Imported post
This is a follow on from the guy who wrote the article on dive 'pooters. I'll do it in three parts;
Understanding the shape of the curve; a technique for demystifying decompression
In an earlier article, I presented reasons why dive computers simply aren't the best option for general use in technical diving. It seems appropriate to follow it up with an article pointing out my idea of a better option.
First of all, we should put things into some kind of perspective. This article is not a how-to guide to decompression diving without a computer. The topic of staged decompression diving is complex and can't possible be covered adequately in a short article such as this. In any event, staged decompression diving is a very dangerous sport and my sincere advice is don't take part in it at all.
Secondly, the real intention of this article is to outline a technique I have taught to interested and qualified divers for several years. It's not a foolproof way of producing a decompression schedule, there is no foolproof way of doing that, but it has been used without incident in various locations, most particularly in the Great Lakes region of North America, where the water is cold and conditions tough. Bear in mind, what is being presented here is just an outline. There are a couple of steps I have purposely glossed over to disable the information. I say again: Don't try this you'll die.
Do you remember doing pre-calculus in high school? Functions, x-y coordinates, plotting, graph paper, sound familiar? No, most people are in the same boat, but no worries. There's no math here, just some simple addition and subtraction that doesn't even require a calculator.
Anyhow, if you did remember your math classes, you'd recall that it's possible to describe all sorts of complex calculations by drawing simple and elegant curves. The point being: There's a pattern somewhere out there among all those f (x, y)'s and tangents, and if you can just find it, you can solve all sorts of complicated problems very fast and impress people.
OK, so math wasn't a core competency in school. How about music? Playing the guitar for instance? And if you didn't play in the school band, perhaps you wore a Mohawk and played in a punk band! If you did, you'll know that most songs about sex, drugs and rock and roll require you to know only three chords as long as you play them real fast. The trick to playing fast is using one chord shape (the pattern formed by your fingers pressing down on the strings) and sliding it up and down the neck of the guitar; an E played at the top of the guitar's neck becomes an F one fret down, a G three down and an A if you move it down a couple more. Wow, that's four chords for the price of one! The point being: There's a pattern somewhere out there among all those B flats and C minors, and if you can just find it, you can play all sorts of neat sounding music very fast and impress people.
So what does this have to do with plotting a decompression schedule? Well, everything. You see the calculations made within a decompression algorithm ; any decompression algorithm can be expressed quite nicely as a pattern, just like one of those functions from high school. In fact, in most cases, we can find an anchor point for the algorithm where that pattern becomes a very simple gentle curve expressed against time and depth.
Broadly speaking, every gas mixture, every flavor of nitrox or trimix, has its own particular shape and anchor point, which can be learned and applied to any dive using that mix.
If we apply the guitar analogy, each gas mixture has its shape and it can be moved up and down in the water column to cover longer, shorter, deeper and shallower dives with that gas just like we can move a chord shape up and down the guitar neck to play different notes.
By adopting the practice of using standard mixes, we further simplify the learning process, effectively, be only have to learn a couple of chord shapes to cover just about every tune, or dive, we are going to do.
Now all this is fine, but where do we start? What shape is an E chord?
First, you have to pick an algorithm that makes you feel comfortable, safe and secure. There are plenty of them out there, so take your pick.
Once you have your algorithm, you have to think about which gas mixes you intend to use as your gold standard.
For my personal use, I've adopted the VPM-b algorithm as published by Ross Hemmingway from code developed by Erik C. Baker. What I like about this solution to the "deco challenge" is that both the mathematical premise and the physiological state it's designed to model, make sense to me. It's also got enough of a track record for me to feel comfortable with it. Hemmingway's version of it is inexpensive to buy, runs on most windows platforms, is simple to use, is relatively bug-free, and is supported and updated professionally and regularly by its creator. If you want to check it out, go to http://www.hhssoftware.com/v-planner/index.html.
