What's the use?
- Thread starter OceanMist333
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Did anyone ask OceanMist333 if he's just using a computer?
mrfixitchapman
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Howard ruined it for the rest of us.
DC
DC
ScubaInChicago
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I think you being a little rough on OceanMist333. If I remember correctly Deon Dreyer made it all the way down to 876 feet at Bushmans hole on a single tank.... Oh wait, he was dead...free equipment, but who would want it if he pays as much attention to it as he does his tables.
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ALL dives are gas limited - some more than others. What are y'all talking about? I'm a air hog, but I've gotten into deco on the first dive using Nitrox in 120 cf tank because I stayed until low. If I can do that, anyone was get into deco on one dive with a large enough tank.
I think the original troll must have cheated on his training.
Hmmm....just a thought here but I would never have seen this thread this morning except for people bumping it with "please don't feed the troll" messages. If you really think the guy is a troll and/or have nothing useful to contribute, just stop posting. Out of 8000 posts I don't think I've ever seen the need for a "don't feed the troll" message.
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The OP's theory is pretty sound and was common practice in the past. The original steel 72 and to a slightly lesser extent the AL 80 (77 cu ft of gas) were popular because it was considered to be very difficult for most people to get bent on a single tank of gas in a single 12 hour period of time.
At some point a hundred or dives into my career I explored this with the US Navy tables in use by everyone at the time and my SAC rate. I found that I was indeed gas limited on a single dive to any depth down to 90 ft with a 500 psi reserve with a steel 72. At 100 ft a steel 72 had enough gas to let me overstay the 20 minute NDL on a square profile. So in effect, the limited tank capacity served as a fairly efficient multilevel computer at depths of 90 feet or less as long as you did the deepest portion of the dive first.
Lots of divers dove that way in the mid 1980's when I started diving. Plus if you look at the US Navy air decompression tables, you will note that adding a 5 minute deco stop extends the NDL's even further, so in effect a 5 minute "safety" stop covered all sorts of deco sins and 7 minutes pushes it even farther.
Now...the disclaimer is that there were some differences between then and now. The US Navy tables were not very conservative, everyone dove air and the majority of divers were in a lot better shape then than the majority of divers are now and repetitive dives were not quite as common (A hit rate of about 1% was acknowledged on square profiles for repetitive dives on the US navy tables - which was why no one with a brain ever dove square profiles and often fudged with next deeper time or depth or next deepr time and depth when using the tables, especially when doing repetitive dives.)
Tables used today are much more conservative and change the relationship between NDLs and gas limits - greatly reducing the depth limit where a single tank will be the limiting factor.
Tanks larger than 72 or 77 cu ft are frequently used today and this further changes the relationship. For example a steel 72 filled to the non plus rated service pressure of 2250 psi holds only 65 cu ft. But a single 130 holds exactly twice that capacity taking it into the realm of double tanks in terms of gas volume and deco potential.
Nitrox has had a major impact on the sport and also impacts the relationship between NDL and gas volume limits - but in the other direction - increasing the NDLs and increasing the depth where an NDL may take priority over gas volume in the dive plan.
Finally, dive computers were not available then, and neither were multi level tables, so there were no other options. Today, with dive computers being available and being available for maybe $100 used on e-bay, there is not much reason not to have one and to not use one.
But in effect, what the OP suggests still works in the broad sense of the word. If you know your own gas limits with regard to the NDLs for a single dive per day for your specific tank size and gas mix, and follw the basic reules regarding deepest portion first, no sawtooths, slow ascent rates and safety stops, you can pretty much do the dive by not exceeding the max depth you calculated, add a deep stop and a 5 minute safety stop and probably dive safely for the rest of your career. But the reality is, you are still using the dive tables to develop that knowledge of your personal limits even if you do not bring them along on the actual dive.
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Deco is also not a 100% sure thing. A diver's deco requirements vary from diver to diver and from day to day in addition to being impacted by workload, water temp, etc. A diver's best indicator of whether the deco they are doing is effective is how they feel after a dive. If a diver is feeling fatigued, achy or flu like after a dive or a weekend of diving, the odds are they need to change their decompression practices. In my case I found that after most wekeends of 2-3 divers per day - many of them well below 100 ft, that I often felt fatigued and sometimes flu like on monday morning even though I stayed within the table or computer limits.
