Unrealistic Deco Time

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

Thanks for the response as I am still learning! I truly appreciate reading the insightful posts.

I just started reading Deco For Divers (fantastic book suggested by a member here at SB) and was reminded of this thread.
 
craracer, by definition, he exceeded an M-value. By surfacing when his computer still showed a deco obligation, he went to a shallower depth than his algorithm felt was safe -- that's exceeding an M-value. Whether the M-value he exceeded is "accurate" in terms of predicting a certain likelihood of a bad outcome is another question.
 
I love this! Every time I start to think that I'm getting good at something.....

Humble pie never tasted so good.:D

Sorry for the hijack, but nonetheless, thanks to everyone.
 
Hijack was very welcome - you hijacked it back to topic, which is great. :)

+1 on what TSandM said. :) Nicely put!

What I was trying to say earlier is that the exact M value should be overshadowed by a more practical thought:

A solution to the problem would have been a shorter dive time, a better choice in breathing gas, a longer surface interval, or any combination thereof.

Of less importance is the actual M value or the accuracy of the calculations within his computer.

Clearly, he's mentioned that he knows this already - I'm not repeating it because I want to "beat him up," but because in the aftermath of the dive, his focus is on the accuracy of his computer, which isn't the point that should be learned.

The lesson is, "Less," not, "Computer bad."

Anyone that wants to hook up this weekend for that dive or burger & beer can call me at 843-252-4500. I'm buying... :)
 
It's not private code... we go into a shop at a remote dive site and ask for a 210 mix... "Air, please."...
Really? You (and whoever "we" constitutes) are the only person in the world I've ever heard use the term "210 mix" for air. 'Course I've only been around the diving community since 1961, and I may not have been paying all that much attention.
It may not be "private code" but it's definitely a foreign language.
By the way, air is a very poor choice for "210 mix."
:)
Rick
 
A few things in this thread don't make sense to me:
  • it suggested that the reason the OP's deco time ramped up rapidly was because he broke his ceilings. I can't believe that is correct. Firstly, he had only just tipped in deco, so his ceiling is going to be 10', not anything deeper (although I accept that he might have violated ascent rates). I think IanR33 made this point.
  • if he had violated his ascent ceiling, his computer would have told him to descend below the ceiling, not ramped up his time at the 10' stop.
  • it is also suggested at various points that his computer was too conservative. Sherwoods actually use one of the most aggressive algorithms (if not the most aggressive algorithm) on the recreational market.
 
:popcorn: Thanks, everyone. I've enjoyed this discussion.

Please keep in mind that the original intent of this thread was to get Sherwood's input on the subject. They have yet to weigh in. Again, thanks for everyone else's input.

Everyone can start throwing darts, but I remain unconvinced that I truly missed 30 minutes of deco. I am anxiously awaiting DiveNav's analysis, but every simulation that I have run indicates that I served my time before surfacing. I understand everyone's points concerning reliance on the tool you have in-hand and issues with getting sufficient accuracy in a simulation. Others suggested that I plan the dive in V-Planner and use the gage as back-up. Results for the 4th dive of the day would have been less time at 10' before surfacing - not 30 minutes more. Again, I respect everyone's points and I understand that the real issue is adjusting my behavior to avoid deco. Message heard and agreed.

It is very unusual that I dive with just the Wisdom. I have Orca Pilots (Nitrox version) that I use as backups. As far as the Wisdom being less conservative than other computers, I'd have to say the Orca is even less conservative when in the normal (0) mode. The Orca has the capability of adding conservative factors; I have not found a similar feature on the Wisdom. My typical method of diving the Orca was to maintain 2 digits of dive time remaining. If I got to 1 digit, I ascended - typically a major step - in the range of 20' if possible. That practice was a carry-over from the Edge days of staying 2 pixels above the line (which was partly a carry-over from multi-level dive planning with tables).

