Geezer Gas

[GrumpyOldGuy]

No real argument from me. Personally I do the math and then check it against a rather long history of actual dives, so I know precisely how much gas to allow for ascent. It's mainly allowing a buffer for stress and a buddy that adds some guessing. Dive plans can be as simple as max depth is xx, turn at xx and ascend at xx . The can also be as complex as you want.

The question arose from a suggestion the nitrox was safer because you are more likely to hit you gas limit before you NDL limit. I threw a flag suggesting this was not good planning because it variable depending many other items. Personally, I almost always hit NDL before gas unless its a shallow shore dive. My thoughts are if you need a buffer on NDL, plan it. By keeping your computer out of the caution zone, you are essentially doing this.

Not everyone agrees with me, no problem.

 

[BRT]

No real argument from me. Personally I do the math and then check it against a rather long history of actual dives, so I know precisely how much gas to allow for ascent. It's mainly allowing a buffer for stress and a buddy that adds some guessing. Dive plans can be as simple as max depth is xx, turn at xx and ascend at xx . The can also be as complex as you want.

The question arose from a suggestion the nitrox was safer because you are more likely to hit you gas limit before you NDL limit. I threw a flag suggesting this was not good planning because it variable depending many other items. Personally, I almost always hit NDL before gas unless its a shallow shore dive. My thoughts are if you need a buffer on NDL, plan it. By keeping your computer out of the caution zone, you are essentially doing this.

Not everyone agrees with me, no problem.

Do you hit NDL's before gas even in the 100' range with 32%? I have been surprised at the difference in Cozumel where we can hit 100-110' and then work our way up to 50' or so. The dives went from NDL limited to air limited or just limited by running out of reef as it dropped away below us. 2nd dives on 36% at 60 or so feet just go on and on.

 

[NAM001]

Planning should not be that difficult. Especially for the simple rec dives. I really dont know any one that is that anal about planning. Granted the degree is site specific. MOst dives for me go this way. We start deep adn see stuff till we get to 2/3 tank. first one at 2/3 and we head up to a shallower depth and resume enjoying the dive till we get say 1000 psi and look around and see what line is potentially growing to get to the boat. If the heard is starting to circle and we have lots of air we go up last. If we are under 750# we try to get up first and out of the way and get the best drinks in the cooler. I think too many times we try to make this too difficult. Planning for the worse is not a bad thing but when the dive is to 50 ft just what is the worse. Not every dive is a 120' dive with a short filled al 80. I tend to do what storker does i watch the ndl and air psi and modify the dive on the fly. Works well on drift dives or in general sightseeing dives. Clearly the rules have to be more stringent for a deep or wreck dive and even more so on a penatration dive. For me using the worse case rules for the easiest dives is not rational. right tool for the job and the right plan method for the right dive. I dont plan to have gas available for deco on a 30 ft dive. Still the consistant aspect is still ,,,, the diver with the worst situation drives the dive.

 

[Storker]

MOst dives for me go this way. We start deep adn see stuff till we get to 2/3 tank. first one at 2/3 and we head up to a shallower depth and resume enjoying the dive till we get say 1000 psi and look around and see what line is potentially growing to get to the boat. If the heard is starting to circle and we have lots of air we go up last.

Most - or, rather, almost all - of my dives require me to give my planned run time to the dive leader, and I'd better surface no later than that. Which means I do a bit of planning above and beyond the "splash, muck around, surface at 50 bar" level.

On air, I'm NDL limited on a square profile deeper than about 20m, but I hardly ever dive square profiles. It's almost always sloping bottoms or walls, and then I always plan a multilevel profile allowing me to surface with (or at least start my safety stop at) 50 bar and fairly close to the NDL.


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[KenGordon]

I like Nitrox and use it for all non trivial dives when available. I regard it as insurance. A dive has some risk throughout, not just at the end (whether due to limits of decompression or gas). Part of that risk is the consequences of a rapid ascent, that will be mitigated by the use of nitrox. As the dive is extended up to the decompression limit the instantaneous ascent/deco risk converges with that of an air dive but is never worse. So your average risk exposure will be lower.

