You are correct. Every one should have a gas plan of some sorts. Normally it not a formal plan but more like a rule of thumb that dies not incumber the dive. I use 1000 psi from 100 ft and then 600 from 60 or less. Those numbers are not necessarily for my consumption it is for those that have higher sac's whom i am buddied with. For those that have no context of what rock bottom is, (brand newby ow divers) the amount of air you suggest becomes a threat to them doing deeper dives. Mostly so based on what they do not know about rock bottom and how it applied to them. Very much like a street light turning red with no traffic raising your pulse and preventing your feet from leaving the curb. My wife asked me the other day why in a 25 foot lake we dont ascent 10 feet and wait one minute and repeat till on the surface. We had to sit down and have that talk, (deco, rec and tech.). Her eyes started getting buggy and then nearly blew from the socket when i offered to expand the conversation to gradient factors and ratio deco. She said "One question,,,,,,, am I ok doing 30 ft per minute like they told me in class? I said yes, she said ,,,then for now nothing else matters. As far as the basics of OW's going past 60' , you have some very good points.
Changed depth limit for PADI Open Water
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Kevrumbo
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Example Gas Planning for the Basic OW 18m/60' Limit
2 bar/min is same as 29psi/min;
5.6 bar/min is 81psi/min.
Easy imperial US/metric conversions for depth & pressure, that you can do in your head:
Depth in meters multiplied by 10/3 gives depth in feet;
Feet multiplied by 3/10 gives meters.
Example: 18m(10/3) = 60' ; 60'(3/10) = 18m
Pressure bar multiplied by 3/2, and multiplied again by 10 gives pressure psi;
Pressure psi multiplied by 2/3, and divided by 10 gives pressure bar.
Ex): 200bar(3/2)(10) = 3000psi ; 3000psi(2/3)/10 = 200bar.
. . .
Here's another Emergency gas planning example & exercise for the OP, for a dive to the Basic Open Water Limit of 18m/60':
Emergency "Stressed" 28 litres/min SCR (Surface Consumption Rate, also referred to as SAC), with 18 meters (2.8 ATA) depth NDL, and with an arbitrarily conservative one minute stop every 3 meters to surface [can be done as a 30sec hold at depth followed with a 30sec ascent time to the next 3m delta stop depth -in other words use 30sec hold & 30sec ascent intervals all the way to the surface]:
2.8 x 28 x 1 = 78.4
2.5 x 28 x 1 = 70
2.2 x 28 x 1 = 61.6
1.9 x 28 x 1 = 53.2
1.6 x 28 x 1 = 44.8
1.3 x 28 x 1 = 36.4
1.0 x 28 x 1 = 28
Sum Total: 372.4 litres gas needed to ascend to surface for an emergency contingency.
Divide the above total by the metric tank rating of the Scuba cylinder in use; for this example let's use the AL80 tank again which has a metric rating of 11 litres/bar. So 372/11 = approx 35 bar.
That's 35 bar to get you to the surface --to get yourself and sharing gas with an Out-of-Air Buddy you will need at least twice this amount: 35 x 2 = 70 bar. Therefore your Rock Bottom Reserve is 70 bar showing on your SPG --if there is no emergency air sharing contingency at that instant, just continue the dive but start a easy nominal ascent to the shallower depths between 5m and 9m. Finally, be at your 5m safety stop with your buddy with no less than 50 bar showing on the SPG.
Your usable gas for the dive is your starting pressure subtracted by the Rock Bottom Reserve --so 200 bar minus 70 bar equals 130 bar usable. Let's use 20 bar of this 130 to get squared away in good trim & buoyancy on the descent to 18m which leaves 110 bar usable. Now if your dive plan calls for returning to near the vicinity of your original point of entry (like a beach dive for instance), then turn the dive back around when you use half of 110 bar or 55 bar consumed.
So for a nominal dive with an SCR of 22 litres/min on a 11L (AL80) tank, your resulting pressure SCR will be 2 bar/min [22 divided-by 11 equals 2bar/min]. Your depth in meters, which converts easily to ATA (simply divide-by-10 and add 1) becomes your multiplier depth factor for your 2bar/min pressure SCR.
18 meters depth is 2.8 ATA (divide 18 by 10 and add 1 equals 2.8); your 2bar/min SCR at depth -or Depth Consumption Rate (DCR)- now becomes 5.6 bar/min. [2.8 times 2bar/min equals 5.6 bar/min]. So 10 minutes at depth 18m on an AL80 (11L/bar) tank in nominal conditions, you would expect to consume 56bar of gas (10min times 5.6 bar/min equals 56bar) and your SPG reading to show a delta down of 56bar. . .