Standard gases for deep dives include a mix containing about 16% oxygen, 45% helium with nitrogen making up the remainder. This is a dangerous mix to breathe until you get about 10 feet underwater, so we need to use a travel mix with it, my choice is another helium, oxygen and nitrogen mix with 32% oxygen and 25% helium. To round things out, we need something to accelerate decompression. The standard mixes would be a 50% nitrox and pure oxygen.
With this in mind, here's a schedule kicked out by V-Planner for a dive to 245 feet for 30 minutes; a modest dive by some standards, but an excellent place to start to build a "deco baseline". Look at it and see if you see any sort of pattern.
Dec to 120ft (2) on Trimix 32.0/25.0, 50ft/min descent.
Dec to 200ft (4) on Trimix 16.0/45.0, 50ft/min descent.
Dec to 245ft (4) on Trimix 16.0/45.0, 60ft/min descent.
Level 245ft 25:15 (30) on Trimix 16.0/45.0, 1.31 ppO2, 103ft EAD
Asc to 200ft (30) on Trimix 16.0/45.0, -50ft/min ascent.
Asc to 165ft (32) on Trimix 16.0/45.0, -30ft/min ascent.
Stop at 165ft 0:56 (33) on Trimix 16.0/45.0, 0.94 ppO2, 64ft EAD
Stop at 160ft 1:00 (34) on Trimix 16.0/45.0, 0.91 ppO2, 62ft EAD
Stop at 155ft 1:00 (35) on Trimix 16.0/45.0, 0.89 ppO2, 59ft EAD
Stop at 150ft 1:00 (36) on Trimix 16.0/45.0, 0.86 ppO2, 57ft EAD
Stop at 145ft 1:00 (37) on Trimix 16.0/45.0, 0.84 ppO2, 54ft EAD
Stop at 140ft 1:00 (38) on Trimix 16.0/45.0, 0.82 ppO2, 52ft EAD
Stop at 135ft 2:00 (40) on Trimix 32.0/25.0, 1.59 ppO2, 58ft EAD
Stop at 95ft 1:50 (43) on Trimix 32.0/25.0, 1.21 ppO2, 36ft EAD
Stop at 90ft 1:00 (44) on Trimix 32.0/25.0, 1.16 ppO2, 33ft EAD
Stop at 85ft 1:00 (45) on Trimix 32.0/25.0, 1.12 ppO2, 30ft EAD
Stop at 80ft 1:00 (46) on Trimix 32.0/25.0, 1.07 ppO2, 28ft EAD
Stop at 75ft 2:00 (48) on Nitrox 50.0, 1.60 ppO2, 35ft EAD
Stop at 65ft 1:50 (50) on Nitrox 50.0, 1.45 ppO2, 28ft EAD
Stop at 60ft 1:00 (51) on Nitrox 50.0, 1.38 ppO2, 25ft EAD
Stop at 55ft 2:00 (53) on Nitrox 50.0, 1.30 ppO2, 22ft EAD
Stop at 50ft 2:00 (55) on Nitrox 50.0, 1.23 ppO2, 19ft EAD
Stop at 45ft 2:00 (57) on Nitrox 50.0, 1.15 ppO2, 16ft EAD
Stop at 40ft 3:00 (60) on Nitrox 50.0, 1.08 ppO2, 12ft EAD
Stop at 35ft 4:00 (64) on Nitrox 50.0, 1.01 ppO2, 9ft EAD
Stop at 30ft 3:00 (67) on Nitrox 50.0, 0.93 ppO2, 6ft EAD
Stop at 25ft 5:00 (72) on Nitrox 50.0, 0.86 ppO2, 3ft EAD
Stop at 20ft 5:00 (77) on Oxygen, 1.57 ppO2, 0ft EAD
Stop at 15ft 23:00 (100) on Oxygen, 1.42 ppO2, 0ft EAD
Asc to sfc. 2:00 (102) on Oxygen, -10ft/min ascent.
