Q for PADI Instructors re: Master Scuba Diver

In article <hqPEd.4305$C52.2375@newsread2.news.atl.earthlink. net>,
Lee Bell <leebell@ix.remove.netcom.com> wrote:
>>>The key to getting it right is to *totally empty* your BCD before going
>>>down. It was only when I went to the Similan Islands a couple of years
>>>ago that the avuncular 'Charlie'Lidureau of Seafarer-divers.com pointed
>>>this out. But he was right. I spent a fortnight in a shortie swimming up
>>>and down using just the air in my lungs to tweak my bouyancy. The only
>>>time I put air in my BCD was at the surface or once to combat a strong
>>>down draught.
>>
>> Then you have a very good shortie. I always have to adjust bouyancy at
>> 12-15 and again at 27-32 to have a comfortable breathing pattern. This is
>> with 3mm fullsuit, separate surface buoyancy around 3 kgs.
>
>There are several issues being addressed in this thread. I'm going to leave
>the drysuit issues for drysuit divers except to say that having to carry gas
>in a suit for thermal protection changes things considerably.

Yep. I think some of the "guru's" from southern waters really don't
appreciate how significant this is. I think the debate of "BCD or suit"
inflation would evaporate if this is the case.

>Buoyancy control with nothing more than changes in breathing patterns is
>only possible with minimal free gas. That generally means little or no gas
>in the BCD and as little as possible in a wetsuit. My only thermal
>protection is a rear entry 3mm wetsuit. No, I'm not complaining or
>bragging. That's just how it is when you live in S. Florida.

In Britain/Norway a shell suit with something like 400g thinsulate plus
a layer or two of wool is used in winter. It is important to leave the air
in the garments to make them stay good isolators. I can go up to 16 kgs
of lead on long, cold winter dives. We are talking of +/- 2 degrees C here.
(Record dive : -2 degrees water, -32 air, January 27th 1997)

In the summer season (10-16 degrees) 200g thinsulate is usually
enough, and 8 kgs of lead works fine with that. As a reference; I use
1-2 kgs if I dive without a suit; and 4-5 in a 3mm. This 3mm is said
to be of "compressed neoprene" and doesn't get the negative "kick"
before around 7-8 meters. To keep a normal breathing pattern I need to
adjust the BCD at 12 meters with this suit. (Yes, I have tried to
measure this). I then need to re-adjust at 4-5 on the way up.

With 200g thinsulate you need to adjust bouyancy every two meters or so.
Going down to a wreck on a line with one, continous inflation for the first
25 meters is not unusual.

>Now I'm bragging.

Possibly, but it is enlightening to have all the detail.

>I begin my no wetsuit dives with no gas in my BCD. Depending on the tanks
>I'm using, I'm very, very slightly negative (not noticable and easily
>controlled by breathing patterns) to slightly negative negative (noticable,
>could be controlled by breathing patterns, but why bother). Generally, when
>I reach a depth I plan to occupy for a while, I give the BCD a short shot of
>gas to get as close as possible to dead neutral. Before long, I vent that
>shot and continue and even end my dive with no gas in my BCD. This
>certainly contributes to my low gas consumption, but probably not nearly as
>much as being relaxed and comfortable in the water does. It's worth
>mentioning that "adjusting breathing patterns" does not mean pausing in my
>breathing cycle, at either end of the cycle. What it means is that I adjust
>the rate of inflation or deflation of my lungs. What is important is the
>average buoyancy. To rise, you increased the amount of time the lungs are
>full or near full. You breath in a little faster at the beginning of the
>inhale than at the end and breathe out a little faster at the end of the
>exhale than at the beginning. To descent, you increase the amount of time
>they are empty (as empty as they get) or near empty. The pattern is the
>reverse of the above. The change is quite subtle, so subtle, that it's
>unlikely someone watching would notice the difference, except for the fact
>that I move up and down in the water column.

Works like a charm with a wetsuit.

