Now it's time to choose a wrist computer.

[scubadada]

If your plan is a no stop dive, I believe you should follow the NDL plan on the computer you have chosen to use, with the conservatism setting you have selected. By remaining below the NDL, you will avoid ever having to deal with a potential missed deco stop.

However, this topic has been discussed on numerous previous occasions. All deco stops are not created equal. This is a 1st clean dive on air to 60 ft. NDLs come from my Shearwater Teric running Buhlmann ZH-L16C, and my Oceanic Geo 2, running both DSAT and PZ+. The NDLs vary widely, from 32 to 57 min. If you were to dive GF 35/75, 40/85, 45/95, or PZ+ to the DSAT NDL of 57 min, you would accrue deco time, somewhere between 17 and 3 min

So, all of these dive times on air at 60 feet are "safe". DSAT is the basis of the PADI Recreational Dive Planner, in use since the late 1980s. It is also the basis for the DSAT decompression algorithm used in Pelagic Pressure Systems computers almost as long.

It makes intuitive sense that a longer exposure should increase your risk for DCS. There is a probabilistic decompression model, SAUL, that has previously been discussed on SB. It allows one to estimate that risk Modern Decompression These are the same exposure times for a first, clean dive to 60 feet on air shown above. The dive times are ranked by probability of DCS, % and chance. SAUL includes a 3 min safety stop.

I hope this has given some of you something to think about. I've been thinking about this topic for quite a while

See the post by @dmaziuk Now it's time to choose a wrist computer. "...it's not really about "safe": it's about risks you're willing to take".

 

[Belzelbub]

Is a 24 hour lock out really necessary? That's what I'm asking. Keeping with the scenario of having to skip a "mandatory" stop due to a legitimate threat of immanent bodily injury, at what point does the risk of DCS become more of a concern than losing dive time? Again, this is honest inquiry, not a challenge.

Fair enough question. If you blow all your stops sitting out the next days dive is certainly wise. I’m more talking about minor discretions, like cutting a stop short. If that doesn’t meet the requirements, some computers will lock you out for the 24 hours. Probably doesn’t warrant 24 hours, but sitting out the next dive or remainder for the day is a good idea. But, I don’t know of any computer that does a shorter lockout.

Another option is to give the diver lots of information, and let them make the decision based on that information. An example would be the tissue loading bar graph. The diver could use that to monitor their tissue compartments to see where they are compared to Max saturation. Then, if the diver decides to do another dive, the computer dives with them. A locked out computer essentially turns it’s back on the diver.

 

[scubadada]

It's not perfectly straightforward. It is quite easy to tilt the odds in your favor. I dive two computers, An 11 year old AI Oceanic VT3 running DSAT and a 2 1/2 year old Shearwater Teric, running 80/95. The majority of my dives are no stop, though often close to NDL. About 5% of my dives are light deco. I dive the more conservative of my two computers or clear one or both for deco.

Before the Teric, I did a 5 min SS if I was close to NDL. I also padded my deco stop by 3-5 min. Now, with the Teric, I follow SurfGF. Neither the set GF, in my case 80/95, or SurfGF takes a SS into account. So, already, you will be reducing your surfacing GF. The majority of my dives end with a SurfGF below 80, even a SS is probably not needed. For the no stop dives close to NDL and the light deco dives, I wait to surface until my GE is in the low 80s or below. Since diving with the Teric, my average surfacing GF has only been 55, with a range of 13-80. My diving ends up being more conservative than I would have thought . It's the risks you're willing to take.

 

[Belzelbub]

5."Lock out"? Some divers just do not pay attention or even understood what the computer was telling them. Good or bad idea is debatable. I have no problem with it.

That’s a very good point. Many divers don’t really understand how to operate their computer or what it is telling them. I’m not sure that they would pick up on “ViOl” or that it’s now in gauge mode as they are ready to splash. In those cases, I’m not certain that either approach is good. The computer that continued to track would probably provide the chamber doc a bit more information.

 

[Gareth J]

It's not perfectly straightforward. It is quite easy to tilt the odds in your favor. I dive two computers, An 11 year old AI Oceanic VT3 running DSAT and a 2 1/2 year old Shearwater Teric, running 80/95. The majority of my dives are no stop, though often close to NDL. About 5% of my dives are light deco. I dive the more conservative of my two computers or clear one or both for deco.