That practice does not work effectively with the Wisdom as it incorporates air consumption into the mix. My dives are typically governed by air consumption, not deco. I find this an annoying aspect of diving with the Wisdom and may be a contributing factor in getting lax. I am likely to go back to a computer that monitors deco status only.

I still believe there is something amiss in the way the computer "piles" on time at 10'. Let me emphasize that I am not using this as an excuse for my poor behavior. No matter what gage I use, I have to use the data provided to guide the dive. That means I have to be looking at the gage! Again, points taken, understood, agreed.

BTW, Sherwood, if you are listening: I dug through both my wife's and my data and have found a couple more examples very similar to what happened on this dive. One from last Friday night. First dive, square profile. Very similar exponential increase in 10' stop time. The dive was well within safe no-deco limits as the computer reset itself to air. My wife was diving the Orca (set properly) with the Wisdom (set to air) as backup. Did not even see it until I researched historical data.
 
Sherwood Scuba is very concerned about the question posed here. We are very glad that nobody was injured. Based on what we have seen, it does not appear the computer malfunctioned. We have sent wetlens a private message to get more specific information to resolve this question. This thread has proven a few points. Many divers dive many different ways with many different types of equipment and we all have our own opinions. No one piece of equipment will work for us all and we all must determine the type of diving we will be doing and the best equipment for that type of diving. Diving safe in whatever environment we are in is the most important aspect. Learning more about how your equipment works is part of the safety aspect. We will get wetlens answers and post the outcome so we can all learn from this. In the meantime, read your computer manuals, utilize any simulators, take any classes, pay attention to warnings/alarms, review your dive plan before entering the water on mulitple dives, know what to do if the limits are exceeded and just be safe out there.
Safe diving,
Sherwood Scuba
 
I use a Wisdom 2 (the one without a preset deep stop, although I always do one anyway), and only once have I gone into Deco mode with it; it was my second dive one Saturday morning in Jupiter, so we're talking 45 mins at 70' for the first, and going on 44 mins. at about the same depth for the second when I noticed the obligation, both using a 32% mix.

Once I noticed the Wisdom was in Deco (from me not paying attention, of course), I also noticed that it said to ascend to 10' for three minutes of deco time. I thought, "10' can't be right" and seeing as I still had plenty of gas, I decided to just ascend at a normal rate to 35' for my usual 3-minute deep stop. By the time I finished that, the deco obligation was still reading 10' but only two minutes. I then ascended normally to safety stop and then up, but by the time I reached 20' (which triggers the safety stop timer on the Wisdom), the deco obligation was already gone, so I did my safety stop and ascended without further incident or weirdness from the Wisdom. Total dive time for that second dive ended up being 54 minutes.

So, my bad for not paying attention and going into deco, but I certainly did not experience any wild increase in obligation times, and in fact the obligation cleared upon a normal ascent. However, this was only the second of two dives, not nearly as aggressive as the multiple dives you had done, WetLens.

I still think the computer was being silly telling me to ascend to 10' from my 70' depth, but this is a rec computer so I don't give its deco abilities much creedence anyway. I wasn't going to surface without making it happy and clearing the obligation, but I wasn't going to head straight to 10' like it wanted me to, either.

Mostly what it taught me was to pay closer attention to my computer, don't push the limits, and don't go into deco. I've done over 100 dives with it since and never crossed that line again. I'm a rec diver and deco is for techies - I can't imagine actually PLANNING to hang around on a line at various depths just breathing gas.

So, I am also interested in hearing Sherwood's take on this incident.
 
Really? You (and whoever "we" constitutes) are the only person in the world...

"We" are my 11 employees and myself. We are professional divers - light commercial work.

...I've ever heard use the term "210 mix" for air.

It was a joke, Rick.

