I never realized that table can be used to plan a multi-level dive!
What a waste of money on learning how to use the "wheel" all those yrs ago. No wonder it is obsoleted nowadays.
diving with two algorithms
- Thread starter Remy B.
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What a waste of money on learning how to use the "wheel" all those yrs ago. No wonder it is obsoleted nowadays.
Basking Ridge Diver
Contributor
It is a very conservative approach - but if you understand the tables for a single square profile you can use it for a multi-level dive. So learning the old school method allows you to 1) understand what your computer is doing (if it gives a really skewed value you should be able to pick up on it) and 2) gives you a back up until you get another PDC.
I dive with one and if I had extra money maybe I would dive with 2 PDCs. But right now that is not in the budget - so I use what I have.
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Frontpointer1000
Contributor
The OP mentioned something that I find fascinating: he was diving two computers, one (the Suunto) apparently was set to nitrox (some unknown mixture, as he had to reprogram the EAN to 21% on his second dive to replicate air settings). It was the Suunto that gave him longer NDLs. Certainly it is possible that the difference in the computers was that the Suunto was considering nitrogen loading that had occurred from the first dive earlier that day (and which the Suunto computer had been programmed to consider the diver was diving on nitrox)--thus the diver would theoretically have less nitrogen loading and therefore longer NDLs on subsequent dives.
Now I'm relatively new to diving (in fact this is my first post here) so I could be off here, but this is what I am thinking:
Both the Mares Puck and the Suunto D4i use the RGBM algorithm. This is Bruce Weinke's mathematical model used to represent how tissue on-gasses and off-gasses at varying levels of compression (read: depth). Algorithms are complex mathematical models used to attempt to replicate the sophisticated minutae of complex human physiology under pressure, for decompression, and how gasses interact with tissue and various compartments in the human body. With this in mind, ANY diving is decompression diving, because our bodies undergo compression and at some point, decompression (hopefully!).
The trick is, these are mathematical approximations of a physiologically complex metabolic affair--they are not exact.y
From what I understand, the Mares RGBM (Reduced Gradient Bubble Model) becomes progressively more conservative with each repetitive dive which further makes sense regarding the OPs experience. The SUUNTO also uses the RGBM algorithm, though I think it is even more proprietary, as they call it the SUUNTO RGBM- and I tend to think they have tweaked it quite a bit over the years that they have been working with Dr. Weinke (SUUNTO states they have three RGBM algorithms they now employ). Someone with industry knowledge please chime in here.
When diving on a computer, I personally think we should understand the fundamental tenets of the algorithm our computer employs. After all, we are making decisions based on that algorithm.
The basic assumptions of the RGBM are the following:
1. Gas diffusion across a membrane is limited by perfusion (blood flow)
2. There is an ever present collection of gas bubbles of differing sizes
3. These bubbles can variably penetrate membranes at all pressures
4. Haldane tissue compartment theory applies, and these compartment half lives range in time from 1 -720 minutes.
To better understand this algorithm, it helps to understand two principles:
Half life: (at least in this context) is the time required to rid a particular compartment of half the load of nitrogen at any given time.
Gas diffusion: the assumption that inert gases enter and exit human body compartments of differing tissue as the ambient pressure changes. These gases do so at different rates based on the compartment and the pressure.
These principles are (from my limited understanding) based on original research by Haldane. Thus these theoretical compartments are called "Haldane Compartments". He was one cool scientist. He did research on himself, exposing himself to poisonous gases to measure their effect. He invented the first gas mask and was the first to use canaries in mines to ensure adequate oxygen levels for the miners. And he had a cool mustache.