Before the Teric, I did a 5 min SS if I was close to NDL. I also padded my deco stop by 3-5 min. Now, with the Teric, I follow SurfGF. Neither the set GF, in my case 80/95, or SurfGF takes a SS into account. So, already, you will be reducing your surfacing GF. The majority of my dives end with a SurfGF below 80, even a SS is probably not needed. For the no stop dives close to NDL and the light deco dives, I wait to surface until my GE is in the low 80s or below. Since diving with the Teric, my average surfacing GF has only been 55, with a range of 13-80. My diving ends up being more conservative than I would have thought . It's the risks you're willing to take.

80/95 to me looks very aggressive. I may be wrong, but I wouldn't dive that setting.

I prefer the stop penalty over attempting to get out within an aggressive NDL setting.
Potentially, the difference is that the UK culture is to plan the dive and do the stops if you want the depth/bottom time, rather that run an aggressive profile to allow you to dive within the NDL.

I can still remember divers picking up secondhand monitors, because they cut the deco short. The down side was the high risk of a helicopter ride to the chamber. I preferred the extra 10 minutes in the water.

Most of my dives are really conservative anyway, I dive a CCR, but dive mostly with OC buddies. So as a general rule, my buddy requires stops when I am well within my NDL time. Occasionally I get caught our, I had a week on OC when I lost a cell in Scotland during October.

 

[dmaziuk]

Who said they don't "continue to track"? -- I have never seen a log downloaded from one of those locked-out computers, but from the programming perspective there is no reason to stop polling the sensors and recording time and pressure.

In fact some of them (Oceanics, at least) will go into "violation gauge mode" that'll keep showing current depth, time, etc. My Cressi Leo's manual says it'll "cease to function" but I'm not entirely certain what's gonna actually happen on the dive: I've caught its manual glossing over finer detail in other places and not displaying depth would be a really stupid thing to do in that situation.

 

[scubadada]

80/95 to me looks very aggressive. I may be wrong, but I wouldn't dive that setting.

I prefer the stop penalty over attempting to get out within an aggressive NDL setting.
Potentially, the difference is that the UK culture is to plan the dive and do the stops if you want the depth/bottom time, rather that run an aggressive profile to allow you to dive within the NDL.

I can still remember divers picking up secondhand monitors, because they cut the deco short. The down side was the high risk of a helicopter ride to the chamber. I preferred the extra 10 minutes in the water.

Most of my dives are really conservative anyway, I dive a CCR, but dive mostly with OC buddies. So as a general rule, my buddy requires stops when I am well within my NDL time. Occasionally I get caught our, I had a week on OC when I lost a cell in Scotland during October.

I guess you did not read my posts. The majority of my dives are no stop. Only about 5% of my dives are light deco, mostly under 10 min, always under 15 min. You probably also missed my post about SurfGF and surfacing GF.

Enjoy your diving

 

[SaltyCracker]

If your plan is a no stop dive, I believe you should follow the NDL plan on the computer you have chosen to use, with the conservatism setting you have selected.

That was an informative post, thank you.
I was wondering if a conservative setting of 4 might be a little too aggressive, even for a cautious beginner with his trusting child in tow. You don't think so? And on double checking, its range is 0-5, so six levels. I have to assume even a setting of 0 is still "safe" but more likely to include stops correct?

 

[SaltyCracker]

Fair enough question. If you blow all your stops sitting out the next days dive is certainly wise. I’m more talking about minor discretions, like cutting a stop short. If that doesn’t meet the requirements, some computers will lock you out for the 24 hours. Probably doesn’t warrant 24 hours, but sitting out the next dive or remainder for the day is a good idea. But, I don’t know of any computer that does a shorter lockout.

Another option is to give the diver lots of information, and let them make the decision based on that information. An example would be the tissue loading bar graph. The diver could use that to monitor their tissue compartments to see where they are compared to Max saturation. Then, if the diver decides to do another dive, the computer dives with them. A locked out computer essentially turns it’s back on the diver.

I feel like I'm pointed in the right direction now, than you. Now that I have a better understanding, I can see myself adding a tech style computer that logs like this when it comes time to add back-ups to the inventory.

 

[Belzelbub]

Who said they don't "continue to track"? -- I have never seen a log downloaded from one of those locked-out computers, but from the programming perspective there is no reason to stop polling the sensors and recording time and pressure.

Good point. I haven’t seen a log either. My understanding was that they stopped tracking O2 and N2 and functioned as a bottom timer. Not sure if they still log the dive though.

In fact some of them (Oceanics, at least) will go into "violation gauge mode" that'll keep showing current depth, time, etc. My Cressi Leo's manual says it'll "cease to function" but I'm not entirely certain what's gonna actually happen on the dive:

Yes, but in gauge mode, they are not doing anything with the algorithm. To your point, they may still record depth and time, or they may just record max depth and time, or nothing. I took a look at an Oceanic manual, and it did not mention either way.