For what it's worth, we don't actually request the stuff... The times where we are on a remote site, we're often asked why there's a 210 sticker on the tank. The truth is, we label all of our bottles with a MOD - it's a simple, straightforward method of labeling and telling the diver how deep he can go using that gas, based on PO2s. Typically, the labels will say, "20," "70," "100," "120," or "210." Sometimes we use other gasses for deeper dives that include helium, which will be labeled another number... But most of our work is typically pretty shallow and the above covers it most of the time.

...But I was joking about it. I don't know why you're still focusing on the subject. Get over it.

'Course I've only been around the diving community since 1961, and I may not have been paying all that much attention.

Wow, good on ya, pops. Did you teach Jacques Cousteau how to dive? :)

Jeez, Rick, lighten up.

I suppose that I'm a youngster, having only done this since 1986... Twenty-four years.

'Course, since you're stacking up and trying to show off, I suppose it's only fair to tell you that I've been doing this 60 hours a week for the past six years... Diving, that is, not talking about it. My bet is that my past six years' experience alone may compare favorably to most peoples' lifetime of diving... But I don't think it really matters.

Why do you?

Everyone can start throwing darts, but I remain unconvinced that I truly missed 30 minutes of deco.

Well, it depends on how you look at it.

According to some algorithms, I'm sure you're correct - but you were using the Wisdom, which said that you DID miss 30 minutes of decompression.

Well, that is, until you did a fifth dive and did your in-water recom... er, "delayed decompression." :D

Again, I respect everyone's points and I understand that the real issue is adjusting my behavior to avoid deco. Message heard and agreed.

Cool. Sounds like you learned something. I know I did when I made the same mistake.

It is very unusual that I dive with just the Wisdom. I have Orca Pilots (Nitrox version) that I use as backups. As far as the Wisdom being less conservative than other computers, I'd have to say the Orca is even less conservative when in the normal (0) mode. The Orca has the capability of adding conservative factors; I have not found a similar feature on the Wisdom. My typical method of diving the Orca was to maintain 2 digits of dive time remaining. If I got to 1 digit, I ascended - typically a major step - in the range of 20' if possible. That practice was a carry-over from the Edge days of staying 2 pixels above the line (which was partly a carry-over from multi-level dive planning with tables).

That practice does not work effectively with the Wisdom as it incorporates air consumption into the mix. My dives are typically governed by air consumption, not deco. I find this an annoying aspect of diving with the Wisdom and may be a contributing factor in getting lax. I am likely to go back to a computer that monitors deco status only.

With all due respect, isn't that a complicated solution? Isn't there a simpler solution that would be - forgive me for saying it - easier to stick to?

Sherwood Scuba is very concerned about the question posed here. We are very glad that nobody was injured. Based on what we have seen, it does not appear the computer malfunctioned. We have sent wetlens a private message to get more specific information to resolve this question. This thread has proven a few points. Many divers dive many different ways with many different types of equipment and we all have our own opinions. No one piece of equipment will work for us all and we all must determine the type of diving we will be doing and the best equipment for that type of diving. Diving safe in whatever environment we are in is the most important aspect. Learning more about how your equipment works is part of the safety aspect. We will get wetlens answers and post the outcome so we can all learn from this. In the meantime, read your computer manuals, utilize any simulators, take any classes, pay attention to warnings/alarms, review your dive plan before entering the water on mulitple dives, know what to do if the limits are exceeded and just be safe out there.
Safe diving,
Sherwood Scuba

Thanks for your input, Sherwood... Great to see you on here, and we look forward to your insight.

Mostly what it taught me was to pay closer attention to my computer, don't push the limits, and don't go into deco.

Nicely put! Sounds like you learned the lesson well, too. :)

I've done over 100 dives with it since and never crossed that line again. I'm a rec diver and deco is for techies - I can't imagine actually PLANNING to hang around on a line at various depths just breathing gas.

Lol... It's not my favorite thing to do either... But ya gotta go where the money is... :)

So, I am also interested in hearing Sherwood's take on this incident.

Ditto. :)
 
https://www.shearwater.com/products/perdix-ai/

Back
Top Bottom