Off gassing starts at 197.5 ft
This is a follow on from the guy who wrote the article on dive 'pooters. I'll do it in three parts;
Understanding the shape of the curve; a technique for demystifying decompression
In an earlier article, I presented reasons why dive computers simply aren't the best option for general use in technical diving. It seems appropriate to follow it up with an article pointing out my idea of a better option.
First of all, we should put things into some kind of perspective. This article is not a how-to guide to decompression diving without a computer. The topic of staged decompression diving is complex and can't possible be covered adequately in a short article such as this. In any event, staged decompression diving is a very dangerous sport and my sincere advice is don't take part in it at all.
Secondly, the real intention of this article is to outline a technique I have taught to interested and qualified divers for several years. It's not a foolproof way of producing a decompression schedule, there is no foolproof way of doing that, but it has been used without incident in various locations, most particularly in the Great Lakes region of North America, where the water is cold and conditions tough. Bear in mind, what is being presented here is just an outline. There are a couple of steps I have purposely glossed over to disable the information. I say again: Don't try this you'll die.
Do you remember doing pre-calculus in high school? Functions, x-y coordinates, plotting, graph paper, sound familiar? No, most people are in the same boat, but no worries. There's no math here, just some simple addition and subtraction that doesn't even require a calculator.
Anyhow, if you did remember your math classes, you'd recall that it's possible to describe all sorts of complex calculations by drawing simple and elegant curves. The point being: There's a pattern somewhere out there among all those f (x, y)'s and tangents, and if you can just find it, you can solve all sorts of complicated problems very fast and impress people.
OK, so math wasn't a core competency in school. How about music? Playing the guitar for instance? And if you didn't play in the school band, perhaps you wore a Mohawk and played in a punk band! If you did, you'll know that most songs about sex, drugs and rock and roll require you to know only three chords as long as you play them real fast. The trick to playing fast is using one chord shape (the pattern formed by your fingers pressing down on the strings) and sliding it up and down the neck of the guitar; an E played at the top of the guitar's neck becomes an F one fret down, a G three down and an A if you move it down a couple more. Wow, that's four chords for the price of one! The point being: There's a pattern somewhere out there among all those B flats and C minors, and if you can just find it, you can play all sorts of neat sounding music very fast and impress people.
So what does this have to do with plotting a decompression schedule? Well, everything. You see the calculations made within a decompression algorithm ; any decompression algorithm can be expressed quite nicely as a pattern, just like one of those functions from high school. In fact, in most cases, we can find an anchor point for the algorithm where that pattern becomes a very simple gentle curve expressed against time and depth.
Broadly speaking, every gas mixture, every flavor of nitrox or trimix, has its own particular shape and anchor point, which can be learned and applied to any dive using that mix.
If we apply the guitar analogy, each gas mixture has its shape and it can be moved up and down in the water column to cover longer, shorter, deeper and shallower dives with that gas just like we can move a chord shape up and down the guitar neck to play different notes.
By adopting the practice of using standard mixes, we further simplify the learning process, effectively, be only have to learn a couple of chord shapes to cover just about every tune, or dive, we are going to do.
Now all this is fine, but where do we start? What shape is an E chord?
First, you have to pick an algorithm that makes you feel comfortable, safe and secure. There are plenty of them out there, so take your pick.
Once you have your algorithm, you have to think about which gas mixes you intend to use as your gold standard.
For my personal use, I've adopted the VPM-b algorithm as published by Ross Hemmingway from code developed by Erik C. Baker. What I like about this solution to the "deco challenge" is that both the mathematical premise and the physiological state it's designed to model, make sense to me. It's also got enough of a track record for me to feel comfortable with it. Hemmingway's version of it is inexpensive to buy, runs on most windows platforms, is simple to use, is relatively bug-free, and is supported and updated professionally and regularly by its creator. If you want to check it out, go to http://www.hhssoftware.com/v-planner/index.html.
