No matter what we add to the equipment mix for a particular dive,
nothing in the DIR scheme changes - everything stays the same because it
has been thought all the way out in advance. 

This perevents a last minute change or cluster in order to accomodate
some gear needed for a particualr dive. Very simple, in line with what
Sean is saying.


Sean T. Stevenson wrote:
> 
> On Tue, 21 Sep 1999 17:38:35 +0100, John Thornton wrote:
> 
> >Oh Absolutely!! I think that over here we have a problem with all the
> >gear on one side, as I said in my post we all agree that simple is best
> >but having all the deco on one side I have never understood. I did
> >assume that it was a development from the days that you had no deco gas
> >and the torch cannister was the problem, it is big for what you do so
> >the only place to put anything else ( at first only one tank?) was on
> >the other side, as things developed then all ended up on the other side.
> >Frankly I find that regardless of how well it is signposted having
> >gasses on opposite sides is easier and less inclined to cock up.
> >Remember, no scoots, no big batteries for torches, streamlined for our
> >specific interests.
> 
> In addition to clearance for the light canister and for discharge
> thrust from the scooter, there are other reasons for keeping all deco
> gas on the left side.  This position produces less drag as compared to
> bilateral mounting, because the bottles are all in each others
> slipstream.  Try this if you don't believe me - much easier to swim
> with unilateral mounting.  Attitude offset is not an issue if you use
> the correct (aluminum) cylinders for stages.  Another reason is
> consistency, since with all bottles on the left the regs all feed the
> same way, every time, in the same fashion as both the back gas
> regulators.  In an emergency, conditioned responses are possible due to
> this consistency.  With the stages mounted orifice up, the valve knob
> is to the left, and in the event of a reg failure, can be easily
> operated manually to deliver gas, with the left hand riding on the
> bottle.  To do this on the right side, you have to mount orifice down
> (inconsistent rigging) or have some sort of convoluted hand position,
> and have the regulator rigged either from the wrong side or with a hose
> that is too long - neither one an attractive option.
> 
> >Rodger Rodger, I have never had a prob with this, its the gasses off one
> >side that I struggle with, it has to be easier to have your marking
> >system with the high and low gasses on different sides, the confusion
> >has to be less.
> 
> The problem with mounting high and low PPO2 gases on either side (other
> than the mere disadvantages of bilateral mounting mentioned above) is
> that this allows the diver to associate one side with a particular mix,
> which can lead to breathing off of a bottle without proper positive
> identification of the gas being breathed.  This is a CORE point of DIR:
> that a gas be identified solely by the prominent MOD markings and not
> by position, content decals, colour, mouthpiece, poodle jackets,
> tactile aids or any other stupidity.  If you cannot positively identify
> a gas, you do not breathe it, period.
> 
> >G you mark them in feet, we mark them in metres, not our fault, it is
> >the measuring system we use. With 50% our depth is 22m, normally21m is
> >marked to avoid a 1.6 po2. Confusing when an air tank marked 21% could
> >be close. Our bottles are turned off as well, not sure what you mean by
> >parked, is this left on the line? I assume so, we dont do this, probably
> >because we dont dive in caves and have options to surface.
> 
> It doesn't matter if you use feet or meters as long as you are
> consistent.  When I dive with Americans, we decide which units will be
> used, and then ensure that ALL bottles are marked identically, and that
> everyone dives with tables and gauges in the appropriate units.
> Confusing an MOD with contents should never be a problem, if ALL
> bottles are marked with MOD only, and every member of the dive team
> should know and agree what a 3" high number on both sides, horizontally
> in the orientation of the tank in its normal riding position, means.
> Anything else is an invitation to disaster.  Parked means that the
> second stage is clipped off at the first stage, near the neck of the
> tank and not anywhere else where it could potentially be mistaken for a
> different gas.
> 
> >Simple hose, simple guage and thats optional, thats all. The point is
> >you have to run with it on, I accept that. But remember if you use
> >redundancy to its full then this has to apply to all stages of the dive,
> >do you have redundant deco gas? If not then how do you cope with the
> >same failure scenario that dictates the whole twin set back gas
> >scenario?. The schedules used should always have a back up,the option
> >here is do you take loads of 32%, 40% or whatever( I am in your camp
> >about the 50% here and staying on the he) to cover the failure? or do
> >you have redundant backup? the back mounted o2 is there as a bonus and
> >should be regarded as such, ie shorten the deco, if it fails the your
> >set up is still safe and the desired result of getting home is still
> >okay, it just takes longer
> 
> John, your buddies are your redundant deco gas.  Dive better than
> thirds on everything, and for long dives, reserve the backgas for
> emergencies, oxygen breaks, and wing inflation only.  Carrying the
> oxygen is not the issue.  Carrying in on your back, in a high
> entrapment potential location, where you cannot reach it to free it
> should you become entangled, where it adds unnecessary drag that could
> be avoided by mounting it another way, where the bottle identification
> can not be seen, where it can not be quickly and easily handed off to
> another diver, where a first stage failure can not be immediately dealt
> with and gas delivery done manually, and where the second stage is not
> clipped to the bottle neck and stowed in such a fashion as to make it
> absolutely impossible to accidentally breathe off of this regulator
> without first making a positive identification of the gas, is the
> issue.  I can see you have given this a great deal of thought.
> 
> >Simple I agree with, your system is very specific and we all can learn
> >from it, it is not the answer to all types of diving.
> 
> True, but for self contained applications other than 1 atmosphere
> suits, it works everywhere.  Let me know if George takes you up on your
> offer to come out there and set things straight - I might be interested
> in a trip to Scapa Flow.
> 
> -Sean
> 
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