Quote:
| Originally Posted by [b Quote[/b] (Mark Chase @ Aug. 27 2003,15:38)]Both Dom and WL have posted profiles with over 100% cns post dive. 114% and 117%. Also they both use multiple stages for travel and deco I note that neither diver is a trimix diver.
Also Doms use of bottom gas is due to the GUE (DIR) philosophy of set gas mix so he has the choice of the folowing gas list:
Bottom Mix
3-30m
In real |
Whoops, half of my reply is missing so it doesn’t make a lot of sense.
It was supposed to read
Available DIR bottom Mix
3 –30m 32% Nitrox
33 – 45m 21 / 35 Trimix
48 – 60m 18 / 45 Trimix
63 - 75m 15 / 55 Trimix
78 – 121m 10 / 70 Trimix
Available DIR Deco Mix
6m 100% 02
21m 50% Nitrox
36m 35 /25 Trimix
58m 21 /35 Trimix
DIR divers are not suposed to use any other gas mix than these. This can and does result in high CNS profiles and missed deco for the He
As a result the dive plan is limited to and by the available gas mix. This results in extended deco unless (as WL suggested) you ignore the He in the mix. This is a new thing with DIR and it should be noted that ignoring the He in the deco mix reduces the deco on my profile by 10mins. So according to the dive soft where the DIR diver will have missed 10mins of stops. It is notable that DIR have not had the courage of their conviction to put this new theory into their planning soft where. The Americans are a litigatious bunch and I don’t think GI3’s arguments would stand up to scientific scrutiny at the moment .
The use of 100% for deco in 60m for 30min profiles is also going to push the CNS clock over 100% which is not advised by any other agency. Unfortunately DIR do not allow the use of 80% for deco so there is no option but to push the CNS over 100%
Whilst these arguments have been gone over before I think it is important to highlight them again for people reading these threads who might have a limited background knowledge. It also answers the question as to why Dom’s profile used such a strange choice of back gas.
Also 50 –90 is quite an aggressive profile and does not provide deep stops to alleviate Micro bubble formation. This level of dive is better dived on low GFs fro the deeper part of the deco to provide the deep stops or Pyle stops as they are popularly referred to.
So I personally would opt for a 20-80GF using the ZHL16B model
Back gas would be 18 / 40 trimix P02 1.35 at 65m
Travel 32% Nitrox
Deco 80% 02
Stops in time and depth
1 @ 42m ascend and switch to 32%Nitrox @ 40m
1 @ 30
1 @ 27
2 @ 24
2 @ 21
3 @ 18
5 @ 15
6 @ 12 Switch to 80% on ascent passing 10m
7 @ 9
34@ 6
Total run time 96mins
Total deco time 62mins
CNS post dive 52%
OUT 125.24
The point of noting that WL and Dom don’t do Trimix diving was that they would perhaps not have experience of the problems associated with multiple stage bottles. Anything past two bottles is to be avoided if possible. That said I do use a pony of air attached to my twin set as a bail out to first stop depth. This idea is also used by some of the other deep trimix divers in my circle but the mix is redundant and not part of the deco plan.
5min stops for gas switch is also a bit odd as gas switching takes all of 10seconds. Also an additional 5mins at the first switch depth will add to the on gassing of the Nitrogen in the mix which would have to be planned fro in the deco. Prep in the from of unsheathing the reg and hose checking it is the correct mix and switched on and purging the reg is done on ascent. So it’s just a case of reg out reg in. I usually do this on ascent and switch the mix on the computer on the stop.
I am not having a go at any one. I am just looking at some of the practical considerations when planning deco.
ATB
Mark Chase