Oxygen, how much at night

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jonjo

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The recent thread on getting entombed in cockpit lockers highlighted this is a concern shared by many yacht owners. Having 3 visitors aboard for the Trafalgar 200 event revived another long held fear of mine namely asphyxiation of the crew at night.

How much ventilation do 4 adults actually require in an otherwise water tight and airtight yacht hull?

As I walk around a marina in the evening I note some crews closing up for the night leaving a single hatch in a vent position and wonder if an ambulance crew will be extracting bodies the following morning.

At the end of the day the ventilation issue must be overblown in the minds of boat owners, otherwise in these safety conscious days every opening portal on a yacht would be plastered with dire warnings that it should only be shut in winds above force 7.
 
Jonjo.....chill out mate, if you worry about ventilation with guest on board what about farting? Maybe its time to take the sleeping bag up on deck if you feel this way! /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif
 
But Jonjo is right! Carbon dioxide is heavier than oxygen so in a still cabin with no through flow of fresh air your crew will end up asphyxiating in a bowl of CO2. That is why at night the hatches should be left open to allow new air to come in and the seacocks should be opened and the pipes taken off to allow the CO2 to drain out of the bottom of the boat.
 
Years ago I had a small yacht with a meths burning stove. Two of us were sleeping one night and it was freezing, so of course the hatch was well sealed and burned the stove for a while to get warm.
I woke up in the middle of the night breathing very heavily and with a cracking hangover.
I never did that again.
 
Well no matter what the weather I always sleep with the windows open, in my opinion anyone whom sleeps with everything shut is a 'soap dodger'!

So if they choose to die in thier own stench then good luck to em! /forums/images/graemlins/wink.gif
 
[ QUOTE ]
But Jonjo is right! Carbon dioxide is heavier than oxygen so in a still cabin with no through flow of fresh air your crew will end up asphyxiating in a bowl of CO2.

[/ QUOTE ] But it doesn't have be fresh air..
[ QUOTE ]
ventilation with guest on board what about farting?

[/ QUOTE ] this is natures own way of providing a change of air during the night. Perfect!
 
[ QUOTE ]
this is natures own way of providing a change of air during the night. Perfect!


[/ QUOTE ]

/forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif
 
There are usually 2 seacocks - one for letting in water and the other for letting out CO2, quite clearly marked - just open the CO2 one ...
 
All this chat about CO2.......What about methane gas!

Supposing there were eight people tucked up in their bunks after eating a good curry, of course each person had also consumed the lethal additive of around 6 pints of lager.

Would you advise keeping the bilge pump on all night?
 
Re: Start again

Ok let's try and get back to pure science!

In a theoretical air tight and water tight yacht how many cubic meters of atmosphere does a human require during 9 hours of rest to avoid:

1 - Mild carbon dioxide poisoning resulting in a headache?
2 - Serious carbon dioxide poisoning causing death?
 
Re: Start again

Facts you require are

15-18 breaths a minute
500 ml average volume excanged at rest
% co2 before breating in 0.03%
% co2 after breating in 3.6%

Therefore
A healthy man exhales CO2 at about 220 mL/min at rest and 1,650 mL/min during moderate exercise

Headaches with 2-3% CO2 and long exposure

at 6% noticable effects can be measured - (hearing loss!)

So estimate you cabin size and off you go!

I cant see how mine can be air tight and spiders and mossies can still get in.


Facts from http://books.nap.edu/books/0309054788/html/105.html
 
Re: Thankyou

Your figures explain why we are not dropping like flies at night in harbour but the safety margin is not that comfortable.

Over 9 hours an adult at rest will generate 108 cubic liters of CO2.
To avoid a groggy head in the morning we should keep the CO2 percentage below 2%.
So in an air tight yacht this equates to an initial 5.4 cubic meters of fresh air at the start of the night.
I guess there might be 30 cubic meters of free to circulate air in a 32 footer?

However I do feel justified in telling my sister last week-end that if she insisted on closing the quarter cabin door to eliminate the sound of snoring men she had to keep the mini cockpit porthole open even if it rained.

I always leave one washboard out whatever the weather so these calculations are a bit academic providing internal cabin doors are left ajar.
 
A Pleasure

Coor - you get 9 hours sleep on a boat - can I come sailing with you /forums/images/graemlins/smile.gif
 
Methane is CH4=16 so lighter than air and would tend to go up to the hatch. But we all know it doesn't and that's due to diffusion. Same applies to CO2, though heavier, it doesn't sink significantly because it diffuses. It takes really heavy stuff like butane (C4H10=58) to sink.

Geoff
 
Hello Geoff /forums/images/graemlins/wink.gif come to think of it, the heavy stuff (butane) has been a problem of mine in the past through eating large amounts of cabbage or brussel sprouts! /forums/images/graemlins/blush.gif
 
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