gas locker exhausting to outside

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bobg

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I am building a gas locker within a stern deck locker to exhaust any remote chance of a gas leakage through the upper hull. My puzzle is that if the boat heels over, will water gush into the gas locker even though on a flat sea the skin fitting exhaust point is above the water line? Is there a one way only skin fitting I can get that would let leaking gas go out, but sea water not come in.
 
Any water that enters through the skin fitting should run out as the boat levels out. So long as the gas locker is watertight then this shouldn't be a problem. If it isn't watertight then it wont be gas tight either. Have you considered the option of mounting the gas cylinder on a suitable bracket on the the pushpit. This is a common solution on Catalina 25s as seen on the owners website www.catalina25-250.org
 
It is a problem in small boats and I am planning to modify my locker which drains into the cockpit at present so that it drains to a point in the transom fairly close to the centre line.

I think any valve you fit will probably defeat the object of the drain unless you can find something with a float in it.
 
Can you fit the skin fitting in the transom?
What about those valves you get with snorkel tubes that have a floating ball in a cage? [might not be legal though]

I have this problem on my boat but it doesn't matter as the water drains out when the boat comes upright.
 
There is no reason why I can't put a skin fitting in the transom of my boat. Something that works like the ping pong ball in a cage was what I had in mind. Except that it wont be an open cage. It'll look something like this:

5f9d9cc4.jpg



The trouble I have is that the bottom of the gas locker is very close to the water line, and it can't be raised The drain can't, therefore, be in the very bottom of the locker so water coming in won't completely drain out again.
 
I'd be careful of fitting anything to do with gas that wouldn't be approved by a marine surveyor when it comes to selling (or even safety while you own it). Explosions may be very rare but surveyors are understandably twitchy.

When I bought a boat a few years ago with a venting locker the surveyor recommended that the locker sides be made higher and that a seacock was fitted so that if the hose fitting came off then I wouldn't end up with a flooded boat in rough weather. I asked for, and got, the amount to do the work off my agreed price.

I'm going through the same now with my current boat and have asked the boatyard to check out the current coding standards.
 
It was just an idea of something that would do the trick. If it does not exist then you cant fit it.
 
I thought Gas locker drains had to be at the lowest point of the locker - otherwise leaking gas won't drain .....
 
Normally you only need a 1/4" hole to drain gas so "gushing water" isn't a problem and if you can make the drain come out in the transom there is not much chance of water getting into the locker in the first place.
As for putting a ping pong ball into the system you will have a problem i.e. whilst the ball will stop the ingress of water by blocking the top hole, when it's not working the ball will block the exit of any gas.
IMHO you shouldn't be overly sensitive to this problem - simply put a hole in the bottom of the locker to drain it and forget about ant ingress of water as it will be to small to worry about!

Peter.
 
[ QUOTE ]
Normally you only need a 1/4" hole to drain gas <snip
Peter.

[/ QUOTE ]

19mm is the regulation minimum. The hose must also be fuel grade (fireproof) I do not have the ISO number to hand. I used a piece of eber exhaust I had over which is 24mm.
 
[ QUOTE ]

The trouble I have is that the bottom of the gas locker is very close to the water line, and it can't be raised The drain can't, therefore, be in the very bottom of the locker so water coming in won't completely drain out again.

[/ QUOTE ]

We suggest a solution for inland boaters, which might work for you. It can be found on page 7/12 of the BSS Essential Guide 2nd Edition. The aim is to raise the bottom of the locker and displace any gas that might have escaped the system.

Regards
 
Thanks for pointing that out to me. Although it was an idea I had thought of myself. Good to know at least one of my ideas woould be acceptable! Reading through all the BSS requirements etc is something I still have to do. There is so much of it!

In my case the drain will close to the bottom of the locker once it is modified but until I look at in detail I'm not sure if it will be close enough. Because the locker is only a few mm larger than the diameter of the gas bottle there is not be much space to fill and as it is square that will be just the corners. I assume wood is considered to be an lpg resistant material in this context.

