As a rec diver, what to do if I breach my computer's NDL???

[waterpirate]

The problem with occupying " that space between " is the inherant risk you assume repeatedly. God forbid, but when you or someone you know goes tits up for what ever reason, and possibly has to get met at the dock by the helicopter, you will change your thinking as it " gets to close to home ". Then you will appreciate the concept of gear up or go back down the ladder. We all occupied that space at one time. IMHO it is a precipice that must be avoided for any length of time by making the above choice.
Eric

 

[halocline]

I ran into this exact situation on my second (or third??) dive trip. I was diving on a rented computer, and was diving very aggressively...and didn't understand that my computer was telling me to get the h%ck up into shallower water. So as a reward, I had a 6 hour ride in GC's lovely gas tank. I am ridiculously conservative now, own two computers, but have always worried what a deco stop (on my Sunnto) looks like in real time. You can read the manual all you want, but at least for me, it doesn't stick until I see it live (trust me, this foilable isn't just in diving, either).

Try the dive nav site, I think that guy has some simulators that you can use to view your computer's display animated in various modes.

Have you read an article that explains basic deco theory, how it was arrived at, and what the principles are? There's a chapter in the PADI encyclopedia of recreational diving that does a good job. Having a sense of the ideas of tissue compartments and bubble formation are especially helpful IMO in terms of monitoring and modifying your dive behavior. The computers simply provide data; the safety of your diving is based entirely on your own behavior. We all 'know' this, but having a clearer understanding of what factors the computer is using to arrive at it's calculations puts you (meaning all of us, not 'you' particularly) in a better position to manage your profile. I mention this because to me 'owning two computers' does not necessarily imply conservative diving.

Personally I don't pay a lot of attention to the NDL readout on my computer; I closely look at depth/time and, towards the end of dive, the N2 loading bar graph. I usually surface with the bar graph in the 'green' after a nice long stop at 10 ft.

 

[Lorenzoid]

Been there once.

Did: YOU, WATCH ME, tap dive computer, Signal CEILING above my head, then YOU, STOP (both hands). It worked.

This is pretty much what my dive buddy (wife) and I have agreed to do. But thanks for educating me about the extended pinkie signal. Ideally, I like to signal to my buddy or DM that I only have a couple of minutes of no-deco time remaining and that I suggest we ascend (signaling either "X feet" or an unspecified "ceiling"). My wife and I understand these signals, and I don't care what the DM thinks we're doing when we seemingly break away and ascend a bit.

 

[DevonDiver]

I'm not sure exactly how you distinguish recreational computers from others?

Algorithm - First and foremost, an algorithm specifically tailored for dives beyond traditional NDLs. All things not being linear and constant as depth increases...

Multiple Gas/switching - Ability to switch between multiple (4-8+) tanks/gas mixes on the dive, including rich nitrox for deco.

Helium - Ability to conduct dives with an algorithm that calculates on/off-gassing of trimix/heliox mixes.

If it doesn't do all three of the above, it's a recreational computer... IMHO

I'd like to add ICD considerations to that list of factors/functions also...

 

[navi_jen]

Try the dive nav site, I think that guy has some simulators that you can use to view your computer's display animated in various modes.

Have you read an article that explains basic deco theory, how it was arrived at, and what the principles are? There's a chapter in the PADI encyclopedia of recreational diving that does a good job. Having a sense of the ideas of tissue compartments and bubble formation are especially helpful IMO in terms of monitoring and modifying your dive behavior. The computers simply provide data; the safety of your diving is based entirely on your own behavior. We all 'know' this, but having a clearer understanding of what factors the computer is using to arrive at it's calculations puts you (meaning all of us, not 'you' particularly) in a better position to manage your profile. I mention this because to me 'owning two computers' does not necessarily imply conservative diving.

Personally I don't pay a lot of attention to the NDL readout on my computer; I closely look at depth/time and, towards the end of dive, the N2 loading bar graph. I usually surface with the bar graph in the 'green' after a nice long stop at 10 ft.

Thanks. I will certainly look at that article. I have 2 computers...and whichever goes off first is when I'm heading up. But you are right, I look at the loading bar a LOT on my Suunto and always make sure I'm in the green (the loading graph) for the entire dive. Heck, when I was in Thailand, I actually had it set to S2, the most conservative setting. I might sacrifice some bottom time, but given that I'm not in the best physical shape, I figure better safe than sorry.

Have fun diving, everyone!

 

[boulderjohn]

Algorithm - First and foremost, an algorithm specifically tailored for dives beyond traditional NDLs. All things not being linear and constant as depth increases...

