Ted

>Some say to use the
>drysuit for buoyancy, leaving the BC deflated, except on the surface, while
>others are saying nearly the opposite.

You get conflicting advice from the agencies too.

The simple answer is to put gas in your suit for comfort and then gas in your
wing for buoyancy.  "Comfort" can mean to avoid squeeze and for warmth in
colder conditions.

On the assumption that you are correctly weighted, the gas you put in your
wing is to offset the weight of the gas you are carrying.  So, at the end of
your dive, you should have little gas in your wing.  The gas will weigh very
roughly around 2Kg or 4-5lb per cylinder.  Now, if you dive a single
cylinder, it does not really take very much extra gas added to a suit for the
suit also to be used for buoyancy.  Agencies like this because it is simple
and allows control of one device for buoyancy and there is some sense in
this. However, read on.

The problem manifests itself when you go to doubles and stages.  Say you are
carrying doubles and 2 stages - this is roughly 4 times the weight of gas and
so requires a considerable amount of gas in the suit for buoyancy.  What
happens now is that the suit is no longer comfortable and gas migrates all
over the place.  Maintaining your attitude in water and general control
becomes more difficult than had you used your wing in the first place.  A
second, though lesser consideration is that gas in a DIR wing will provide
greater lateral stability due to the position of the wing wrapped around the
cylinder vs. gas in the suit.  The wing holds the gas at the extremities of
the wing which is wrapped around the doubles and this is further out than the
line of the body.  This leverage, allows easy compensation for asymmetrical
weighting due to equipment and generally better stability altogether.

So, now is the time to decide.  You can use you suit when diving singles; but
your wing when diving doubles and stages.  Alternatively you can elect to
develop a consistent practice and routine and use your wing for all buoyancy
control in all configurations.  The answer must be the latter.

On a philosophical point, there are configurations that are not DIR but
"work" (sub optimally) in some environments.  It is not until the diver is
exposed to different environments and conditions that the reason for a
seemingly small equipment configuration change or practice becomes obvious.

I hope this makes sense.

David Shimell
shimell@se*.co* <mailto:shimell@se*.co*> 
DDI: 01932 814096 * Mobile: 07770 282 202 * Fax: 01932 814343
Project Manager, IBM UK Web Server Division, Sequent Computer Systems
Limited,
Weybridge Business Park, Addlestone Road, Weybridge, Surrey, KT15 2UF, UK
registered in England and Wales under company number: 1999363, registered
office as above

-----Original Message-----
From:	Ted Phelps [SMTP:tphelps@ph*.co*]
Sent:	Wednesday, March 15, 2000 6:05 PM
To:	Peter Fjelsten; Jim Cobb
Cc:	techdiver@aquanaut.com
Subject:	RE: How to shoot a lift bag / trim problem

I'd really appreciate some feedback here, because I get conflicting opinions
both here and amongst the divers with whom I hang out.  Some say to use the
drysuit for buoyancy, leaving the BC deflated, except on the surface, while
others are saying nearly the opposite.  I've done two drysuit dives, having
done all of my other dives in Hawaii.  I'm back home in California, and my
drysuit is on order.  Can anyone give me some guidance?

Ted

-----Original Message-----
From: Peter Fjelsten [mailto:fjelsten@ma*.do*.dk*]
Sent: Wednesday, March 15, 2000 3:54 AM
To: Jim Cobb
Cc: techdiver@aquanaut.com
Subject: Re: How to shoot a lift bag / trim problem

Den 14-03-00 11:45 -0500 skrev Jim Cobb (At 14-03-00 11:45 -0500 Jim Cobb
wrote)...
>Sounds to me that you have too much air in your drysuit. You need to keep
as
>little air in your DS as possible and use your wings to control your
>buoyancy. Then you are "hanging" from your doubles and and your rig won't
>slip.

I continually read this on TD.

OK you warm water people - when you dive really cold water you wear more
undergarments than in 20 C water. Therefore the suit holds more gas than in
warm water. Also, you want to keep a fair amount of gas in the suit to stay
warm. Therefore "as little as possible" to prevent squeeze definitely is
less
than to keep warm.

Please keep this in mind.

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