Decisions on a Dive Computer

[Belzelbub]

See.

Function at 100% hmmm…

Competent? Just missed some stops and wants to dive again?
Responsible? No kids, no buddy, no other divers having their day spoilt by an early return or visit from a helicopter?

I was referring to the DC functioning at 100%, not the diver. A DC that doesn’t lock out will continue to function just as it would before the violation. The algorithm continues to track tissue compartments and provide up to date information should the diver decide to ignore the advice. With a computer that locks out, it only operates in gauge mode during lockout. The algorithm won’t track tissue compartments any more.

I didn’t say the diver was competent or responsible. Only that the dive computer makes that assumption and continues to provide information, or it doesn’t.

 

[Wibble]

I was referring to the DC functioning at 100%, not the diver. A DC that doesn’t lock out will continue to function just as it would before the violation. The algorithm continues to track tissue compartments and provide up to date information should the diver decide to ignore the advice. With a computer that locks out, it only operates in gauge mode during lockout. The algorithm won’t track tissue compartments any more.

I didn’t say the diver was competent or responsible. Only that the dive computer makes that assumption and continues to provide information, or it doesn’t.

Examples that really grated when I used it; typical dive to say 30m/100' for 45mins. Have 80% to deco out on. Max dive time 60mins. Follow the Shearwater which clearly shows the TTS (time to surface) and the dive time; add one to the other and you know how long the dive time will be. When the sum of the two gets to 58mins (e.g. ~15mins TTS), time to put the bag up and leave. Shearwater clears deco fine but the stupid Suunto wants more time.

Do you: hang around and annoy the skipper, or do you bend the stupid Suunto even though the Shearwater's as happy as Larry?


For longer, deeper "tec" dives (60m/200') the Suunto would want at least 10 mins more despite being set on the most "aggressive" setting. BTW I use ZHL-16 with GF 50:80, so not at all aggressive.

 

[Belzelbub]

Shearwater clears deco fine but the stupid Suunto wants more time.

Do you: hang around and annoy the skipper, or do you bend the stupid Suunto even though the Shearwater's as happy as Larry?


For longer, deeper "tec" dives (60m/200') the Suunto would want at least 10 mins more despite being set on the most "aggressive" setting. BTW I use ZHL-16 with GF 50:80, so not at all aggressive.

Yeah, that’s another issue. More closely related to the algorithm, but the lockout does come into play.

You followed the advise of a reasonable computer, but the extremely conservative Suunto disagreed. If that’s on dive 1 of the day, or you have dives for the next day, the Suunto just eliminated itself from use as a backup on those subsequent dives. That’s a real good case for why it’s better to continue to track rather than locking out for an arbitrary timeframe.

 

[KenGordon]

Examples that really grated when I used it; typical dive to say 30m/100' for 45mins. Have 80% to deco out on. Max dive time 60mins. Follow the Shearwater which clearly shows the TTS (time to surface) and the dive time; add one to the other and you know how long the dive time will be. When the sum of the two gets to 58mins (e.g. ~15mins TTS), time to put the bag up and leave. Shearwater clears deco fine but the stupid Suunto wants more time.

Do you: hang around and annoy the skipper, or do you bend the stupid Suunto even though the Shearwater's as happy as Larry?


For longer, deeper "tec" dives (60m/200') the Suunto would want at least 10 mins more despite being set on the most "aggressive" setting. BTW I use ZHL-16 with GF 50:80, so not at all aggressive.

Plan the dive, dive the plan. If you have two computers you will need a plan that works for both.

 

[KenGordon]

I was referring to the DC functioning at 100%, not the diver. A DC that doesn’t lock out will continue to function just as it would before the violation. The algorithm continues to track tissue compartments and provide up to date information should the diver decide to ignore the advice. With a computer that locks out, it only operates in gauge mode during lockout. The algorithm won’t track tissue compartments any more.

I didn’t say the diver was competent or responsible. Only that the dive computer makes that assumption and continues to provide information, or it doesn’t.

You are assuming that the tissue tracking is still applicable after the m-value line has been crossed. Is it? How do you know? Did Buhlmann test that?

If divers miss stops they ought not to be diving again, they should be getting first aid and monitored.

it is actually quite hard to bend a computer, you have to try quite hard.

 

[Belzelbub]

You are assuming that the tissue tracking is still applicable after the m-value line has been crossed. Is it? How do you know? Did Buhlmann test that?

You can incur a deco stop well before the m-value has been crossed depending on how the GFs are set. I do believe the computer will at least track to the m-value line.