 

[NAM001]

Sounds like boat ops are very different. Most places that, that are not 30' local lakes, are available to me have nice flat bottoms . I can go the the flower gardens and yes there is a wall but other than that its open range of 80-100 ft. We have perhaps 20 divers int he water at the same time. No one really cares how long you are gone. The boat ops do check your max depth and ending PSI when you get on board the record it and use that data to determine when its time to say XXXXX has been down too long. Many times i have been asked how many are waiting to get onboard. I look down and see perhaps 6 still in the water and if that accounts for everyone, all is well. We have never came up with a short count. The gardens boat I used issues a tag for each diver. Each diver is a number and not a name. time in and out with PSI is recorded. the crew determines the SI based one the worse case diver. Most times you can look 100' dodwn to the bottom and see the divers still down. So its a different environment I am sure. Then there are night dives that are easier yet to keep track of the divers still down. Yea I love gulf diving when i can.

Most - or, rather, almost all - of my dives require me to give my planned run time to the dive leader, and I'd better surface no later than that. Which means I do a bit of planning above and beyond the "splash, muck around, surface at 50 bar" level.

On air, I'm NDL limited on a square profile deeper than about 20m, but I hardly ever dive square profiles. It's almost always sloping bottoms or walls, and then I always plan a multilevel profile allowing me to surface with (or at least start my safety stop at) 50 bar and fairly close to the NDL.


--
Sent from my Android phone
Typos are a feature, not a bug

 

[Storker]

Sounds like boat ops are very different.

No surprise

My diving is most often club diving, but also boat ops (who basically provide a taxi ride and a site briefing) ask you to give a maximum run time. I guess it's a regional/national culture, since a lot of Nordic diving is with nonprofit clubs associated with the CMAS through the national diving association, not commercial ops. For those clubs, max depth and max time is the minimum you have to give to the dive leader before you splash. And if you don't show up at the time you're supposed to (including protocol for buddy separation), you might find a full-blown rescue operation when you eventually surface.

Also, we don't have coral reefs up here. Even when boat diving, you very often anchor fairly close to shore, or a small island/skerry, or a shallow rock reef. In such places, you more often than not have a sloping bottom, so the majority of sites are very well suited for multilevel dives and different personal depth limits.

No one really cares how long you are gone.

That actually sounds a bit scary to me.

 

[NAM001]

It gets even "More scarry." No one keeps track of buddies either. You splash and you get out. Often buddies are swapped at depth based on gas supply. I would guess that probably 70% or more on boats are insta buddies. By the 3rd dive or so some sort of recognizable buddy system exists as you find who has similar gas consumptions to thiers. Definately not a portocol to use in the north atlantic. But it works fine in the gulf areas i have used. Many of the vacation divers are the first to get back on board with <500 when the rest of us have 2/3 tank left. I uspect that you dont have these issues in your area to contend with. I have seen a vacation diver go through 2500 psi just getting to the bottom of the anchor line, and tehnext dive go ooa at 80'. You get him up to the boat turn him over to the crew and you go back down. You dont spend 4-600 dollars for 2-3 days diving and limit your self to 15 min dives. when you can get a dozen 40 - 60 min or longer dives in the 2-3 days. Any way we are probably off the subject of geezer gas.

No surprise

My diving is most often club diving, but also boat ops (who basically provide a taxi ride and a site briefing) ask you to give a maximum run time. I guess it's a regional/national culture, since a lot of Nordic diving is with nonprofit clubs associated with the CMAS through the national diving association, not commercial ops. For those clubs, max depth and max time is the minimum you have to give to the dive leader before you splash. And if you don't show up at the time you're supposed to (including protocol for buddy separation), you might find a full-blown rescue operation when you eventually surface.

Also, we don't have coral reefs up here. Even when boat diving, you very often anchor fairly close to shore, or a small island/skerry, or a shallow rock reef. In such places, you more often than not have a sloping bottom, so the majority of sites are very well suited for multilevel dives and different personal depth limits.


That actually sounds a bit scary to me.

 

[MaxBottomtime]

I like Nitrox and use it for all non trivial dives when available. I regard it as insurance. A dive has some risk throughout, not just at the end (whether due to limits of decompression or gas). Part of that risk is the consequences of a rapid ascent, that will be mitigated by the use of nitrox.

What I've learned from this thread;
Nitrox contains a magical ingredient that not only gives you more energy, it relieves headaches and now allows for rapid ascents. I'm shocked that none of this is covered in the nitrox courses.

 

[KenGordon]

What I've learned from this thread;
Nitrox contains a magical ingredient that not only gives you more energy, it relieves headaches and now allows for rapid ascents. I'm shocked that none of this is covered in the nitrox courses.

Many nitrox courses include equivalent air depths. Which is more likely to lead to DCS, going directly to the surface from 25m or from 30m?