Gas alarm sensor placement

[JumbleDuck]

I am pretty sure that the non-waterproof gas sensor for my Dual Watch LPG/CO alarm got flooded, so I have taken the whole thing out and will shortly fit a replacement. I'd love a Nereus, but can't afford it, so probably a Pilot. I have been thinking about the sensor siting. Low down, obviously, but the previous sensor was in the bilge, but that's below a pretty well sealed cabin floor. Would I be better to put the sensor just above the floor?

 

[LadyInBed]

Would two in parallel, one above and one below the sole work?
I can't think that they wouldn't.

 

[J Neeves]

If the cabin floor is 'well sealed' and you locate the alarm there then there seems a chance you could be asphyxiated before the alarms goes off. I'd locate it just above the floor - which presumably is more like the environment you will occupy.

 

[Dougal]

I'd be inclined to rethink about the 'Pilot' gas alarm. I've had to replace sensors (at silly money) three times in six years!!! The manufacturer says it can only be SALT contamination. I STRONGLY disagree but they wont bend on the matter! Sure there's a little bit of 'sour grapes' from me, but i'm 100% certain that two out of the three were nowhere near any salt water. Any water come to that!

 

[JumbleDuck]

If the cabin floor is 'well sealed' and you locate the alarm there then there seems a chance you could be asphyxiated before the alarms goes off. I'd locate it just above the floor - which presumably is more like the environment you will occupy.

Thanks. My feeling is that while a very slow leak might permeate to the bilge before it diffuses, anything big enough to more about will probably be above the cabin floor. The alternative might be to replace the brass lifty-and-pull ring on the hatch above the bilge (and above the current sensor position) with a thumb hole, giving the gas an easy way to drain down. Even then there is a lot of bilge below the current sensor level. Hmm.

I'd be inclined to rethink about the 'Pilot' gas alarm. I've had to replace sensors (at silly money) three times in six years!!! The manufacturer says it can only be SALT contamination. I STRONGLY disagree but they wont bend on the matter! Sure there's a little bit of 'sour grapes' from me, but i'm 100% certain that two out of the three were nowhere near any salt water. Any water come to that!

Thanks. The Nereus does look very much better, with waterproof sensors, but at three times the price. Ouch. One alternative might be the Amos LPG alarm, which did well in Sailing Today's test. However, it's not listed on the Amos website and Socal are selling them off at £90 reduced to £50, so I wonder if they have been discontinued.

 

[Tintin]

Look for Trio gas CO alarm on fleabay.

V good and affordable and you can have up to 3 sensors.

 

[pvb]

If you're that worried, why not simply turn the gas off at the bottle when you're not using it?

 

[JumbleDuck]

If you're that worried, why not simply turn the gas off at the bottle when you're not using it?

I do. Flame failure devices on the cooker, too, so it's belt, braces and whatever comes after belt and braces. Velcro?

 

[pvb]

I do. Flame failure devices on the cooker, too, so it's belt, braces and whatever comes after belt and braces. Velcro?

So what on earth are you worried about?

 

[JumbleDuck]

So what on earth are you worried about?

If I'm going to have a gas alarm it might as well be in the best place.

 

[J Neeves]

Is the best place directly under the item that is most likely to cause any issues, like the stove?

 

[Kelpie]

One sensor under the cooker, another under the cabin sole, twin channel Pilot alarm. Sensors do fail due to damp, dust, etc.

 

[JumbleDuck]

One sensor under the cooker, another under the cabin sole, twin channel Pilot alarm. Sensors do fail due to damp, dust, etc.

Thinking about it a bit more, if the pipe from the bottle to the cooker fails, the escaaping gas will go into the cockpit locker and from there drain via the engine compartment to the billge. That's probably a worse situation than a leak at the cooker, which I would smell, so I'm coming round to the view that one sensor at least needs to be in the bilge.

How I wish I hadn't sold my lovely Optimus 156 twin-burner and oven quicklighting paraffin stove a few months before buying this boat!

 

[J Neeves]

Looking at your costs then upgrading the pipework would be cheaper than the alarm (unless pipework in the UK is unreasonably expensive). New pipe ought to have a decent life and the likely points of leak would then be restricted to joints (at the bottle), stove and any valves in-between. You might also be able to re-route without the need to pass through the engine compartment. If your bilges are well sealed then keeping the gas out seems sensible (especially as this appears to be the worst location you have for a sensor- damp etc, it also seems the worst place for gas to accumulate as if the sensor fails you will not smell it (its well sealed).

I'm assuming the gas bottle is located 'outside' or in a locker draining 'outside' the boat. Why will any leak drain from a cockpit locker to the engine bay? Can this locker not be 'better' sealed, or holes (to the engine bay) be high and drain, from low down, into the cockpit.

Jonathan

 

[JumbleDuck]

I'm assuming the gas bottle is located 'outside' or in a locker draining 'outside' the boat. Why will any leak drain from a cockpit locker to the engine bay? Can this locker not be 'better' sealed, or holes (to the engine bay) be high and drain, from low down, into the cockpit.

The gas locker is an inset which sits under the lid of my lazarette locker - a bit of a pain because, the boat being a double ender with a quarter berth, I only have one deep locker and a rope tray (above the berth) in the cockpit, and the lazarette would be very useful. Hence my long term plan (see Wanted forum) of an Origo 6000 ethanol stove instead.

From the gas locker the pipe runs under the coaming in the cockpit locker, which is onlt separated bya sheet of ply with various holes from the engine compartment, though which it drains to the bilge. Seeling that off would be a heck of a job and would still need a connection to the bilge. I've no reason to doubt the gas pipe, by the way, it's just that if it did ever go I could fill the bilge and the engine space with gas without knowing. Press the starter button ... kaboom.

 

[J Neeves]

Having read your posts in the past I knew you would have thought most of this through and have discounted the obvious - I was idly posing questions! Then another option is to better ventilate the engine bay and bilges with an engine blower (or sucker).

Is it considered un-seamnlike to take the gas cylinder out and place it in a dedicated transom bottle cage (outside)?

Suggesting religiously turning the gas off is not an option - religions are not infallible.

I have this feeling the only option is the one you arrived at yourself - locate one sensor in the bilge.

If its any comfort, though boats blowing up make great headlines they do not do it that often (in fact so seldom that when they do they do make headlines), and usually the finger is pointed to petrol not gas.

Jonathan

 

[JumbleDuck]

Suggesting religiously turning the gas off is not an option - religions are not infallible.

I have this feeling the only option is the one you arrived at yourself - locate one sensor in the bilge.

If I had the money (hah!) I'd get the Nereus setup with two LPG sensors (bilge and cabin sole) one CO sensor (cabin roof) plus a remote solenoid at the gas bottle. Unfortunately that systum (WG300-LLC-V) costs £456 ...