Ventilation of Gas bottle container
Can anybody advise if any further ventilation is required on the Swan aluminium gas locker in which the gas bottle sits?

I have the bottom drain in the locker which then leads to the through hull pipe, is this sufficient? I have seen that some gas system installers are saying you need more.

John B
Swan 411 010

Dear John
Pls see the thread dated April 10 2013
Kind regards
Lars

Dear Lars, thanks I have just read the thread. 2 winters ago I renewed my pipework at the bottom of the tank. The old pipe frequently got water up it and was partly blocked with weed etc. I had a large gas escape whilst sailing along the South Coast to Cornwall earlier that year. Fortunately I had fitted a gas alarm. I called up the Coast Guard to advise them of my situation, switched off everything electrical and sailed on to the nearest port which was Brixham. I was prevented from entering the port as I was considered a danger to shipping. After ventilating and pumping, all was well. Having replaced the damaged joint behind the cooker I was told that my system also needed to be updated so that the pressure can equalize in the aluminium tank. So later I checked out and replaced the discharge to sea. But from what I see this is not enough and I now need to allow further escape of lighter gas but not into the bilge. Given our set up this is near impossible.

Dear John
Thank you for the information.
To be considered a danger to shipping is a very serious matter.
Could you pls post some photos of you present installation, the Forum may be able to propose improvements.
Kind regards
Lars

Lars, my installation is the same as other 411s. The regulator is attached to the gas bottle and by a rubber hose to the through cylinder fitting. The only modification I made was on the underside of the cylinder lid a stuck a rubber gasket to try to seal off the cylinder. This I tighten down and form a hopefully air / gas tight seal. So if I had a gas escape then the gas could only exit by the bottom discharge and not seep out through the top of the cylinder and into the bilges. But now I am not sure if this is a correct course of action.

John
An escape upwards for the gas could be arranged as follows:
Make a connection through the lid for a vent hose and lead it out through the aft coaming.
It would be possible to improve further on this - eventual leaks from the cylinder can not any more drain into the bilge if a tight stowage locker with space for the cylinder at one end is built, fitting the port helmsman's seat circumference accurately so it can be made gastight around the edges.
Kind regards
Lars

John,
your report made me shudder with fear and I am very glad you had a gas alarm. I wonder if you have also a remotely activated shutoff valve like I have found in my boat because that would positively prevent a large escape of gas for any failure while the cooker is not in use. A clearly visible lamp near the cooker shows if the valve is activated so all crew is strongly encouraged to leave it on only for the strictly necessary time.
If you do not have the valve, I advise to fit one especially after your experience: it is small, placed inside the gas bottle container and very easy to fit.
Daniel, 411/004

John,

Ours is what I consider a conventional set-up; Gas cylinder in an aft locker, with overboard discharge at the bottom of the locker; naturally vented at the top. (I'm not sure making a gas tight seal at the top is required/sensible, as any gas leak, needs to have a supply of air to replace it!) The regulator is connected via a flexible to the internal pipework, which makes it way the galley; and a armoured flexible connects that to the cooker. We have a gas alarm sighted under the cooker.

We have ours inspected/tested every year. (Gas Safe, what use to be Corgi)and the makeup as described above has never been an issue. We have over the past 7 years had to replace elements of it due to failures/minor leaks. (Which given the number of people that never have a test is a bit worrying).

I would contact your local marine (and you need a marine guy) Gas Safe tester and have him inspect your system. If you are Cowes based, I can drop you a name etc.
Cheers
Adrian
Tiderace II

I agree with Daniel - a solenoid switch to the regulator activated from the galley with a clear on/off light is a must. As long as the switch is used it will prevent any leakage in the pipework between the cylinder and oven. I have 2 sensors on the alarm - one under the oven and one low down in the lazarette. First boat rule - "switch off the gas when the kettle has boiled!"

Rob

Sarabande. 47/029

Dear Adrian
Please note that one cubic foot of propane liquid will boil off into approximately 270 cubic feet of vapor. A significant leak in the gas compartment will cause it to overflow, and if there is an open path into the lazarette the gas will end up there, and drain to the bilge.