When I started doing deep stops followed by slower ascents with 1 minute stops at 40 ft, and 30 feet prior to the usual 5 min safety stop at 20 ft with a very slow ascent from there to the surface, I felt fine. I also found a similar improvement with an accellerated deco gas on deco dives when that became common practice.
So in effect if you feel bad after a dive, you need to do more deco, use slower ascent rates, reduce saw tooths, avoid reverse profiles, etc until you feel better post dive. If you still feel bad even after improving the quality of your deco, you need to consider quitting the sport and taking up knitting, golf, bowling or something.
----
The OP's theory is pretty sound and was common practice in the past. The original steel 72 and to a slightly lesser extent the AL 80 (77 cu ft of gas) were popular because it was considered to be very difficult for most people to get bent on a single tank of gas in a single 12 hour period of time.
At some point a hundred or dives into my career I explored this with the US Navy tables in use by everyone at the time and my SAC rate. I found that I was indeed gas limited on a single dive to any depth down to 90 ft with a 500 psi reserve with a steel 72. At 100 ft a steel 72 had enough gas to let me overstay the 20 minute NDL on a square profile. So in effect, the limited tank capacity served as a fairly efficient multilevel computer at depths of 90 feet or less as long as you did the deepest portion of the dive first.
Lots of divers dove that way in the mid 1980's when I started diving. Plus if you look at the US Navy air decompression tables, you will note that adding a 5 minute deco stop extends the NDL's even further, so in effect a 5 minute "safety" stop covered all sorts of deco sins and 7 minutes pushes it even farther.
Now...the disclaimer is that there were some differences between then and now. The US Navy tables were not very conservative, everyone dove air and the majority of divers were in a lot better shape then than the majority of divers are now and repetitive dives were not quite as common (A hit rate of about 1% was acknowledged on square profiles for repetitive dives on the US navy tables - which was why no one with a brain ever dove square profiles and often fudged with next deeper time or depth or next deepr time and depth when using the tables, especially when doing repetitive dives.)
Tables used today are much more conservative and change the relationship between NDLs and gas limits - greatly reducing the depth limit where a single tank will be the limiting factor.
Tanks larger than 72 or 77 cu ft are frequently used today and this further changes the relationship. For example a steel 72 filled to the non plus rated service pressure of 2250 psi holds only 65 cu ft. But a single 130 holds exactly twice that capacity taking it into the realm of double tanks in terms of gas volume and deco potential.
Nitrox has had a major impact on the sport and also impacts the relationship between NDL and gas volume limits - but in the other direction - increasing the NDLs and increasing the depth where an NDL may take priority over gas volume in the dive plan.
Finally, dive computers were not available then, and neither were multi level tables, so there were no other options. Today, with dive computers being available and being available for maybe $100 used on e-bay, there is not much reason not to have one and to not use one.
But in effect, what the OP suggests still works in the broad sense of the word. If you know your own gas limits with regard to the NDLs for a single dive per day for your specific tank size and gas mix, and follw the basic reules regarding deepest portion first, no sawtooths, slow ascent rates and safety stops, you can pretty much do the dive by not exceeding the max depth you calculated, add a deep stop and a 5 minute safety stop and probably dive safely for the rest of your career. But the reality is, you are still using the dive tables to develop that knowledge of your personal limits even if you do not bring them along on the actual dive.
-----
Deco is also not a 100% sure thing. A diver's deco requirements vary from diver to diver and from day to day in addition to being impacted by workload, water temp, etc. A diver's best indicator of whether the deco they are doing is effective is how they feel after a dive. If a diver is feeling fatigued, achy or flu like after a dive or a weekend of diving, the odds are they need to change their decompression practices. In my case I found that after most wekeends of 2-3 divers per day - many of them well below 100 ft, that I often felt fatigued and sometimes flu like on monday morning even though I stayed within the table or computer limits.
When I started doing deep stops followed by slower ascents with 1 minute stops at 40 ft, and 30 feet prior to the usual 5 min safety stop at 20 ft with a very slow ascent from there to the surface, I felt fine. I also found a similar improvement with an accellerated deco gas on deco dives when that became common practice.
So in effect if you feel bad after a dive, you need to do more deco, use slower ascent rates, reduce saw tooths, avoid reverse profiles, etc until you feel better post dive. If you still feel bad even after improving the quality of your deco, you need to consider quitting the sport and taking up knitting, golf, bowling or something.
ucfdiver
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