Okay, you splash in to start the dive with 200bar and a 70bar rock bottom. You use up 20bar on descent --initial exertion, inflating your wing etc. -so you now have 180bar with 70bar rock bottom at present depth 18m, a net usable of 110bar (180 minus 70 is 110). Finning out for 10 minutes, an easy swim looking at all the cool marine life around -- you already know by the end of this 10 minute interval that you've used up 56bar (see previous paragraph above), so you decide to turn the dive. You should now know you have roughly 50bar of usable gas left before encroaching on your Rock Bottom Reserve, and realize that you must start a nominal ascent within the next 10 minute interval. Alright, so while turning back, you see a turtle and decide to chase it for a few minutes, huffing & puffing on your reg, until it dives down below your operational depth of 18m; you immediately check your SPG and it reads 70bar --bingo! Rock bottom has arrived so start ascending to the shallower depths . . .or if your Buddy just happens to blow his tank neck O-ring at that instant --you know you've got plenty of breathing gas margin for a controlled air-sharing Emergency ascent profile as described above. . .
Be aware that depending on environmental conditions and physical exertion (cold water, stiff current, long surface swim, heavy workload at depth etc), you may have to reserve a greater Rock Bottom Reserve --perhaps as high or even over 100 bar on the 11L/AL80 tank to be conservative. (Even better just abort the dive, wait another day or find another easier site to dive!)
____
Notes for American Divers using US Imperial Units:
Stressed SCR of 28 litres/min is equivalent to 1 cuft/min;
Nominal SCR of 22 litres/min is approx 0.75 cuft/min;
Here's another Emergency gas planning example & exercise for the OP, for a dive to the Basic Open Water Limit of 18m/60':
Emergency "Stressed" 28 litres/min SCR (Surface Consumption Rate, also referred to as SAC), with 18 meters (2.8 ATA) depth NDL, and with an arbitrarily conservative one minute stop every 3 meters to surface [can be done as a 30sec hold at depth followed with a 30sec ascent time to the next 3m delta stop depth -in other words use 30sec hold & 30sec ascent intervals all the way to the surface]:
2.8 x 28 x 1 = 78.4
2.5 x 28 x 1 = 70
2.2 x 28 x 1 = 61.6
1.9 x 28 x 1 = 53.2
1.6 x 28 x 1 = 44.8
1.3 x 28 x 1 = 36.4
1.0 x 28 x 1 = 28
Sum Total: 372.4 litres gas needed to ascend to surface for an emergency contingency.
Divide the above total by the metric tank rating of the Scuba cylinder in use; for this example let's use the AL80 tank again which has a metric rating of 11 litres/bar. So 372/11 = approx 35 bar.
That's 35 bar to get you to the surface --to get yourself and sharing gas with an Out-of-Air Buddy you will need at least twice this amount: 35 x 2 = 70 bar. Therefore your Rock Bottom Reserve is 70 bar showing on your SPG --if there is no emergency air sharing contingency at that instant, just continue the dive but start a easy nominal ascent to the shallower depths between 5m and 9m. Finally, be at your 5m safety stop with your buddy with no less than 50 bar showing on the SPG.
Your usable gas for the dive is your starting pressure subtracted by the Rock Bottom Reserve --so 200 bar minus 70 bar equals 130 bar usable. Let's use 20 bar of this 130 to get squared away in good trim & buoyancy on the descent to 18m which leaves 110 bar usable. Now if your dive plan calls for returning to near the vicinity of your original point of entry (like a beach dive for instance), then turn the dive back around when you use half of 110 bar or 55 bar consumed.
So for a nominal dive with an SCR of 22 litres/min on a 11L (AL80) tank, your resulting pressure SCR will be 2 bar/min [22 divided-by 11 equals 2bar/min]. Your depth in meters, which converts easily to ATA (simply divide-by-10 and add 1) becomes your multiplier depth factor for your 2bar/min pressure SCR.
18 meters depth is 2.8 ATA (divide 18 by 10 and add 1 equals 2.8); your 2bar/min SCR at depth -or Depth Consumption Rate (DCR)- now becomes 5.6 bar/min. [2.8 times 2bar/min equals 5.6 bar/min]. So 10 minutes at depth 18m on an AL80 (11L/bar) tank in nominal conditions, you would expect to consume 56bar of gas (10min times 5.6 bar/min equals 56bar) and your SPG reading to show a delta down of 56bar. . .
Okay, you splash in to start the dive with 200bar and a 70bar rock bottom. You use up 20bar on descent --initial exertion, inflating your wing etc. -so you now have 180bar with 70bar rock bottom at present depth 18m, a net usable of 110bar (180 minus 70 is 110). Finning out for 10 minutes, an easy swim looking at all the cool marine life around -- you already know by the end of this 10 minute interval that you've used up 56bar (see previous paragraph above), so you decide to turn the dive. You should now know you have roughly 50bar of usable gas left before encroaching on your Rock Bottom Reserve, and realize that you must start a nominal ascent within the next 10 minute interval. Alright, so while turning back, you see a turtle and decide to chase it for a few minutes, huffing & puffing on your reg, until it dives down below your operational depth of 18m; you immediately check your SPG and it reads 70bar --bingo! Rock bottom has arrived so start ascending to the shallower depths . . .or if your Buddy just happens to blow his tank neck O-ring at that instant --you know you've got plenty of breathing gas margin for a controlled air-sharing Emergency ascent profile as described above. . .