Multiple Gas/switching - Ability to switch between multiple (4-8+) tanks/gas mixes on the dive, including rich nitrox for deco.

Helium - Ability to conduct dives with an algorithm that calculates on/off-gassing of trimix/heliox mixes.

If it doesn't do all three of the above, it's a recreational computer... IMHO

I'd like to add ICD considerations to that list of factors/functions also...

If you don't want to apply all those criteria (and I agree with them), just look at what it says in the computer instruction manual. The recreational computers I know specifically say that they are not intended for planned decompression and should be used for decompression only in cases when it was not intended. The technical computers tell you how to use them for planned decompression.

 

[uncfnp]

Obviously if you are doing multiple gas dives and/or Helium, you need a DC that will handle that input. But for the recreational diver that pushes or crosses NDL's on either conservative on liberal settings, will the average recreation DC safely handle that event in the same way as a tech computer? In others words, when a rec dives goes into "light deco" is he/she adequately covered by their DC when they follow the computers response? At the end of the dive, is that diver on an equal footing as a diver that did the same dive with a tech computer? Are not the underlying algorithms equal?

 

[Bob DBF]

Quote Originally Posted by Bob DBF View Post
You don't have to be violating procedure, sloppy or intentional. Last summer I made two dives to around 120', the first was fine and I did well over an hour SI and a computer check gave me about 8min or so at depth on the second dive. I made the dive and was within NDL by minutes until the neighborhood of 100' at which point I went into deco. I came out of deco around 50' so it was a nothing deal overall however, it was interesting for a while because it was not expected.

Since then I also watch the runtime of my deep dives, because of my SAC, and plan on being above 60' sooner than I would have before. It also added another reason for me not to do deep stops, which would have added to my deco on this profile. This was all done in 53 degree f water and wetsuit, so I was not looking forward to a deco stop. I extended the safety stop 'till my tank was at 200# and still had the pony as reserve.



Bob
------------------------------------
"the future is uncertain and the end is always near"
Jim Morrison

I think that advocating unsafe and dangerous practices is both stupid and foolish. That is why I don't tell people to do what I do. Dsix36

Yes, if you went into deco without planning it then it WAS indeed sloppy. If you planned for it, it was no longer accidental.
Your computer does show how much NDL you have left at any given point and there should be no problem adhereing to it, the same way you do your spg unless you have incidents that have to be resolved before you can start your ascent.

---------- Post added January 7th, 2014 at 06:17 PM ----------

If you know the computer is about to go into deco and still continue, its intentional. It doesnt neccesarilly make it stupid, as long as you know what youre doing, but its definetly not accidental.

Perhaps I didn't make it clear enough, I made the dive to 120' for 4 or 5 minutes, 3 to 4 min to NDL, and went into deco on the way up. At that point I had to continue into deco to end the dive. I guess it was intentional, if intentional means having no choice.

In the grand scheme of things, I plan for deco by bringing extra gas on these dives in case I can't get to the surface as fast as my dive plan. I am not a stranger to deco; although most of mine was in the late '60's and the '70's with double j-valve 72's and later 80's, my memory isn't gone yet.

I didn't feel a need to bring a laptop and buy dive planning software to plan the dive as I had been doing a pair of similar dives each weekend for several weeks without any issue using the planning function of the dive computer. My theory is that I was spending more time coming back upslope in the 100' to 75' range because I had more air reserve than when I started making these dives due to a better SAC. Now I come directly up to 60' before dawdling around, problem solved.



Bob
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I may be old, but I'm not dead yet

 

[boulderjohn]

Obviously if you are doing multiple gas dives and/or Helium, you need a DC that will handle that input. But for the recreational diver that pushes or crosses NDL's on either conservative on liberal settings, will the average recreation DC safely handle that event in the same way as a tech computer? In others words, when a rec dives goes into "light deco" is he/she adequately covered by their DC when they follow the computers response? At the end of the dive, is that diver on an equal footing as a diver that did the same dive with a tech computer? Are not the underlying algorithms equal?

Why wouldn't it? It would not be hard to pick an existing algorithm for decompression and build it into the program. I bought my first computer (a Suunto Cobra) in 1999, and I doubt that the algorithm used for emergency deco in it is any different from the ones being installed by Suunto in their recreational computers today. The tech computers have more planning capacity, etc. than the recreational computers.

 

[uncfnp]

Algorithm - First and foremost, an algorithm specifically tailored for dives beyond traditional NDLs. All things not being linear and constant as depth increases...
...//...

Why wouldn't it?...//...

That was my assumption but given the post by DevonDiver and other comments regarding rec vs tech computers, I wanted to make this concept clearer.