[diveinfo] From a while back, about drysuits...

[Jean-Sebastien Morisset]

Subject:    Re: Drysuit diving
From:	Chris Elmore
Date:	Wed Mar 06 13:47:20 2002
    
There seems to be a good bit of interest in this so I'll answer the
people who emailed me on the list instead of privately.  The problem
with using the drysuit for bouyancy control is that you can get major
shifts in the center of lift as the gas moves around within the suit.
This means that once you move off of a stable (horizontal) position the
dynamics tend to move you further away from that position instead of
correcting back to it. With the wings as the primary control the center
of lift is isolated to within a few inches of the center of gravity.
Here's how it works in practice: At the surface you want to purge
("burp") the suit using a wrist or neck seal. If you are using argon
inflation you probably want to do this a couple of times to ensure that
most of the gas in the suit is argon. Make sure the arm vent is in the
full open position before the dive. Adjust the wings to acheive neutral
or slightly negative bouyancy. During the descent you add only enough
gas to the suit to avoid the squeeze from being shrink-wrapped. This
keeps suit bouyancy to a minimum and also keeps you streamlined for
scootering or swimming. Any additional bouyancy control is handled with
the wing inflator. This is why the DIR setup allows simultaneous
operation of the drysuit inflator, wings inflator/dump, and mask (for
clearing ears). When you start your ascent, the arm vent will dump any
excess gas automatically leaving you to deal with just the wings- the
same way you've been doing BDS (Before Dry Suit). In the normal precess
of going up and down you may end up with some gas in the suit that
doesn't want to leave through the arm vent. In this case it may be
necesary to get slightly head-high to facilitate the purge but, with
practice, this shouldn't be necessary (a la "flexing the python") Things
(can) change slightly at deco. You don't want the suit to be tight to
the point of constricting blood flow anytime during deco. Also, since
you're moving around less you may want more gas in the suit as
additional insulation against the cold. So, close the arm valve and add
gas to the suit while dumping gas from the wings to maintain the desired
bouyancy. I usually wait until the longer stops to do this. Remember,
deco is not naptime- you need to be keeping an eye on your buddy(s) and
timing breaks.
C.
Chris Elmore
(803) 348-3055 mobile
----- Original Message -----
From: "Chris Elmore" <elmorec@attglobal.net>
To: "Jean-Sebastien Morisset" <jsmoriss@mvlan.net>; "Quest Mailing List"
<quest@gue.com>
Sent: Wednesday, March 06, 2002 10:59 AM
Subject: Drysuit diving
> JS,
>      I don't know why the agencies and even the drysuit manufacturers (it's
> in the manual) insist on teaching the drysuit as the primary bouyancy
> control. When I got mine I read the manual and went to the lake- it was a
> one man CF. I was laughing so hard at the ridiculousness of it that my buddy
> offered me his long hose reg. After that, Jess Armantrout taught me how to
> dive a drysuit via email. It was simple and it works.
> Whoever teaches the GUE Fundamentals of DIR course can cover this in about
> five minutes. You won't get a "merit badge" to wear around like you would
> with PADI but you'll know how to dive a drysuit. If you need the basics
> before you take the FoDIR course contact me offline. The best advice I got
> from Trout was, "Make sure the suspenders are right *before* you put you
> legs in the suit".
> C.
>
> Chris Elmore
> (803) 748-3055 mobile
-- 
Jean-Sebastien Morisset, Sr. UNIX Administrator <jsmoriss@mvlan.net>
Personal Home Page <http://jsmoriss.mvlan.net/>
Underwater and Travel Photographs <http://www.mvpix.com/>