A remotely controlled gas shut off valve enables an additional way of restriction.
If the burners are extinguished by closing the remote valve this leaves no pressure in the feed line, and further reduces the amount of gas that can escape.
Kind regards
Lars

Guys. Thanks.
I was thinking of fitting a new gas alarm this winter and to have 2 sensors, one in the bilge sump which is close to the cooker and the other in the lazerette makes sense. I have been looking at a system which also monitors carbon monoxide as well as gas. Not sure where the best place for that CM sensor would be. I have never been keen on the solenoid on/off but will give this some serious thought.
It is clear that creating a sealed cylinder is not the solution to deal with an escape from the cylinder, so I will need to follow Lars suggestion and lead a pipe overboard.
The incident on the South Coast was the most frightening I have had in many years. I told the coast guard that I would radio in every 30 minutes, if I did not then they should come and pick up the pieces. It was quiet a challenge trying to clear the yacht of gas and stop the alarm buzzing. I hove too outside the harbour, opened all hatches and started pumping like crazy with the hand bilge pump.

Lars,

Agree with you; sorry I have seemed to misinterpret the physical setup/arrangement.

Our gas locker is sealed from the interior of the yacht. It is in a self-contained locker. The locker obviously has the overboard drain, and is naturally vented at the top. Any gas leak at the cylinder will either drain through the overboard drain, and/or spill overboard an/or into the aft cockpit.

I would not recommend, under any circumstance, that a gas cylinder is able to vent into the interior of a yacht. That would be a fundamental design flaw and completely unsafe. You certainly would not get a gas certificate in the UK if that was the case.

Cheers
Adrian

Ouch!
This is indeed quite a subject!
For the last 30 years I just have changed the rubber pipes close to the cooker and to the bottle when they were out of date (printed on it), and thought that keeping the gas cicuit as simple as possible was the best solution to avoid leaks...
Procedure up to now is only yo close the valve close to the cooker when not used, and leave the bottle open for, dare I say, most of the summer!!!
Now I start to be worried...
Original installation same as on the 411...
No gas detector installed in the bilge... I will definetely put one!
Any opinion in the forum about bubble gas detectors to be installed near the bottle?
Kind regards.
Philippe 41/022

Dear Philippe
The bubble leak detector is a simple and reliable device, no electronics or electrical power. It shows if there is a leak in the system when everything is closed.
Kind regards
Lars

Exactly, same use of the small manometer. It is a useless device for judging the remaining gas because the pressure of LPG does not fall until all liquid is evaporated inside the gas bottle and it is obviously too late; although not everybody knows it, its only use is for finding leaks. Close the gas bottle and check how long it takes for the pressure inside the circuit to fall. A fast fall - I would add also any not-extremely-slow fall - is a sign of trouble which requires further prompt investigation.
Daniel, 411/004

Philippe, we seemed to have had the same approach. The simpler the system, the fewer joints the likely fewer problems. Also easier to fix.

One of a number of reason why I have never fitted an electric bilge pump. GAS release into the bilge and BOOM.

Hi everybody,

I can only recommend the system mentioned by Daniel and Rob. In particular, it makes the shut-off of the gas bottle so easy that crew does it regularly. My impression is that the more "effort" a measure takes, the less often it will be taken (see the discussion about preventing accidental gybes) so I am quite familiar with boats that have the gas bottles open all summer or at least all day, with just a shut-off over night.
The remote switch we have installed costs slightly more than a hundred euros, but on the plus side it is easily connected to the regulating valve that connects to the bottle and can then be almost forgotten. Opening the gas bottle is simply throwing a switch in the pantry. Shutting of the bottle after cooking is the same. The system is connected to the gas sensor, so that when the gas alarm goes off the remote switch automatically shuts off the bottle.
We have a second manual shut-off close to the stove (which is also operated before and after cooking) so we can check the gas system for obvious leaks and do so regularly. I am aware that the electric system is not failure-proof, as nothing is, but we never experienced a problem. If the switch fails, the effect is immediately obvious.

Hoping for no leaks at all, gas or not,
Martin (Age of Swan, 48/039)

John,
please notice that the remote shutoff valves on gas lines we are talking about are well proven devices used for years in the caravan industry and many other vehicle applications. No need to add that they are extremely reliable and, although electrically operated, they will not trigger themselves an explosion.
I am probably wrong but I thought that their installation was indeed required by some Marine Register.
Daniel, 411/004