So I use two computers when diving. One is the Suunto Cobra, one is the Aeris (now Oceanic) A300CS. The Suunto employs the RGBM algorithm, whereas the Aeris has a dual algorithm setting, so I can select which algorithm I want to dive off. On a recent dive trip I was diving Nitrox (my first trip to use nitrox). The Aeris had my nitrox settings, and the Suunto was set to air. I did this to see the difference in NDLs and other diving parameters the nitrox would offer. Remember, this was my first trip using using nitrox. I was diving off the southern tip of Fiji near an island called Beqa. It was toward the end of the trip and I'd done about 15 dives that week, usually on nitrox. On this particular dive, it was #2 of four planned that day. My previous dive was well within the limits. Pleasant SI, then we went for our second dive. Within one minute, at about 12 feet, my Aeris alarmed and called me for an 8 hr deco stop. Knowing this was an error, I dove my suunto. By the end of the dive, the aeris called for a 12 hr deco stop. I was always within table limits. The aeris is going back to the manufacturer for a checkup. I'm glad I was diving two computers that trip.
Now I'm relatively new to diving (in fact this is my first post here) so I could be off here, but this is what I am thinking:
Both the Mares Puck and the Suunto D4i use the RGBM algorithm. This is Bruce Weinke's mathematical model used to represent how tissue on-gasses and off-gasses at varying levels of compression (read: depth). Algorithms are complex mathematical models used to attempt to replicate the sophisticated minutae of complex human physiology under pressure, for decompression, and how gasses interact with tissue and various compartments in the human body. With this in mind, ANY diving is decompression diving, because our bodies undergo compression and at some point, decompression (hopefully!).
The trick is, these are mathematical approximations of a physiologically complex metabolic affair--they are not exact.y
From what I understand, the Mares RGBM (Reduced Gradient Bubble Model) becomes progressively more conservative with each repetitive dive which further makes sense regarding the OPs experience. The SUUNTO also uses the RGBM algorithm, though I think it is even more proprietary, as they call it the SUUNTO RGBM- and I tend to think they have tweaked it quite a bit over the years that they have been working with Dr. Weinke (SUUNTO states they have three RGBM algorithms they now employ). Someone with industry knowledge please chime in here.
When diving on a computer, I personally think we should understand the fundamental tenets of the algorithm our computer employs. After all, we are making decisions based on that algorithm.
The basic assumptions of the RGBM are the following:
1. Gas diffusion across a membrane is limited by perfusion (blood flow)
2. There is an ever present collection of gas bubbles of differing sizes
3. These bubbles can variably penetrate membranes at all pressures
4. Haldane tissue compartment theory applies, and these compartment half lives range in time from 1 -720 minutes.
To better understand this algorithm, it helps to understand two principles:
Half life: (at least in this context) is the time required to rid a particular compartment of half the load of nitrogen at any given time.
Gas diffusion: the assumption that inert gases enter and exit human body compartments of differing tissue as the ambient pressure changes. These gases do so at different rates based on the compartment and the pressure.
These principles are (from my limited understanding) based on original research by Haldane. Thus these theoretical compartments are called "Haldane Compartments". He was one cool scientist. He did research on himself, exposing himself to poisonous gases to measure their effect. He invented the first gas mask and was the first to use canaries in mines to ensure adequate oxygen levels for the miners. And he had a cool mustache.
So I use two computers when diving. One is the Suunto Cobra, one is the Aeris (now Oceanic) A300CS. The Suunto employs the RGBM algorithm, whereas the Aeris has a dual algorithm setting, so I can select which algorithm I want to dive off. On a recent dive trip I was diving Nitrox (my first trip to use nitrox). The Aeris had my nitrox settings, and the Suunto was set to air. I did this to see the difference in NDLs and other diving parameters the nitrox would offer. Remember, this was my first trip using using nitrox. I was diving off the southern tip of Fiji near an island called Beqa. It was toward the end of the trip and I'd done about 15 dives that week, usually on nitrox. On this particular dive, it was #2 of four planned that day. My previous dive was well within the limits. Pleasant SI, then we went for our second dive. Within one minute, at about 12 feet, my Aeris alarmed and called me for an 8 hr deco stop. Knowing this was an error, I dove my suunto. By the end of the dive, the aeris called for a 12 hr deco stop. I was always within table limits. The aeris is going back to the manufacturer for a checkup. I'm glad I was diving two computers that trip.
pdhenry
Contributor
I understand the theory but I don't understand why you're giving yourself a 10 minute surface interval when you're experiencing 0 minutes, and even with that I don't get the same outcome you're getting.
