20 replies to this topic

[shadragon]

As I pick up more and more experience I am very glad I took my OW, ADV and subsequent courses from the shop I did. My ADV course had the night dive (Northern shop) and the deep dive was well past minimum standards. When I took my Deep course, we went to 123' and that stood as my personal depth record until very recently. We had a surplus of DM's on that course staging extra bottles with spare gas and 123' was the actual bottom. No way we could exceed it unless we dug. My point is they went beyond what the minimums were, challenged me and did so in a safe manner so we could get experience dealing with high gas consumption depths, narcosis and related factors.

Any dive is as challenging and technical as you want to make it. If the Oriskany flight is your goal, then work towards it. Dive the bridge superstructure first. I believe that is at 65' and I hear there is a lot to see just near the bridge. Your air will last a damn sight longer too at there. Then move lower gradually as you gain more experience. If it takes a few trips, so be it. I doubt the Oriskany is going anywhere so when you have the skills, knowledge and experience you can go to the flight deck @ 130. I would strongly suggest you take the Deep diver course and NITROX before that as well. When you have a couple of hundred dives under your belt, you start to realize just how little you really do know.

Get a buddy or buddies you trust, set a plan / schedule and move toward the goal in a methodical manner.

[shadragon]

The oxygen partial pressure of air is over 2.1 at that depth. (2.7 of a EaN 27%) So there is a significant likelyhood that there is no consumption. But if you assume a SAC rate of 1 then its bit less than 8 minutes.

Text book answer, but you negated to add the amount of gas needed for the ascent from that depth after eight minutes of bottom time or the obligatory deco time imposed by that profile. Add additional gas for your buddy, a bit more for a hard swim against the current to get back to the boat or other unexpected circumstances (just in case) and you will find a considerable amount of gas is required after your AL80 runs out. SAC rates look great on paper. Real life is somewhat different.

Oh and it was a trick question. Regular air at that depth will be well into the toxic range.

((309)/(33)+1)=9.08 ATA

ATA * O2% = PP02

(9.08) * (.21) = 1.9068

The general rule is a PP02 of 1.6 is absolute MAX. A safe PPO2 is about 1.2 - 1.3.

[DriftWood]

The oxygen partial pressure of air is over 2.1 at that depth. (2.7 of a EaN 27%) So there is a significant likelyhood that there is no consumption. But if you assume a SAC rate of 1 then its bit less than 8 minutes.

Text book answer, but you negated to add the amount of gas needed for the ascent from that depth after eight minutes of bottom time or the obligatory deco time imposed by that profile. Add additional gas for your buddy, a bit more for a hard swim against the current to get back to the boat or other unexpected circumstances (just in case) and you will find a considerable amount of gas is required after your AL80 runs out. SAC rates look great on paper. Real life is somewhat different.

Oh and it was a trick question. Regular air at that depth will be well into the toxic range.

((309)/(33)+1)=9.08 ATA

ATA * O2% = PP02

(9.08) * (.21) = 1.9068

The general rule is a PP02 of 1.6 is absolute MAX. A safe PPO2 is about 1.2 - 1.3.

I get the point about the toxicity, thus the comment about no consumption. And not to be picky but

((309 / 33) + 1) = 10.36 ATA

10.36 * .21 = 2.1763

[shadragon]

I get the point about the toxicity, thus the comment about no consumption. And not to be picky but

((309 / 33) + 1) = 10.36 ATA

10.36 * .21 = 2.1763

I like picky.

[WreckWench]

Tell me this? How long can you last on a cf 80 at 309ft?

Possibly not too long, and that wouldn't be down to his inexperience

That was OBVIOUSLY a typo! Good catch!

And great job on trying to figure out how long the cf 80 WOULD last if you tried to dive to 309ft!

[peterbj7]

Leaving aside the question of toxicity, I think there's a good chance the average diver wouldn't even get as far as 309ft on an 80. He sure as heck wouldn't get back again. Remember that SAC is purely theoretical, and under stress your gas consumption can rocket beyond what you might predict from your SAC. Consumption increased by a factor of 6 or even 8 is not unusual. That's why so many relatively experienced divers have died when attempting rescues or recoveries in adverse circumstances (not necessarily deep) when they have no training or experience in that very specialised discipline.

I had an "event" with a CCR at around that depth which caused me to go onto OC for maybe a couple of minutes. It was astonishing how rapidly I drained a 20 cf.ft. tank - from full to near empty in 3 or 4 minutes. Things happen very fast at extreme depth.