But when you have a residual volume of 15 liters of air in your suit you have
to adjust suit bouancy all the time. It is also important to do this so you
don't get cold. You have a heat budget you need to stretch with all available
means. Having the right amount of air in the suit is important.

This means we dump all air from the BCD at the surface, and do a frog kick
down the first 4 meters to avoid deflating and re-inflating the suit with
cold air.

As long as we carry less than around 6 kgs of extra equipment we just remove
some lead (rememeber it IS possible to stay down with less lead, we just get
cold very fast) and do all the bouancy with the suit. I find that this limit
is at around 6 kgs worth of equipment. This is enought for two stages and a large
light. Only when I attach a large video camera is there a need for the BCD to
come into action.

I guess this is what some agencies call "inflate suit until comfortable, then use
BCD". It is just that the "then use bcd" never arrives on a non-technical
winter dive here for a correctly weighed diver.

The BCD is important as a bailout device though. As a rule of thumb it
needs 1 1/2 times as much lift as the weights you carry (counting
lights etc as weights) A flooded suit will become _extremely_
negative. Tested this in a pool; a 18 kg BCD was unable to give
pusitive boyancy to diver with fully flooded shellsuit, 2x10 rig,
light and 12 kgs of lead.

>When wearing my 3mm wetsuit, things are only a little different. I suppose
>it varies, but my wetsuit does not compress much in the first 5 meters of
>the water column. At about 5 meters, there is a sharp compression and
>noticable change in my buoyancy, one that I normally adjust for by adding a
>small bit of gas to my BCD. Once below 15 feet, the wetsuit still
>compresses with depth, but in a more lateral fashion, only changing my
>buoyancy slightly as I change my depth. Generally speaking, I'm pretty much
>where I am when diving without my wetsuit (except I'm carrying a couple kg
>more weight). I'm adjusting for some pretty significant changes in depth
>only by a slight change in my breathing patterns. Because of the sharp
>change in buoyancy at around 5 meters, you may assume that I try to avoid
>planning a dive that includes that depth more than twice, once on descent
>and once on ascent. I know that sounds like a real newbie to UK divers, but
>it's more significant than it looks at first glance. A lot of very nice S.
>Florida diving is quite shallow. I still do the dives, I just do them in
>the summer, when I can leave my wetsuit in the closet.

The cold water here is usually worst in the 0-6 meter range; so we try
to minimise time there. Winter diving is seldom deco dives, and we stay
reasonably shallow and go for 34-36% nitrox so we can take a stop right below
the cold water, and just have a slow 2-3 minute ascent through the cold water.

>At any rate, the poster that said he could adjust quite well in a 3mm
>shorty, with little or no gas in the BCD is consistent with what I
>experience on almost all of my dives. Those that can not achieve very
>similar results, with similar thermal protection, have an opportunity to
>improve their warm water diving skills and, in doing so, increase the sense
>of freedom and comfort that such diving brings . . . that any improve their
>air consumption.

As I said, it is a very normal thing for northern, experienced divers to
have this problem in warm water. The flip side to the "drysuit course"
is sometimes sorely needed.

>
>> Perhaps we should really do the "wetsuit diver" submission to PADI.
>
>I've said before and this is a good chance to say it again. Those that
>believe they are "better" divers because they dive drysuits, often have
>missed the fact that, just as they develop skills almost to the automatic
>level that I would have to work to match, us warm water divers develop
>skills the drysuit divers would have to work equally hard to match. For
>each group, what we do most often, is what we do most easily.

I notiece this on the air consumption. I have two "bands" of air consumption,
around 11.5 liters/min SAC for the really good, "zen" dives, and around 14-15
for everything else. Nothing in between. If I change environment there are
at least 2 "high sac" dives before I settle in, likewise going the orher way.

I also noticed on a warm water dive there was sudden strong current, strong silting,
and general stress; then the drysuit reflexes came back instantly. Yes, it
is what you are used to.

-- mrr