In message <02F2632559134005*/c=US/admd=ATTMAIL/prmd=GOV+NOAA/o=CCNMFS/s
=Martinez/g=Anthony/@MHS>, Anthony Martinez <Anthony.Martinez@no*.go*>
writes
>
>Chris,
>
>Neither Pete nor I specified closed-circuit, but that is the type I was 
>referring to in my comments. I assumed that is what Pete was posting about 
>but you know what they say about assumptions... Pete which type of system 
>were you referring to?

Pete?

>
>Even when talking about semi-closed systems, they involve added equipment, 
>preparation and expense which you would not have with OC gear.

Added equipment? - apart from the rig itself, a bail out setup (which
you should have for OC) and a means to analyse the gas (which you would
have for OC nitrox/mix).

> In addition, 
>there are more failure points than with OC but those seem easier to deal 
>with, especially in light of the fact that you are probably carrying large 
>volumes of gas. 

Not sure I agree with 'more'.  The failure points are different, and the
system is SOOOooooo  simple.
 
>Then you have to ask yourself is the semi-closed system 
>increasing your efficiency enough to offset the increased operating 
>expenses and maintenance.

Gas is cheaper, due to smaller cylinders. Sorb is not that expensive,
and cost is spread per scubber over a number of hours of dive time.
Maintenance is the wildcard, since most goobers dive on unservicable (in
terms of functionality) kit anyway and have little concept of
preventative maintenance.
 
> If we are talking about helium/trimix dives then 
>maybe you save enough on He to buy CO2 absorbent.

Heliox/trimix? Not on semi-closed! - not yet (yea, - I know somebody has
probably done it etc.etc)

>
>I don't know Chris, you explain it to me. What exactly are you gaining with 
>semi-closed? Unless we are talking about long duration dives or remote 
>areas of the planet, 

3 - 4 days diving from one needing one small container of CO2 absorbent,
a 120cu/ft of nitrox to decant from and not much else.

>I just don't see any great advantages. - Tony

Neither did I until I spent some time using one.


Regards

Chris

E-mail:- chris@de*.de*.co*.uk*

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