Some initial MGR parameters on
@stuartv Oriskany Plan:
- Eanx70 gas switch depth at 40fsw (45fsw @ 1.6ATA)
- 5 to 6min ascent time including 1 min to problem solve and donate reg for emergency gas share at 170', and then ascend 30 fpm from 170fsw to 45fsw
- Emergency stressed SAC rate given above as 1.5 cf/min
- Average depth 108fsw on ascent from 170' to 45'
So Minimum Gas Reserve (MGR) volume of backgas is:
1.5 cf/min x (108/33 + 1)ATA x 6min = 38 cf
Therefore MGR for two Divers: 38 cf x 2 = 76 cf (round to 80 cubic feet for an actual Rock Bottom SPG reading of 1100psi). So 80 cf to get to Eanx70 switch depth of 45' from 170' in an emergency gas sharing contingency.
Total initial fill at 3500psi in double hp120's is 240 cf.
Hence Usable Gas Amount for Keep It Simple Scuba dive profile mission on Oriskany is:
240cf minus 80cf = 160 cubic feet usable.
No penetration, and keeping AL80 of Eanx70 clipped-on: use Rule of Halves -with 80 cf consumed outbound towards bow at 170' alongside Hangar Deck, and 80 cf back to tower mooring/ anchorline at the top of the Island/Flight/Bridge Superstructure. Delta Turn Pressure is 1100psi consumed and down from 3300psi for an actual Turn Pressure SPG reading of 2200psi. Option of using all 160 cf, traversing all the way at 170' to the bow and ascend up at bow's location mooring/ anchorline if Sac Rate & currents are in your favor -but you better be sure to close within the distance of the bow, and can see & reach the mooring/anchorline at the bow with 1100psi actual reading on the SPG, or else you've got a blue water ascent to deco under a deployed SMB.
If all is nominal & benign with no current and easy & low Sac Rate range of 0.6 to 0.7, you should have some time and gas to explore the Island/Bridge Superstructure at 140' to 80'. For a normal no current, no physical exertion ascent to your Eanx70 deco stop at 40fsw, expect to use only 25% of your MGR volume (20 cf); that will leave you with 60 cf of backgas to use after you complete your deco profile should any big pelagics or marine mammals come cruising by shallow to play with you.
Do you have a Nautilus Lifeline VHF broadcast beacon and/or a direct to SAR satellite PLB? And for exploring something this big, how come you aren't utilizing a scooter ? (For the WWII USS Saratoga Aircraft Carrier in Bikini Atoll 2013, we all brought DPV/Scooters to cover the grand tour over 888 feet of it's entire length, and depth ranges from 50' to 190' deep for eight consecutive days). . .
Also,
your 20/24 Trimix has a gas density of 5.57 g/L at 170fsw:
per Dr. Simon Mitchell's recommendations, a value of less than 6 g/L with plenty of margin is best for preventing CO2 retention, especially if you're expecting a high physical activity heavy breathing Sac Rate at 170fsw approaching 1 cf/min (again, you and your buddy should be using scooters for this reason as well, especially if working against a current at depth!). For future reference when you get full Trimix certified, a standard mix of 21/35 Trimix has a gas density of 4.94 g/L, and 18/45 of 4.33 g/L respectively at 170'.
What made you decide only on one big AL80 of Eanx70 with switch at 40fsw, instead of an AL40 of Eanx50 and switch at 70fsw? The MGR backgas volume going from 170' to 70' is 60.3 cf (round it to 65 cubic feet for a SPG actual reading of 930psi), instead of 80 cf from 170' to 45'. Also you start your decompression & off-gassing sooner . . .at 70fsw with Eanx50, and together with an AL40 Oxygen deco stop at 20fsw, you get a cleaner more efficient inert gas elimination from those stubborn supersaturated slow tissues, as well as two deco gases backing each other up if you lose one or have an unusable deco bottle scenario. . .
What's your deco schedule & profile look like for 170' with 23min BT and Eanx70 deco gas?
For 21/35 with Eanx50 and O2:
Buhlmann ZHL-16B
50/80 (from Deco Planner 3.1.4):
170', 25min;
(ascent rate 30'/min);
70', 1min (Eanx50);
60', 1min;
50', 2min;
40', 2min;
30', 5min;
20', 10min (Oxygen);
10', 6min -->same as slow 3 foot per min ascent to surface on O2.
And how many deco dives do you plan on doing over how many days?
Finally and most important, where is the nearest recompression chamber that will treat emergency diving accidents 24/7? (There's NEDU in Panama City, but the Navy might only treat civilian casualties as a last resort). . .