Using your 10 minute SI and the RDP I end up at PG "R" at the end of the day.
Using zero SI
90 ft @ 10 mins = PG "D"
D @ 70 ft: RNT = 13 mins
70 ft: 15 min ABT + 13 min RNT = 28 min TBT --> PG "N"
N @ 50 ft: RNT = 44 min
50 ft: 20 min ABT + 44 min RNT = 64 min TBT --> PG "U"
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This is just a reminder that it may make sense to use the tables the way either one of you are suggesting, and some people do it, but it is not designed to be used that way, and it has never been tested that way. The tables assume that when you begin your ascent, you will continue to the surface at a specified rate of ascent, during which time you will be off-gassing. It is very possible for you to make such an ascent and be in such a position that you can immediately descend and start another dive. In fact, the knowledge reviews for the table version of the course include a question in which the minimum surface interval between two dives is zero. It may well be possible to create a valid profile this way, but it has never been tested, and there is no official way to do it.
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Basking Ridge Diver
Contributor
To Boulderjohns point above - be careful if you are not comfortable with tables, keep practicing until you get comfortable - but this is how it works.
Using a NAUI table - NAUI Dive Tables - scroll down till you hit the larger tables (not the first one you can not read it...)
In the first table - first Dive to 90 feet for 10 mins - find 90 feet go to the 10 min mark and down that column is C.
In the second table go to the bottom of column C
10-1:39) - you can not go lower than 10 min SIT time with Naui - so look left on the second table your New Group is now C.In the third table - using the New Group of C go left till you hit 70 feet (RNT is 15 and AMDT is 30).
Again in the first table - second Dive (same dive because of the 10 min SIT per NAUI) go to 70 feet for 30 mins (15 RNT + 15 min second dive) and down that column is F.
Again in the second table - go to the bottom of column F
10-:45) - you can not go lower than 10 min SIT time with NAUI - so look left on the second table your New Group is F.Again in the third table - using the New Group of F go left until you hit 50 feet (RNT is 47 and AMDT is 33).
Again in the first table - third Dive (same dive because of the 10 min SIT per NAUI) go to 50 feet for 67 mins (47 RNT + 20 min third dive - there is not a 67 you have to go to 70 mins) and down that column is I.
Again in the second table - go to the bottom of column I
10-:33) - you can not go lower than 10 min SIT time with NAUI - so look left on the second table your New Group is I.Again in the third table - the only possible dive is in 40 or 50 feet all others you can not do... But now you will be pushing the NDLs - my recommendation is to ascend do a safety stop and do a long SIT to recover from your dive.
Does this help?
pdhenry
Contributor
Isn't "the Wheel" just a different presentation of the RDP, designed to facilitate multi-level diving? I haven't used a Wheel but that's my understanding.
Here's an analysis on using the RDP tables to plan multi-level dives with conservatism equal to or greater than the Wheel. It presents lower time limits/loading for the subsequent depths in the multidepth profile.
It's a little academic for me, since I wouldn't care to dive routinely without a computer tracking time & depth.
Here's an analysis on using the RDP tables to plan multi-level dives with conservatism equal to or greater than the Wheel. It presents lower time limits/loading for the subsequent depths in the multidepth profile.
It's a little academic for me, since I wouldn't care to dive routinely without a computer tracking time & depth.
Basking Ridge Diver
Contributor
Sorry I also realized you are using PADI and I was using NAUI - so yes you would have used 0 SIT time in your example.
My only point originally is I have a computer and I carry a table with me. I am not advocating tables if your PDC is working but if it does die on you - you can use a table to continue to dive - but you must be vigilant in using tables because there is nothing that will beep or light up if you go over your times....
It is just you, a table, a timer, a depth gauge and a couple notes on a slate if you use a slate... Be careful but this can be used to dive...
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