What defines a "Deco" dive?
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You are absolutely correct and I will be more careful in future. Updated my original post.
Nicole, I think we've said everything there is to say about the incident . . . now the discussion is enjoying a segue, as conversations do -- and minimum deco is far less likely, I think, to get the thread derailed!
Bill, if you think about it, all dives involve decompression. GUE felt that a linear 60 or 30 fpm ascent to the surface or a shallow safety stop, especially from deeper recreational dives, was a "bend and mend" approach to the offgassing that everybody has to do. Their idea was to build ascents, from the very beginning of diving, that have the shape of ascents generated by deco software. That is a relatively rapid ascent when deep, slowing as one approaches the surface (that shape being dictated by the assumed exponential nature of gas kinetics). In keeping with the principle of beginning as one means to go on, GUE students are taught to do stepped ascents from the outset. This not only is likely to be a more conservative and useful ascent strategy, it also builds the skills needed for efficient and accurate profiles if one goes on to more advanced diving.
There is no research of which I am aware, to support this approach. (And don't bring up Marroni, because his ascents were slow all the way from the bottom, and not comparable.) However, I know quite a few people, including myself, who noted a decrease in post-dive fatigue when they adopted the minimum deco procedure. And yes, we do a stop on the way up from a 30 foot dive -- but it's at half maximal depth, so in practice, it's your 15 foot safety stop! And the ascent from 15 feet to the surface is far slower than typical; we try to take two minutes to do that, if conditions permit. It's good for you, and it's good practice!
Bill, if you think about it, all dives involve decompression. GUE felt that a linear 60 or 30 fpm ascent to the surface or a shallow safety stop, especially from deeper recreational dives, was a "bend and mend" approach to the offgassing that everybody has to do. Their idea was to build ascents, from the very beginning of diving, that have the shape of ascents generated by deco software. That is a relatively rapid ascent when deep, slowing as one approaches the surface (that shape being dictated by the assumed exponential nature of gas kinetics). In keeping with the principle of beginning as one means to go on, GUE students are taught to do stepped ascents from the outset. This not only is likely to be a more conservative and useful ascent strategy, it also builds the skills needed for efficient and accurate profiles if one goes on to more advanced diving.
There is no research of which I am aware, to support this approach. (And don't bring up Marroni, because his ascents were slow all the way from the bottom, and not comparable.) However, I know quite a few people, including myself, who noted a decrease in post-dive fatigue when they adopted the minimum deco procedure. And yes, we do a stop on the way up from a 30 foot dive -- but it's at half maximal depth, so in practice, it's your 15 foot safety stop! And the ascent from 15 feet to the surface is far slower than typical; we try to take two minutes to do that, if conditions permit. It's good for you, and it's good practice!
AbyssalPlains
Contributor
GUE asserts that there is no such thing as a no-deco dive, only minimum-deco dives. Minimum deco sort of boils down to an ascent strategy (0:01 stops every 10' from half depth), but without the sugar-coated name. The total ascent time under GUE MDL is not terribly different to a properly executed ascent + safety stop with PADI, NAUI, etc.
Blackwood
Contributor
It's analogous to "NDL dive."
An MDL ("minimum deco limit") is the time limit at (average bottom) depth for which the following generic ascent strategy applies: 30fpm to 1/2 depth, 10fpm up from there (usually 30 second stops and 30 second moves at each 10 foot increment).
GUE (and UTD) consider that to be the minimum amount of in water deco for any given dive, hence minimum deco. Beyond MDL, additional stops are required.
For PADI, minimum deco is max depth divided by 60fpm (i.e. 1 minute for a 60 foot dive). However they don't use the term. They use "no deco" limit, and bury the deco requirement in the ascent rate associated with the model.
Yes, and in fairness I'd probably need three hands to count the number of times I heard the phrase "all dives are deco dives" in my (PADI) open water course.
Discussing the same thing over at divematrix.com. What I find interesting is
1. Min deco is based on ZHL16C using GF's 30-85/30-90 which are not that conservative. I dive gradient factors of 30-75 (based on a recent bubble study and diver feedback)
2. Using a standard ZHL16C calculator, its a deco dive with stops starting at 40'.
3. Slowing the ascent during off gassing (10'/Min) is swapping hard stops for slow off gassing ascent.
4. Min Deco is a Deco dive.
5. With the gradient factors I use, I would incur closer to double the time in the water decompressing (whether slow ascent or hard stops). I certainly would not use a Mindeco profile - Too aggressive for me.
GUE specialists - What's the relevance of target depth and when is it appropriate to change the it/the plan?
Blackwood
Contributor
At the risk of getting more "off topic" posts deleted... 
What's the profile? 90 feet for 40 minutes on EAN32? Personally, I'd consider it an MDL dive (I use 40 as the limit for 90 feet on EAN32), and do about 6 minutes of in water deco (2 minutes to 40 and 4 minutes to surface). (Note that the NAUI table calls 40 feet NDL for 90 feet as well).
That said, I'm a big proponent of using what works for you. Thus far, this system works for me. It works for 1-4 dives a day, and it works for 30 dives over the period of a week (in either case with modifications for repet dives). For me.
12 minutes?
Pretty simple. Target depth is what you expect, plan and equip for. It's appropriate to change it when you find that expectation was wrong
What's the profile? 90 feet for 40 minutes on EAN32? Personally, I'd consider it an MDL dive (I use 40 as the limit for 90 feet on EAN32), and do about 6 minutes of in water deco (2 minutes to 40 and 4 minutes to surface). (Note that the NAUI table calls 40 feet NDL for 90 feet as well).
That said, I'm a big proponent of using what works for you. Thus far, this system works for me. It works for 1-4 dives a day, and it works for 30 dives over the period of a week (in either case with modifications for repet dives). For me.
12 minutes?
Pretty simple. Target depth is what you expect, plan and equip for. It's appropriate to change it when you find that expectation was wrong
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