The present locker is 9mm ply. Would that be considered adequate. If not what thickness would be. Alternatively should I be sheathing it in fibre glass or encasing it in sheet metal.

Section 7.2.1/R says the locker must be gas tight up to the top of the cylinder valves and other HP components. That implies that my current non gas tight lid is adequate or have I missed something.
 
There is a fairly simple answer to this. Assuming that the gas locker is on the port side you can take a pipe from the bottom of it over to the extreme starb'd side and then loop back to a skin fitting in the port side. This will provide a trap to stop water entering on either tack. You can only get a build up of gas when on one tack or the other but you will anyway when the skin fitting is underwater or closed by a valve. When you change tack or come back to vertical any gas build up will disperse. /forums/images/graemlins/wink.gif
 
Boatman, if you look at my sketch you will see that the ball is not blocking the bottom drain. There are many ways of preventing this but what I envisaged was the outlet extending a little way insde the main body to support the ball but partly cut away, or with slots or holes in its sides (equivalent in total size to the minimum permitted drain diameter) so that escaping gas can freely drain away.

It was only intended as a sketch of an idea for a device that would prevent water entering via the drain. It is not a detailed engineering drawing. If anyone actually wanted to make something like this then there are many considerations. Materials to be used for the body and the ball, making it so that it can be dismantled for cleaning or ball replacement etc etc.
 
Ping Pong ball ...

Given slots or suitable vents in bottom pipe that ball sits on ... gas will exit ... BUT how long before the ball is slimy and growth on it to stick ?

My locker is above w/line by literally only a few inches maybe ... >>>>

STERN.jpg


Extreme left is the gas locker o/bd ... to left o f GCC is the Bilge pp o/bd ... below that the engine exhaust and below the a/foul line are the two cockpit drains ...

My gas o/bd has a on/off valve in the locker that is permamently open ... ( provision if necessary to close in event of real bad conditions etc.)

In fact I forget about the valve until I lift out ballon and see it again !!
 
What about putting an aft facing cowl over the skin fitting...there is no way that it will block the escape of gas but as the boat will be moving through the water when the fitting it submerged the movement through the water will cause a suction effect on the cowl stopping water comming in and if there is any gas in there, sucking it out. It would work like an open dinghy self bailer. It will also be a simple fail safe solution, with any kind of valve there is always the remote chance of blockage. Sods law says that it is when your ping pong ball has stuck closed is when the gas will leak!! Cheers Iain
 
Re: Ping Pong ball ...

Ok It was dumb idea.
Clearly there is no scope for any positive development of the idea. We will throw it in the bin along with those automatic antisiphon valves that you can get for the engine cooling system and we'll accept that unless we have a boat large enough for the gas locker drain outlet to be best part of a foot above the water line like Super Anne's (My boat's transom is not much higher than that!) the bottom of the gas bottle locker will periodically fill with water, or we will have to make do with one of those stinking Primus stoves.

We won't of course because the engine will already have filled with seawater and we won't be going anywhere.

However by the end of the day I will expect to see a sketch of an idea that will overcome all the problems.
 
Re: Ping Pong ball ... wasn\'t daft ...

Just saw a small flaw that if it got dirty / wet etc. it could lead to sticking ...

The Seawych is limited to have a full service gas locker ... but my boat has a raised lid etc. in the port aft cockpit bench to accomodate ... so you could do same ? >>

best_pal_onboard.jpg


Sorry that piccie is offset ... but you can see my mates foot resting on it ...........
 
Re: Ping Pong ball ...

I don't think it's a daft idea, especially as I have been thinking of such solutions myself! My locker drain is at the lowest point of an overhanging stern, which floods when the boat pitches. The water runs straight out again, of course, but salt water in the locker doesn't do any metal work any good.

I have thought of trying a rubber flap valve on the outside - just a small sheet fixed on its lower edge, angled out slightly. This wouldn't prevent gas escaping, but should prevent most of the wave coming inboard.
 
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