Gas in bilge

drew silverwitch

drew silverwitch

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I accidentally release a small quantity of calor into my bilges, and the gas alarm went off. I was quite pleased that such a small amount triggered it.
However I do not have a bilge blower, will the gas degrade and disperse over time and if so how long. If it doesn't how do you get rid of it without a blower
 
It will disperse over time but of course this is assisted by any ventilation you can provide. Open a few hatches and create a breeze. Be careful with blowers as many are not safe in gas as they create a spark.
 
We always used to purge any possible gas in the bilge by using the hand bilge pump as the gas is heavier than air and will be expelled, we did this fairly regularly as a precaution.
 
TWINSCREW said:
We always used to purge any possible gas in the bilge by using the hand bilge pump as the gas is heavier than air and will be expelled, we did this fairly regularly as a precaution.
Click to expand...

I wonder if this works. It would be interesting to do some kind of experiment. Pumping water and pumping gas are two very different things. I suppose it depends on the bilge pump.
 
TWINSCREW said:
We always used to purge any possible gas in the bilge by using the hand bilge pump as the gas is heavier than air and will be expelled, we did this fairly regularly as a precaution.
Click to expand...

Bilge pumps are generally pretty useless for pumping gas.
The valves often don't work well when dry, you can see this when you try getting one to prime.
And they only shift small quantities.
It's far more effective to open hatches and either retreat to the café or waft a board around to disperse the gas.
I think the OYC did a lot to popularise the bilge pump thing, I'm sure it was all about giving the oiks something physical to do?
 
TWINSCREW said:
We always used to purge any possible gas in the bilge by using the hand bilge pump as the gas is heavier than air and will be expelled, we did this fairly regularly as a precaution.
Click to expand...

pmagowan said:
I wonder if this works. It would be interesting to do some kind of experiment. Pumping water and pumping gas are two very different things. I suppose it depends on the bilge pump.
Click to expand...

Almost certainly a waste of effort, other than as physical exercise, for two reasons.

Firstly it is unlikely to pump air efficiently

Secondly you'd need to shift several times the volume of the space to thoroughly ventilate it. If the space was say 1/2 cu metre and the pump, even if pumping air efficiently, could shift 50 litres per minute at a realistic pumping rate you would need to be pumping for "several time" 10 minutes. 40 or 50 minutes perhaps , preferably longer.
 
VicS said:
Almost certainly a waste of effort, other than as physical exercise, for two reasons.

Firstly it is unlikely to pump air efficiently

Secondly you'd need to shift several times the volume of the space to thoroughly ventilate it. If the space was say 1/2 cu metre and the pump, even if pumping air efficiently, could shift 50 litres per minute at a realistic pumping rate you would need to be pumping for "several time" 10 minutes. 40 or 50 minutes perhaps , preferably longer.
Click to expand...

Yes, I have to say that was my first thought. I suppose one of the problems with gas in the bilge is should you really abandon the boat until it is cleared. I have heard that gas can explode at quite low concentrations and perhaps wafting the bilge could move some of the gas to an ignition source such as electrics. I wonder if such potential sources of ignition could be isolated. For instance, if the gas alarm goes off it wouldn't be too hard to have the electrics switch off at the same time. Overkill perhaps. I suspect for the OP opening a few hatches and spending an hour in the pub will suffice.
 
pmagowan said:
Yes, I have to say that was my first thought. I suppose one of the problems with gas in the bilge is should you really abandon the boat until it is cleared. I have heard that gas can explode at quite low concentrations and perhaps wafting the bilge could move some of the gas to an ignition source such as electrics. I wonder if such potential sources of ignition could be isolated. For instance, if the gas alarm goes off it wouldn't be too hard to have the electrics switch off at the same time. Overkill perhaps. I suspect for the OP opening a few hatches and spending an hour in the pub will suffice.
Click to expand...
It's normally advised not to switch things off, as that is more likely to cause a spark.
The lower flammability limits of propane and butane are between 1 and 2%, well above the level most people can smell the additive.

Bear in mind a cubic metre of air is about 1.2kg, so a camping gaz bottle can make a big volume explosive....
But a bit of hissing from the cooker won't be much mass of gas.

Always err on the side of caution though!
 
lw395 said:
It's normally advised not to switch things off, as that is more likely to cause a spark.
The lower flammability limits of propane and butane are between 1 and 2%, well above the level most people can smell the additive.

Bear in mind a cubic metre of air is about 1.2kg, so a camping gaz bottle can make a big volume explosive....
But a bit of hissing from the cooker won't be much mass of gas.

Always err on the side of caution though!
Click to expand...

Yes, I understand that switches can cause sparks but I was thinking that the switch to isolate power could easily be somewhere wheer it would not come into contact with any gas leak, i.e. not in the bilge. The gas alarm should detect the leak early and isolate the power to reduce the risk of ignition. As I said, it is likely overkill and if you have an alarm then it is probably easy enough to immediately turn off the gas and ventilate. Some gas regulators can be powered so that they would shut down automatically.
 
lw395 said:
Most are brushless these days FWIW.
You might cause a spark connecting it up though!
OTOH nipping down to Maplins to get one is an alternative displacement activity to going to the pub....
Click to expand...

It is certainly not a preferable displacement activity though! It is sometimes hard to find a really good excuse to spend an hour or two in the pub and I don't think this one should be wasted! :)
 
It is quite interesting because you don't often think about what you would do if you have a known leak. You might have an alarm to let you know but then what do you do. Perhaps the safest thing is to isolate the gas, open the hatch and get off but I know human nature is to try to fully alleviate the problem. What you don't want is an alarm that lures you into the bilge where you get blown up!
 
lw395 said:
Bilge pumps are generally pretty useless for pumping gas.
The valves often don't work well when dry, you can see this when you try getting one to prime.
And they only shift small quantities.
It's far more effective to open hatches and either retreat to the café or waft a board around to disperse the gas.
I think the OYC did a lot to popularise the bilge pump thing, I'm sure it was all about giving the oiks something physical to do?
Click to expand...

Surely a centrifugal one would do the trick? They are a bit like fans anyway (and there are no valves).
 
This thread reminds me of an incident to a friend some years ago. We were at Dartmouth and my friend's wife accidentally turned on a burner on the gas cooker with her hip (before the advent of safety valves) as she was passing. It was several minutes before my friend realised what had happened and turned off the gas. It must have seemed strange to the neighbours as he was seen apparently bailing "nothing" out of the boat with a bucket. He was of course bailing butane out of the bilge. Needless to say I stayed well away until the task was complete (being the coward that I am).
 
theoldsalt said:
This thread reminds me of an incident to a friend some years ago. We were at Dartmouth and my friend's wife accidentally turned on a burner on the gas cooker with her hip (before the advent of safety valves) as she was passing. It was several minutes before my friend realised what had happened and turned off the gas. It must have seemed strange to the neighbours as he was seen apparently bailing "nothing" out of the boat with a bucket. He was of course bailing butane out of the bilge. Needless to say I stayed well away until the task was complete (being the coward that I am).
Click to expand...

That is another example that would immediately make me wonder about the effectiveness of such an operation. I suspect that the butane would not be sufficiently dense to fill the bucket in that way and instead it would simply be stirred up potentially raising the internal concentration high enough to cause an explosion. It would be a bit like trying to bail cold water out from beneath a layer of hot water. You end up with all the water lukewarm.

The imagery is great though :)
 
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