Standard gases for deep dives include a mix containing about 16% oxygen, 45% helium with nitrogen making up the remainder. This is a dangerous mix to breathe until you get about 10 feet underwater, so we need to use a travel mix with it, my choice is another helium, oxygen and nitrogen mix with 32% oxygen and 25% helium. To round things out, we need something to accelerate decompression. The standard mixes would be a 50% nitrox and pure oxygen.
With this in mind, here's a schedule kicked out by V-Planner for a dive to 245 feet for 30 minutes; a modest dive by some standards, but an excellent place to start to build a "deco baseline". Look at it and see if you see any sort of pattern.
Dec to 120ft (2) on Trimix 32.0/25.0, 50ft/min descent.
Dec to 200ft (4) on Trimix 16.0/45.0, 50ft/min descent.
Dec to 245ft (4) on Trimix 16.0/45.0, 60ft/min descent.
Level 245ft 25:15 (30) on Trimix 16.0/45.0, 1.31 ppO2, 103ft EAD
Asc to 200ft (30) on Trimix 16.0/45.0, -50ft/min ascent.
Asc to 165ft (32) on Trimix 16.0/45.0, -30ft/min ascent.
Stop at 165ft 0:56 (33) on Trimix 16.0/45.0, 0.94 ppO2, 64ft EAD
Stop at 160ft 1:00 (34) on Trimix 16.0/45.0, 0.91 ppO2, 62ft EAD
Stop at 155ft 1:00 (35) on Trimix 16.0/45.0, 0.89 ppO2, 59ft EAD
Stop at 150ft 1:00 (36) on Trimix 16.0/45.0, 0.86 ppO2, 57ft EAD
Stop at 145ft 1:00 (37) on Trimix 16.0/45.0, 0.84 ppO2, 54ft EAD
Stop at 140ft 1:00 (38) on Trimix 16.0/45.0, 0.82 ppO2, 52ft EAD
Stop at 135ft 2:00 (40) on Trimix 32.0/25.0, 1.59 ppO2, 58ft EAD
Stop at 95ft 1:50 (43) on Trimix 32.0/25.0, 1.21 ppO2, 36ft EAD
Stop at 90ft 1:00 (44) on Trimix 32.0/25.0, 1.16 ppO2, 33ft EAD
Stop at 85ft 1:00 (45) on Trimix 32.0/25.0, 1.12 ppO2, 30ft EAD
Stop at 80ft 1:00 (46) on Trimix 32.0/25.0, 1.07 ppO2, 28ft EAD
Stop at 75ft 2:00 (48) on Nitrox 50.0, 1.60 ppO2, 35ft EAD
Stop at 65ft 1:50 (50) on Nitrox 50.0, 1.45 ppO2, 28ft EAD
Stop at 60ft 1:00 (51) on Nitrox 50.0, 1.38 ppO2, 25ft EAD
Stop at 55ft 2:00 (53) on Nitrox 50.0, 1.30 ppO2, 22ft EAD
Stop at 50ft 2:00 (55) on Nitrox 50.0, 1.23 ppO2, 19ft EAD
Stop at 45ft 2:00 (57) on Nitrox 50.0, 1.15 ppO2, 16ft EAD
Stop at 40ft 3:00 (60) on Nitrox 50.0, 1.08 ppO2, 12ft EAD
Stop at 35ft 4:00 (64) on Nitrox 50.0, 1.01 ppO2, 9ft EAD
Stop at 30ft 3:00 (67) on Nitrox 50.0, 0.93 ppO2, 6ft EAD
Stop at 25ft 5:00 (72) on Nitrox 50.0, 0.86 ppO2, 3ft EAD
Stop at 20ft 5:00 (77) on Oxygen, 1.57 ppO2, 0ft EAD
Stop at 15ft 23:00 (100) on Oxygen, 1.42 ppO2, 0ft EAD
Asc to sfc. 2:00 (102) on Oxygen, -10ft/min ascent.
Off gassing starts at 197.5 ft