Be aware that depending on environmental conditions and physical exertion (cold water, stiff current, long surface swim, heavy workload at depth etc), you may have to reserve a greater Rock Bottom Reserve --perhaps as high or even over 100 bar on the 11L/AL80 tank to be conservative. (Even better just abort the dive, wait another day or find another easier site to dive!)
____
Notes for American Divers using US Imperial Units:
Stressed SCR of 28 litres/min is equivalent to 1 cuft/min;
Nominal SCR of 22 litres/min is approx 0.75 cuft/min;
2 bar/min is same as 29psi/min;
5.6 bar/min is 81psi/min.
Easy imperial US/metric conversions for depth & pressure, that you can do in your head:
Depth in meters multiplied by 10/3 gives depth in feet;
Feet multiplied by 3/10 gives meters.
Example: 18m(10/3) = 60' ; 60'(3/10) = 18m
Pressure bar multiplied by 3/2, and multiplied again by 10 gives pressure psi;
Pressure psi multiplied by 2/3, and divided by 10 gives pressure bar.
Ex): 200bar(3/2)(10) = 3000psi ; 3000psi(2/3)/10 = 200bar.
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The vast majority of active forum members are serious about diving and are willing and wanting to develop their skills. Most will agree that the current level of diver education is lacking and that the most basic concepts of planning and gas management could be readily be incorporated into beginner training. Whats even more ludicrous then posting all the maths showing the risks with deeper diving, is that AOW (at least PADI), doesn't teach gas planning at all - which was the OP's point, why need AOW to go deeper than 18m? In the PADI world's current education model, if you required this level of gas planning to dive to 30m, only Tec certified divers would qualify (I believe thats the first course where gas planning is really taught, correct me if i'm wrong).
Unfortunately we live in a world of overly casual divers and overzealous lawyers. Dive shops need simple criteria for the complex question of "who is qualified for the dive". I can see how strict rules allows dive shops to avoid debates with their customers. But at least pick a better criteria than AOW, the most meaningless card out there. I've seen shops that require a check dive. A little better, but what can you really evaluate other than buoyancy skills? I was in the Maldives last year, did a 10 day live aboard followed by 4 days at a resort. I looked into some resort diving, but was told I had to spend $300 and a whole day of check dives in a see-nothing lagoon before I could do a boat dive. They said "You are rusty and need to do a weight check in a new environment, when was your last dive?" "Yesterday, here in the maldives" I replied. Not a sufficient answer for them and I didn't waste any time or money diving.
Unfortunately we live in a world of overly casual divers and overzealous lawyers. Dive shops need simple criteria for the complex question of "who is qualified for the dive". I can see how strict rules allows dive shops to avoid debates with their customers. But at least pick a better criteria than AOW, the most meaningless card out there. I've seen shops that require a check dive. A little better, but what can you really evaluate other than buoyancy skills? I was in the Maldives last year, did a 10 day live aboard followed by 4 days at a resort. I looked into some resort diving, but was told I had to spend $300 and a whole day of check dives in a see-nothing lagoon before I could do a boat dive. They said "You are rusty and need to do a weight check in a new environment, when was your last dive?" "Yesterday, here in the maldives" I replied. Not a sufficient answer for them and I didn't waste any time or money diving.
Kevrumbo
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If you can competently & confidently demonstrate that you can derive a simple logical gas plan such as that above and show that you can follow it on a basic check-out dive --then along with presenting a logbook summary of your 25 years of diving experience (especially a large number of dives safely completed that are deeper than 18m), then you would have a fair claim to reciprocity of your original 1990 Open Water certification privilege to the 30m Max depth limit.
Unfortunately it is still up to the dive operator whether to honor that privilege or not, based on present day rules, regulations & standards as currently mandated and practiced by PADI.
archer1960
Contributor
When I was in Cozumel last year, I was newly certified OW with no dives beyond my certification requirements. The first day of boat diving was to ~85' IIRC, and they only wanted to see my OW card; they didn't care about anything beyond that. Later dives that same week went to 100' and slightly over (I hit 102). If I had wanted to, they would have let me do the Devil's Throat, which is a vertical shaft (cave) that starts at ~80 ft and goes down to 120 or so before it opens out on the side of the wall. I chose to skip that one because I wasn't sure how narc'd I would get and how I would react, but still ended the week with several dives between 60 and 85 ft, and the one dive to 102, on just an OW cert.