If divers miss stops they ought not to be diving again, they should be getting first aid and monitored.

I totally agree, but that’s not up to you, me, or Suunto to decide for another diver.

it is actually quite hard to bend a computer, you have to try quite hard.

Well, that depends on the particular computer, algorithm, and settings.

 

[KenGordon]

You can incur a deco stop well before the m-value has been crossed depending on how the GFs are set. I do believe the computer will at least track to the m-value line.

I totally agree, but that’s not up to you, me, or Suunto to decide for another diver.

Well, that depends on the particular computer, algorithm, and settings.

Of course it is up to Suunto. People pay them to do that.

It is also up to buddies, DMs and everyone involved with a dive to prevent dangerous behaviour. I am not getting back in the water with someone who cannot control themselves and might be in the early stages of getting bent. Why should I take that e tra risk? When managing diving I am responsible to keeping everyone safe. I cannot allow a buddy to take that risk. That is what you have management.

 

[Centrals]

Computer dive is easy and straight forward as long as you follow the instruction.
Read the manual and make sure you understand everything it said.
Never ever dive to the limit, always give yourself some leverage especially on ndl!
Deco dive is entirely different story.
"Accidental deco" = you were not checking your ndl!!!!

You can "bend" a computer but it never suffers DCS!

 

[Wibble]

it is actually quite hard to bend a computer, you have to try quite hard.

Hmmm...

Couple of things. Suunto's proprietary algorithms are very conservative, even in their most aggressive setting. It will lock out "be bent" if you've just one second remaining.

When doing decompression dives with Buhlmann / ZHL16, you choose your gradient factors. Most people don't adjust them, but there's a lot of scope for tweaking the profile. If you're diving 50:80 and you've done most of the deco, but need to cut it short by a few percent (using percent instead of absolute here) you may find that your actual GF is standing at 85%. It's perfectly safe to end the dive at this point, but statistically you're reducing the contingency by using a slightly more aggressive profile.

Changing from 50:80 to 50:85 will knock off some time from the last stop and it's up to the diver to consider the options. Indeed many rebreather divers will plan to do this if bailed out and are short of gas. On the Shearwaters you can see the current GF -- kind of 'fun' to watch this slowly reduce from hundreds of percent down to your target (not much else to do on deco!).

Suunto computers don't allow for any of this in-water plan changing. They're utterly dumb and totally fixed. Almost as if they're designed and built by people who don't actually dive.

Oh, another example is that you've changed your gas during the dive (or forgot to set it correctly), maybe because you've got a different stage cylinder - the Shearwaters will allow you to configure the gas, Suuntos expect you to climb out and restart the dive.

 

[KenGordon]

Hmmm...

Couple of things. Suunto's proprietary algorithms are very conservative, even in their most aggressive setting. It will lock out "be bent" if you've just one second remaining.

When doing decompression dives with Buhlmann / ZHL16, you choose your gradient factors. Most people don't adjust them, but there's a lot of scope for tweaking the profile. If you're diving 50:80 and you've done most of the deco, but need to cut it short by a few percent (using percent instead of absolute here) you may find that your actual GF is standing at 85%. It's perfectly safe to end the dive at this point, but statistically you're reducing the contingency by using a slightly more aggressive profile.

Changing from 50:80 to 50:85 will knock off some time from the last stop and it's up to the diver to consider the options. Indeed many rebreather divers will plan to do this if bailed out and are short of gas. On the Shearwaters you can see the current GF -- kind of 'fun' to watch this slowly reduce from hundreds of percent down to your target (not much else to do on deco!).

Suunto computers don't allow for any of this in-water plan changing. They're utterly dumb and totally fixed. Almost as if they're designed and built by people who don't actually dive.

Oh, another example is that you've changed your gas during the dive (or forgot to set it correctly), maybe because you've got a different stage cylinder - the Shearwaters will allow you to configure the gas, Suuntos expect you to climb out and restart the dive.

So if you are diving in a less than planned way the knobs on the Shearwater let you make stuff up as you go along.

is that what you want millions of people doing? Or do they need an absolute line to conform to? If the only thing making some of them pay attention to their computer is the prospect of sitting out a day then is that bad?

I have never messed with my gas in the water with a Shearwater. I set the gases I might use before I get in and then choose one of the available ones. Just as I do on a Suunto. I find that diving CCR 50/80 or 50/85 with buddies using Suunto p-2 comes out close enough to do the Markgraf.

All over the real world there are people diving Suuntos and having a fine time.