Posted by northcoast diver on February 17, 2005 at 18:55:44:
In Reply to: Re: You love to bring Admiral Linda up posted by Chuck Tribolet on February 17, 2005 at 16:21:59:
Since it sounds from your post like you are therefore diving tanks again Chuck, let me explain how best mix determinations work.
If you are diving NDL, then the best mix is that mix that gives you the least risk of violating your NDL times. Air is the best mix at 20 ft depth, since you can dive forever on air at 20 ft and ascend to the surface anytime you want to. This mix (air) is good for scrubbing boat bottoms, for sure.
Any deeper than 20 ft, and your diving results in an NDL limit of some kind. The deeper your depth, the shorter your NDL time. You might think that nitrox at any depth is a good mix since it reduces your effective equivalent air depth. However since you will never bump up against your NDL times for air with a single 80 cu ft tank and a normal RMV/SCR of around 75 cu ft per min working, then the advantage that nitrox gives you when shallower than 65 feet is insignificant. Because:
DIVE PLAN #1
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 3
Dec to 65ft (1) on Air, 50ft/min descent.
Level 65ft 28:42 (30) on Air, 0.62 ppO2, 65ft ead
Asc to 20ft (31) on Air, -30ft/min ascent.
Asc to 15ft (31) on Air, -30ft/min ascent.
Asc to sfc. (32) on Air, -30ft/min ascent.
OTU's this dive: 9
CNS Total: 4.4%
69.0 cu ft Air
69 cu ft TOTAL
DIVE PLAN #2
Surface interval = 0 day 1 hr 0 min.
Elevation = 0ft
Conservatism = + 3
Dec to 65ft (1) on Air, 50ft/min descent.
Level 65ft 28:42 (30) on Air, 0.62 ppO2, 65ft ead
Asc to 20ft (31) on Air, -30ft/min ascent.
Asc to 15ft (31) on Air, -30ft/min ascent.
Asc to sfc. (32) on Air, -30ft/min ascent.
OTU's this dive: 9
CNS Total: 7.1%
69.0 cu ft Air
69 cu ft TOTAL
DIVE PLAN #3
Surface interval = 0 day 1 hr 0 min.
Elevation = 0ft
Conservatism = + 3
Dec to 65ft (1) on Air, 50ft/min descent.
Level 65ft 28:42 (30) on Air, 0.62 ppO2, 65ft ead
Asc to 20ft (31) on Air, -30ft/min ascent.
Asc to 15ft (31) on Air, -30ft/min ascent.
Asc to sfc. (32) on Air, -30ft/min ascent.
OTU's this dive: 9
CNS Total: 8.9%
69.0 cu ft Air
69 cu ft TOTAL
DIVE PLAN #4
Surface interval = 0 day 1 hr 0 min.
Elevation = 0ft
Conservatism = + 3
Dec to 65ft (1) on Air, 50ft/min descent.
Level 65ft 28:42 (30) on Air, 0.62 ppO2, 65ft ead
Asc to 20ft (31) on Air, -30ft/min ascent.
Asc to 15ft (31) on Air, -30ft/min ascent.
Asc to sfc. (32) on Air, -30ft/min ascent.
OTU's this dive: 9
CNS Total: 10.0%
69.0 cu ft Air
69 cu ft TOTAL
DIVE PLAN #5
Surface interval = 0 day 1 hr 0 min.
Elevation = 0ft
Conservatism = + 3
Dec to 65ft (1) on Air, 50ft/min descent.
Level 65ft 28:42 (30) on Air, 0.62 ppO2, 65ft ead
Asc to 20ft (31) on Air, -30ft/min ascent.
Asc to 15ft (31) on Air, -30ft/min ascent.
Asc to sfc. (32) on Air, -30ft/min ascent.
OTU's this dive: 9
CNS Total: 10.7%
69.0 cu ft Air
69 cu ft TOTAL
You never ever bump up against a deco requirement as long as you keep your depth on air shallower than 65 ft, with a normal scuba tank (read: 80 cu ft), and a normal RMV/SCR (not your pretty mousie girlfriend's but your own), together with 1 hour minimal surface interval times. You can therefore dive on air to 65 ft or shallower for as many dives as you want. Stay off the liquor, avoid the caffeine, stay hydrated, get plenty of rest at night, and you should not trigger any DCI symptoms for yourself.
For diving deeper than 65 ft, the best mix goal would be to get your equivalent air depth to 65 ft or less with nitrox. That gives you the same benefits as would keeping your depth to 65 ft or shallower on air.