---------- Post added August 13th, 2015 at 10:04 AM ----------
For sure!
Stoo
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I'd hope that your logbook would supersede an ancient card. If it doesn't, I'd be inclined to look into a different dive operation. Like many of us "old-timers", we were certified before the "PADI-fication" of diving which requires a new course and card for every inch you move further into the sport.
AdivingBel
Diver
Sounds like they treated you as an adult diver capable of making informed decisions. I applaud you for acting as an adult diver and choosing to dive within your comfort level. Unless you told the DM (or shop) you weren't comfortable doing the deeper dives and were ignored, or the depths weren't mentioned in the pre-dive brief, I would dive with those guys again.
archer1960
Contributor
Sounds like they treated you as an adult diver capable of making informed decisions. I applaud you for acting as an adult diver and choosing to dive within your comfort level. Unless you told the DM (or shop) you weren't comfortable doing the deeper dives and were ignored, or the depths weren't mentioned in the pre-dive brief, I would dive with those guys again.
The dives always went exactly as briefed, which I guess isn't always the case. The group I was with last year is going to the same place (Scuba Club Cozumel) again this year, and if I had the money, I'd be with them in a heartbeat. The operation was very smooth and professional all week, and the DMs were terrific.
You said that padi does not teach that level of math for rock bottom. I believe you are right. It is my opinion that what AOW does is opens the eyes of OW;s to the complesities of diving deeper. They dont have to know how to compute rock bottom. They need to know that it exists and and tht recovery from a problem is not the same as at 25ft whre blow and go is still an option. The mere walk through of determining what rock bottom is ingrains to OWs that ulllike 30' you dont stay down till 600 and head up.
I keep hearing about how AOW cant teach everything. It is not designed to.. It is there as a make aware class so as to make you think about every dive. To remind them they are on their own and they are no longer on a trust me dive with the DM. Its no different than drivers ed and talking about following distance inreguards to speed and road conditions. You dont have to know how to compute stoping distancce on a wet road. You learn that if it is raining you double the following distance and use the in class math to drive the point home.
Even if the math is not gone through the actual dive and forcing gas psi monitoring is a personal demonstration of the effects of depth in real time.
---------- Post added August 14th, 2015 at 02:40 PM ----------
Please go on, explain to me what is so dinosour about stoo's comment. BTW i first certed in the late 60's when PADI was in the phase of a new born agency and what are we going to name it. The old timers did not mess things up. Its the newby's that have gone to the how to make the most $ of something simple. Its the newbys that require all methods to be instant gratification processes.
Story: 2 bulls standintg on a hill one old and one young. The younger says to the older "lets run down there and get us a couple of these. The older says let walk down and get them all.
If you are of the new generation you are handicapped because you cant conceive the past, you can only cuss it. We on the other side have not only seen the movie we were in it and most probably being laughed at cause our flippers do not match our masks.
On behalf of the younger generation, you do have so much more to manage when training is involved. cell phones candi crush texts ect. I can guarentee the old timers could assemble and tote their own gear and did not blame the dm when thier J valve was pulled. J valve ??? You can look that one up.
I get so much pleasure out of posts about when you are diving with an insta buddy you are diving solo. Why is that?
I keep hearing about how AOW cant teach everything. It is not designed to.. It is there as a make aware class so as to make you think about every dive. To remind them they are on their own and they are no longer on a trust me dive with the DM. Its no different than drivers ed and talking about following distance inreguards to speed and road conditions. You dont have to know how to compute stoping distancce on a wet road. You learn that if it is raining you double the following distance and use the in class math to drive the point home.
Even if the math is not gone through the actual dive and forcing gas psi monitoring is a personal demonstration of the effects of depth in real time.
---------- Post added August 14th, 2015 at 02:40 PM ----------
Please go on, explain to me what is so dinosour about stoo's comment. BTW i first certed in the late 60's when PADI was in the phase of a new born agency and what are we going to name it. The old timers did not mess things up. Its the newby's that have gone to the how to make the most $ of something simple. Its the newbys that require all methods to be instant gratification processes.
Story: 2 bulls standintg on a hill one old and one young. The younger says to the older "lets run down there and get us a couple of these. The older says let walk down and get them all.
If you are of the new generation you are handicapped because you cant conceive the past, you can only cuss it. We on the other side have not only seen the movie we were in it and most probably being laughed at cause our flippers do not match our masks.
On behalf of the younger generation, you do have so much more to manage when training is involved. cell phones candi crush texts ect. I can guarentee the old timers could assemble and tote their own gear and did not blame the dm when thier J valve was pulled. J valve ??? You can look that one up.
I get so much pleasure out of posts about when you are diving with an insta buddy you are diving solo. Why is that?
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