Ewan

> Er..maybe you've met another.

Yup, and another - John is right on this one!  Neutral is neutral but   
what we are taking about is the lift needed at the start of the dive vs.   
that required at the end of the dive after a significant proportion of   
the gas has been consumed. We should be neutral throughout the dive   
(except ascent and descent).

>I've managed to convince myself that I lose up to about 24lbs during a   
dive
>due to gas usage and start off adjusted accordingly. It seemed to work   
for
>some reason.

I am told that air weighs 1.15 Kg per 1000 litres (1 Kg = 1lb, can't   
remember litres to CuFt).  So a set of 12 litre 232 bar doubles has 6.7   
Kg (14.7 lb.) of air.  An 80 (about 11 litres from memory) would have 5.7   
lb. of gas.  Now, my 10 l Ali stages with regulator are 0.5 Kg (1 lb.)   
positive when empty so I add 1 lb. for any number of stages (in the worst   
case you can always float empties to the surface).

So, at the start of the dive with these doubles and 2 stages, I need 27   
lb. of lift in my wing to obtain neutral buoyancy assuming no suit   
compression.  This assumes one is correctly weighted for neutral buoyancy   
at the surface with almost no gas in the cylinders.  It also assumes no   
suit compression.  The reality is that you plan on carrying a reserve in   
every cylinder so in practice you will always need gas in your wing to   
maintain neutral buoyancy.

I dive a crushed neoprene DUI suit which has little compression at depth   
so I can't comment on the amount of buoyancy loss for a conventional   
neoprene suit.  My DUI suit and under suit requires 12.5 Kg (27.5 lb.)   
for me to be neutral in sea water (obtained from doubles, backplate,   
torch and lead) due to the amount of gas within the dry suit and under   
suit required to achieve comfort.

David Shimell
Project Manager, Sequent Computer Systems Ltd, Weybridge, UK
Email: shimell@se*.co*

 ----------
From:  owner-techdiver[SMTP:owner-techdiver@aquanaut.com]
Sent:  19 January 1998 03:49
To:  'Jammer Six'
Cc:  'Techdiver Mailing List'
Subject:  RE: 3 missing in WPB

        >>.... he is going to need
> >>something like 40 lbs of negative buoyancy to get himself and his   
suit
> >>neutral at the surface....... he's carrying about 28 lbs of gas,   
which
> the
> >>wings are lifting at the start of the dive.....
> >>We're talking almost 70 lbs of required lift, just to get neutral at   
the
> >>bottom.
>
>
        >Wrong.
        >No wonder they can sell bondage wings.
        >Who taught you this crap?
        >Neutral is neutral.
        >I met an experianced, tech-trained, tri-mix certified diver on a
boat
        >last November who believed the same bullshit.

Er..maybe you've met another.
I've managed to convince myself that I lose up to about 24lbs during a   
dive
due to gas usage and start off adjusted accordingly. It seemed to work   
for
some reason.
One reason I'd preferred membrane drysuits was due to the belief that I'd
have to compensate for a lack of buoyancy at depth.
This could save me money, as I'm planning to buy a new suit.

Best regards, Ewan


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