kydaka
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Also factor in the additional stress of an out of air situation and your SAC may double
500 psi for two divers?
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Basking Ridge Diver
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To leverage on what BoulderJohn said - I created my own personal MS-Excel sheet - the formulas in the posts above do you give you a start and you could build your own sheet with the calculations and play with it so you become familiar with how long the gas will last for you (based on your breathing rate, depth and time) - I have formulas that determine my descent, bottom and ascent which give me a fair idea of how much gas I would need. As you start creating it - it will cause you to ask more questions, do some research and in the end you can use it for a real dive to see how close you really do "Plan the Dive and Dive the Plan".
This is not required (building a spreadsheet) but if you really want to become better - the more you learn, investigate and discover the better you will be - and then you can go back your instructor and say - 500psi for 15 mins does not seem to work at 100 feet - but seems to work fine at 30 feet for me and the volume of gas I breath...
This is not required (building a spreadsheet) but if you really want to become better - the more you learn, investigate and discover the better you will be - and then you can go back your instructor and say - 500psi for 15 mins does not seem to work at 100 feet - but seems to work fine at 30 feet for me and the volume of gas I breath...
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You don't seriously believe that you're gonna keep your SAC rate when fit hits the shan? There's a reason you're supposed to double your (and your buddy's) SAC rate when you calculate rock bottom / min gas.
30 feet per second??? :dropmouth: You're gonna get bent and probably blow a few alveolas as well.
Actually, they are taught more than that, although they should be taught more.
This web site lists 145 agencies world wide offering introductory scuba certification. I could be wrong, but I believe a total of 2 of them teach rock bottom as a normal part of their instruction, and I am not sure those two certify more than a dozen new divers a year--if that. Most of the tech agencies I know do not teach it. I think it would be a bit presumptuous to assume that a brand new diver should have learned it in their basic instruction.
fire_diver
Contributor
well i know the basics to dive ... but i dont think many OW divers know much about what i asked ... even the padi elearning doesnt say much about what i asked , keeping in mind that i still havent done dives with a dive computer or dive table i think i did it just fine !
it was just the OW course so you basically rely a lot on the instructor the first times
So you have zero concept of what your NDLs are, no PDC and just dive until you run low on air then come up? PLEASE, PLEASE read the links provided. If you don't understand them, find someone to help you learn because it is essential information. Please also spend some time looking online for how to plan a dive, how to use dive tables, and download a set of air diving tables.
Just randomly swimming around underwater is going to get you or a buddy hurt.
TN-Steve
Contributor
Check out this article.. Gas Management for Rec. Divers If you go down to the bottom, they have a very good "rule of thumb" formula. For a 80CF 3000 PSI tank, your "Rock Bottom" pressure (Air to get you and your buddy safely to surface with stop) is (depth (in feet) X 10) + 300. This is assuming a high consumption rate for the both of you, probably realistic for most divers (I suspect it would be for me) It varies a bit for other tanks. So, if you're at 60 feet, the ROCK BOTTOM is 900 PSI. That would get you and your buddy safe to the surface. You don't have to END your dive then, if you're on reef or any other situation where there are levels, you can just move up to shallower depth for a while.
This one article made it the most understandable for me, and I like the quick rule-of-thumb method he gives, it's easy, I can remember it, and do it in my head. FWIW, at 100 feet with an 80 AL tank, your rock bottom would be 1300 PSI.
This one article made it the most understandable for me, and I like the quick rule-of-thumb method he gives, it's easy, I can remember it, and do it in my head. FWIW, at 100 feet with an 80 AL tank, your rock bottom would be 1300 PSI.
well i know the basics to dive ... but i dont think many OW divers know much about what i asked ... even the padi elearning doesnt say much about what i asked , keeping in mind that i still havent done dives with a dive computer or dive table i think i did it just fine !
it was just the OW course so you basically rely a lot on the instructor the first times
---------- Post added August 21st, 2014 at 07:37 PM ----------
yeah , i get it now
fire_diver
Contributor
I don't find it presumptuous that someone doesn't know what they aren't taught, but I still find it sad how low the dive curriculum is and how few instructors teach beyond that bare minimum. Teaching rock-bottom isn't rocket-surgery, but new divers should come out with at least the concepts of tank volume to pressure relationship and what their SAC is for different activities.
I feel very strongly that a proper ascent strategy should be taught in OW. Rock bottom and min deco are concepts that a diver should know. There are agencies that teach these, I wish more did.
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30ft/second was changed to minute. I was looking at .5ft/second and thinking 30ft/minute.
Re. sac, if you look down in the rest of the post there is mention of multiply sac by at least 1.5 if not double.
To Boulderjohn, that's bs about them not supposed to have been taught about why they have to return with 500psi, what SAC rates are, and how to calculate bottom times. It may not be in the PADI curriculum, but it is paramount to diver safety and is taught by many other agencies in their basic classes. It may not be tested on, but it is in the books.
To the OP, what you will find is that many of us have great disdain for the majority of scuba instructors out there who unfortunately know very little about the theory of how and why certain things are taught. While much of this comes out as harsh, it is only meant to help you become a safer diver so you and/or your buddy are able to tell us about interesting things that have happened instead of us having to read about it.
fire_diver
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Yes, I was shocked the first time I had to ascend on a line instead of up a slope. 30ft/min (10 meters for our OP) equals counting "one thousand one" while moving up 6 inches (or roughly the length of my hand) which is much slower than rising with your "slowest bubbles". This feels incredibly slow until you get used to it.
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