Thomas,

The dual aluminum 80 thing refers to diving in the open ocean with a
wetsuit in  south Florida.  The general idea is to simplify the gear
wherever possible to minimize the charlie foxtrot when it happens. 
Obviously this is not going to be the case if you are diving in cold
water with a drysuit.  

When diving a drysuit in the ocean we would use steel tanks (104s). We
would not use a second buoyancy compensator for the reasons George has
reiterated.  The drysuit is your emergency buoyancy device and when you
are using it for that purpose don’t complain about the neck seal
ballooning.  This leads me to ask you what type of drysuit are you
using. The very uncomfortable neck seal balloon problem is especially
typical of neoprene drysuits which are a whole different and sensitive
topic of discussion.  

Our early experience with extra bcs was that they invite a cluster.  Add
to this situation deep air, which seems to be the norm in most of the
diving we are hearing about. Now you have two low pressure (lp) inflator
hoses which have to be routed and serviced.  LP inflators are one of the
most common failure points, not only on the hose but on the inflator
valve assembly of the bc.  Shraeder valves are notoriously unreliable
and sometimes they fail in the "on" state.  In this situation a leaky
push button valve can result in unintentional inflation. Add to this the
fact that you are using the whole mess in seawater (most of the time)
which further diminishes the effective life of the valve.  Even in fresh
water these valves are a constant nuisance due to electrolytic and
suspended particulate matter effects.  One other interesting problem
with dual bcs involves one bc (such as if you are using bondage wings)
displacing the other bc and preventing it from inflating or worse
causing the overpressure dump valve to open on the second bc (especially
on the dual bladder jobs - a real bright idea).  Layering all sorts of
claptrap onto yourself does not make your diving safer. In our opinion
this is analogous to pouring urine over yourself and running into the
enemy machine guns. On the contrary, rather than make things more safe
you are in fact creating more pitfalls and static hazards.

You echo the standard "what if" scenario that many people love to bring
up when justifying elaborate and convoluted measures. I.E. what if
something happens which causes me to have to use all of my gas and stay
down much longer than I expected thereby precipitating a whole cascade
chain of life threatening events. My first question to you would be
"what would you be doing in the first place to extend your exposure well
beyond a safe bottom time?"  You are in fact choosing to do something
which knowingly violates your basic dive plan if you are really thinking
ahead as to the consequences of your actions.  Mix deep air into this
equation and you are really asking for trouble when it comes to the
rationale judgment department.  I would also ask you where is your life
support dive team member when you do get yourself into this "unexpected"
situation? Oh you’re not diving with a buddy on an extreme exposure gas
dive ?  There are some people who do this sort of thing solo, but I do
not want to discuss this because I believe you are not referring to this
practice. 

We have learned in extended range extreme exposure mixed gas cave diving
(and these policies and procedures are cast firmly into the WKPPs
operating methods) that thinking ahead through most possible
contingencies before the dive and then diving on "red alert" as an
integral team member avoids the sorts of problems that lead to what we
call the "stroke" way of thinking.  Gear configuration is a large part
of this "doing it right" methodology and the possible impact of  gear
convolutions when the charlie foxtrot occurs.  

Notice I say "When" and not "if".

Regards,


Bill Mee

Thomas A. Easop wrote:
> 
> Bill Mee wrote:
> 
> > That is one of the primary reasons we dive double 80s in the ocean
> > because they are as you say  "like corks" when they are empty.  In the
> > first place neither I nor George have ever breathed them down to the
> > point where emptiness is even a remote issue. In the event we had to
> > breath them down to that point it would be because the dive boat had
> > left us adrift and those two floating cylinders would give some
> > additional comfort while waiting for the Coast Guard helicopter. You can
> > easily swim aluminum 80s to the surface without a buoyancy compensator
> > if you are using Scubapro jetfins. This eliminates the need for the
> > additional bc or other buoyancy device required when you are diving with
> > cement blocks on your back. Nobody likes to walk back to shore along the
> > bottom.  Furthermore, in the last several years I have never breathed my
> > gas below 2000 psi while diving dual 80s in the ocean.
> 
> > What we have here is the usual conundrum of one problem begetting a
> > recursive series of complications. This is so typical of the situation
> > in socalled technical diving. If you dive with very negatively buoyant
> > tanks you now need to layer on all sorts of additional safety measures.
> > This is akin to driving with a gas can on the front seat of your car
> > because the capacity of your main fuel supply in inadequate.  Now to be
> > safe you must carry a fire extinguisher and wear an asbestos suit.
> Most steel tanks are only negative when they have gas in them. Most are about
nuetral (+/- 1-2 #) when low or
> empty (operationally). I can swim mine up without my BCD assistance. In your
example with Al cylanders, if you
> do encounter a problem and use most of your contents, then you can't maintain
depth during deco and there is
> nothing you can do about it. And your deco obligation may naturaully be more,
if your situation is an extended
> bottom time and unexpected use of gas available, like if you got lost or
stuck.
> 
> This sounds to me like the conundrum you allude to above.
> 
> If my wieght belt has enough lead on it or I have additional non essential
equipment, e.g. video light
> batteries, with me that are negative enough to counter my suit bouyancy at
the end of my dive when my tanks
> are operationally empty, I will only be negative at the beginning of the
dive, when the tanks are full. That
> is the best time to prevent a problem and also deal with one, such as losing
positive bouyancy capability. And
> the easiest solution to that is a redundant bladder in the BCD. The next is
to ditch some of the negative non
> essential equipment. In any event, the wieght of the gas in anyone's tanks
should not be the wieght that keps
> them form assending. Its usually less than 20 lbs, and everyone should be
cardiovascularly fit to overcome
> that with leg and fin power.
> 
> > We DO NOT perform long extreme exposure dives in the ocean. PERIOD.
> > I will not, and I know that
> > George will not, perform a decompression dive offshore that requires
> > anything more than two 40cf bottles of deco gas.
> 
> Good for you. Some others want to go deeper places, in the ocean, and there
is nothing wrong with that. If you
> only want to day hike so you will not venture too far from the road without a
heavy pack, etc., OK. Others
> want to and will.
> 
> Tom
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