquid there might be some merit in that but in reality, although it might sink at first, it will slowly diffuse throughout the whole volume of the space. Take a look at your children's science books and you'll find experiments to demonstrate that fact.

 

[Vara]

Re: Bailing gas

Oh yes Graham's Law---silly me /forums/images/graemlins/mad.gif

 

[john_morris_uk]

Re: Bailing gas

"Pumping an extra 40 pumps for the gas" is one of my pet hates.

I suggest it doesn't work and it wears the pump out for when you might need it for its proper purpose!

Ventilate the boat properly, and fit a gas alarm. Make sure your gas locker vent isn't blocked and use a bit of common sense with the dangerous stuff.

If you are really paranoid you don't have to have gas on board, but most of us sail safely with the stuff around without blowing ourselves up!

 

[dickh]

I added a gas locker on a Vivacity 20 some years ago. I made up a plywood box, only accessed from the top, cut a round hole in the deck over the locker, bolted the box to the underside of the deck with mastic. Fitted a round Bomar hatch in the deck(I believe they are cheaper Italian copies now) and the a drain pipe out the transom. I fitted a bulkhead fitting in the side for the copper pipe to the cooker. I used a Calor Gas 4.5kg cylinder, but the Camping Gaz is just as good but a smaller cylinder and more expensive gas(except in France).

 

[silverseal]

Re: Bailing gas

Ok how having looked at my Physical Chemistry degree course tome, it does not tell me when the diffusion process has completed..
The object of the exercise is prevention rather than cure - if the gas bottle is on the back of the boat in free air, then the problem does not arise does it??

 

[VicS]

Re: Bailing gas

I'm not going to consult the text books on this but I think the time taken for the diffusion process to be absolutely and toally complete must be infinite.

Hell I've looked it up any way. Grahams law states that the rate of diffusion of a gas is inversely propotional to square root of its density. (for density you can read molecular weight or, in modern money, relative molecular mass, RMM.

So that means, yes it goes on for infinite time but the important thing is that the lower the density the faster it happens in the initial period. Hydrogen with a RMM of 2 diffuses very quickly. Butane with a RMM of 58, 5.4 times slower and bromine vapour with a RMM of 160 nearly 9 times slower. (I hate that "times less" expresion that you hear so frequently nowadays.)

Both hydrogen and bromine vapour are used in schools to demonstrate gaseous diffusion. Hydrogen only takes a few minutes to effectively diffuse completely(downwards) between two gas jars while bromine vaopur diffuses (upwards) during the course of a lesson.

And it's going to take the rest of the evening for 40 years of dust from "Glasstone and Lewis" to settle

 

[Guest]

Has to be low in the locker as gas is heavier than air .... so if bottom of locker is lower than waterline - you'll have to fill in the locker till above w/line and raise the bottle - which of course will now upset the hieght of the locker ??

My locker si set into the aft port 1/4 of the cockpit with a 1/2" drain overboard at base of locker .... it also has a small valve on it just in case its necessary to close off due weather etc. BUT the valve is not operable with hand - it needs a flat spade end key (large screwdriver is enough) to stop people inadvertently turning it off ....

 

[macd]

The trouble with using a port or starboard (rather than stern) locker for gas is that the regs require it to drain steadily downhill at all angles of heel, which usually requires more plumbing and can be tricky (or even impossible) to arrange. Some of us are probably less fussy, but it's bound to be picked up next time your insurer asks for a survey.