EAN 35 reduces your equivalent air depth at 100 ft to 65 ft. And it allows you to dive to 100 ft while keeping your ppO2 to 1.4 . That makes it the best mix for all of your diving in the range of 70 to 100 ft. And therefore with a normal sized scuba tank, and normaly RMV/SCR, together with 1 hour minimum surface intervals, you can dive as much as you want to 100 ft with EAN35. Ergo:
DIVE PLAN #1
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 3
Dec to 100ft (2) on Nitrox 35.0, 50ft/min descent.
Level 100ft 20:00 (22) on Nitrox 35.0, 1.41 ppO2, 76ft ead
Asc to 70ft (23) on Nitrox 35.0, -30ft/min ascent.
Asc to 20ft (24) on Nitrox 50.0, -30ft/min ascent.
Asc to 15ft (24) on Nitrox 50.0, -30ft/min ascent.
Asc to sfc. (25) on Nitrox 50.0, -30ft/min ascent.
OTU's this dive: 38
CNS Total: 15.2%
66.8 cu ft Nitrox 35.0
3.6 cu ft Nitrox 50.0
70.4 cu ft TOTAL
DIVE PLAN #2
Surface interval = 0 day 1 hr 0 min.
Elevation = 0ft
Conservatism = + 3
Dec to 100ft (2) on Nitrox 35.0, 50ft/min descent.
Level 100ft 20:00 (22) on Nitrox 35.0, 1.41 ppO2, 76ft ead
Asc to 20ft (24) on Nitrox 35.0, -30ft/min ascent.
Asc to 15ft (24) on Nitrox 35.0, -30ft/min ascent.
Asc to sfc. (25) on Nitrox 35.0, -30ft/min ascent.
OTU's this dive: 37
CNS Total: 24.3%
70.4 cu ft Nitrox 35.0
70.4 cu ft TOTAL
DIVE PLAN #3
Surface interval = 0 day 1 hr 0 min.
Elevation = 0ft
Conservatism = + 3
Dec to 100ft (2) on Nitrox 35.0, 50ft/min descent.
Level 100ft 20:00 (22) on Nitrox 35.0, 1.41 ppO2, 76ft ead
Asc to 20ft (24) on Nitrox 35.0, -30ft/min ascent.
Asc to 15ft (24) on Nitrox 35.0, -30ft/min ascent.
Asc to sfc. (25) on Nitrox 35.0, -30ft/min ascent.
OTU's this dive: 37
CNS Total: 30.0%
70.4 cu ft Nitrox 35.0
70.4 cu ft TOTAL
DIVE PLAN #4
Surface interval = 0 day 1 hr 0 min.
Elevation = 0ft
Conservatism = + 3
Dec to 100ft (2) on Nitrox 35.0, 50ft/min descent.
Level 100ft 20:00 (22) on Nitrox 35.0, 1.41 ppO2, 76ft ead
Asc to 20ft (24) on Nitrox 35.0, -30ft/min ascent.
Asc to 15ft (24) on Nitrox 35.0, -30ft/min ascent.
Asc to sfc. (25) on Nitrox 35.0, -30ft/min ascent.
OTU's this dive: 37
CNS Total: 33.6%
70.4 cu ft Nitrox 35.0
70.4 cu ft TOTAL
DIVE PLAN #5
Surface interval = 0 day 1 hr 0 min.
Elevation = 0ft
Conservatism = + 3
Dec to 100ft (2) on Nitrox 35.0, 50ft/min descent.
Level 100ft 20:00 (22) on Nitrox 35.0, 1.41 ppO2, 76ft ead
Asc to 20ft (24) on Nitrox 35.0, -30ft/min ascent.
Asc to 15ft (24) on Nitrox 35.0, -30ft/min ascent.
Asc to sfc. (25) on Nitrox 35.0, -30ft/min ascent.
OTU's this dive: 37
CNS Total: 35.9%
70.4 cu ft Nitrox 35.0
70.4 cu ft TOTAL
You never ever bump up against a decompression limit, on EAN 35 to 100 ft, same as for air to 65 ft.
You can leave your dive computer at home, if you stop diving the worst mixes and switch to the best mix for whatever your planned depth is going to be.
Now I know youre not a rocket scientist Chuck, but this should even make some sense to you. Even you.
Dive computers are great toys. They help brand new divers who are not nitrox certified yet learn how to dive on air. But in the long term they are an unnneded item. And their algorithms are simply and exercise in the futility of copiing with a bad mix decision in your dive planning.
I hope you and Linda get married someday soon. You two make such a cute couple. You are so tall and lankey, if graying. And she is to petite and cute as a bunny.