WetLens,
Let me first emphasize that I'm not trying to dog you - I'm trying to explain an answer to your question regarding 'why you wound up with 43 minutes of deco obligation on your computer'. Not knowing what you know and what you don't know requires some assumptions to be made on my part, which may or may not be valid.
The bottom line is that while I am not familiar with your computer, I am very familiar with decompression software and I dive with Ross Hemingway's V-Planner - whose website I commend to your attention if you are interested in a deeper understanding of computer models:
V-Planner VPM & VPM-B & VPMB & VPM-B/E dive decompression software
Based on my familiarity with decompression software, I conclude that your computer may not have malfunctioned in giving you a deco time of 43 minutes under the circumstances you describe. It's just an opinion. Take it for what it's worth.
Doc: Thanks for taking the time to respond. I did not put this post in the deco thread as I was not looking to get into an in-depth discussion of decompression theory - I was trying to understand why my gage reacted the way it did - which I do not believe to be based in decompression theory.
WetLens, the reason why your computer reacted the way it did is in fact due to it's decompression algorithm - into which the computer loaded the specific variables that led it to calculate that 43 minutes of deco at 10'. The algorithm in your computer, in turn, is in fact based on decompression theory.
I am having trouble following your logic - primarily on the "missed" deco stop. I did not "miss" a deco stop - I cut it short, but that is much later in the dive. That is another topic altogether - one that may belong in the deco section. Let me see if I follow this logic... Ascend from 47' to 46' and stop for 4 minutes. The average depth of the dive to this point was 47'. The maximum depth of the dive was 59'. Why would I "stop" at 46'? This would simply add more time to my deco obligation.
Actually, no it might not. Decompression software such as V-Planner provides a "depth at which the diver begins to offgas". This depth is a variable that depends on total nitrogen loading over time and deepest depth - it identifies point along a curve (on ascent) where ambient pressure begins to allow gas to come out of solution and offgassing begins. Unless you worked the dive out in advance (or dived that profile routinely) you might not know when that point in your dive would be reached - but I suspect your computer was telling you that at 1:08, at a depth of 46', based on your total residual nitrogen loading, you needed to hold 46' for 4 minutes as a deco stop.
When you began your ascent at 1:10, about a minute and a half later, as shown on your computer's dive profile (your second attachment), you in effect omitted 4 minutes of decompression - or "missed a deco stop", or "cut short a stop" - that your computer was telling you needed to be made. It is not just a matter of semantics. You did not remain at 46' for 4 minutes to offgas. Consequently the computer compounded your deco obligation.
Looking at the matrix you attached, and watching the deco times as you ascended, this is the only explanation that makes sense with regard to why your times increased geometrically.
I
assume you have not gone into deco very often previously? Lets look at two quotes:
"Situation: 4th dive of the day and started the dive with 5 NIBR. 1:08 into the dive (avg depth 47') went into deco (current depth - 46'; deco obligation - 4 minutes). Notified my buddy of the need to ascend and began ascent at 1:10 (current depth - 44'; deco obligation - 24 minutes!). Hit roughly 10' at 1:13 well within ascent rate deco obligation 43 minutes!!!!!"
"At 1:08 the computer was telling me to go to 10' and spend 4 minutes. [In all honesty, I likely did not see the computer at this point - it was probably at the 1:09 mark, perhaps even 1:10, before I recognized the situation.]"
Again, while I'm not familiar with your specific computer, I suspect your computer was telling you to hold a 4 minute deco stop
at 46'. Had you done so, it is probable that you could have thereafter ascended without adding to your deco obligation.
Take another look at the second graphic you attached, which portrays your dive profile. Note that at 1:08 it goes into red - signifying that at that point you had a deco obligation. A deco curve does not look like your dive profile thereafter, which shows your ascent beginning directly afterward. A planned deco curve is smoother and does not have that sudden vertical ascent that your dive profile illustrates. I believe your computer was trying to tell you to hold 46' for 4 minutes in addition to whatever deco stops it showed you at 20' and 10' - because your computer calculated that you were in fact already offgassing N2 at 46'.
Again, I fail to see how I "missed" every stop between 45' and 10'. The computer was telling me to go to 10' - and I was, a bit slower than it wanted me to. My ascent rate was about 10 feet per minute due to following the slope of the bottom. When we hit the area of the boat, my direct ascent to the 10' stop was in the 26-30 feet per minute range. I understand that ascent rate is part of the decompression process. As it was slower than the theoretical 30' per minute, it was rightfully counting my ascent time as a continuation of the dive. I can accept that. What I can't accept is the rate at which it added the required 10' decompression stop time. This is where I cannot find logic.
Typically, though perhaps not in every case, deco profiles are calculated in 10' intervals during the ascent. I suspect - as noted above - that your computer was
not telling you to ascend directly to 10'. It was telling you to hold 46' for 4 minutes. When you did not do that, had you been watching it during the ascent, it would have told you to hold some other depth for some other time (during your ascent). The Wisdom would have calculated stops for 40', 30', and 20' - although I don't know if it was displaying any of these because your ascent rate would have required it to recalculate constantly. Because you did not see any recalculations or hold any deco stops at all during the ascent, and in fact you state:
"I skipped the "safety stop" at 20' and went directly to 10' just what the computer said to do."
I suspect that you possibly didn't understand that it wanted you to hold a deco stop at 46', and you failed to stop at 20', so you didn't hold what it would have given you as a deco stop at the 20' level, thus it piled all that omitted deco on you at the 10' stop - which is how you wound up with a 43 minute deco obligation at 10'. This is, based on my deco planning experience, the only explanation that makes sense. (But hell, I could be completely mistaken!
)
I've reviewed the matrix you provided as attachment 1. I see your point in terms of the matrix displaying a 10' stop. (I'm not certain what your wrist display showed, but clearly the matrix has a default setting for 10' stops.) The explanation is inadequate based on that matrix alone, however, the explanation I've provided above (along with a22shady) is consistent with the behavior of decompression software that I'm familiar with, VPM-B parameters, and omitted decompression consequences.
I suggest you try working out some deco profiles with the downloadable dive software from Sherwood, and/or contact Sherwood for a more in-depth review of which algorithm they are using.
Anyway, best with it in the future, and I hope this clarifies what I was trying to explain regarding how you could logically have gone from 4 minutes of deco at 46' to 43 minutes of deco at 10'.
Doc
