Dive Computer No Deco Computations Question

[beldridg]

I'm someone who deals in trade-off and not absolute. The lock out seems a sensible option depending on the circumstances. And the more you insist on simple options because we are in Basic Scuba, the more sensible it looks along with the user guide instructions of going to 5 meters and empty your tank.

As somebody whose dives almost always include deco, I'm not sure I agree with that.

For example, let's say that you're at 20m/70' on a 5 minute stop and you end up slightly above that stop for whatever reason for 3 minutes and the computer goes into violation mode.

I should now go straight to 5m and not attempt any stops in between? That seems like it is only going to compound any potential problem.

I voted with my wallet.

I sent the DX back and won't ever dive Suunto. I dive Shearwater because I like the fact that it will never lock me out and I consider it a superior product for decompression diving.

Suunto might be an okay computer for recreational diving (although I personally still wouldn't use it), but I can't remember that last time I saw anybody who does any level of decompression diving using one.

Regards,

- brett

 

[runsongas]

@dmaziuk for that incident, it may still have been the right call to skip the IWR because he was alert and seemed to be doing well during his chamber treatment. the problem was something happened later and he got into medical trouble but the medical professional had left with only an unqualified trainee who wasn't experienced enough to deal with the emergency still watching him.

 

[dmaziuk]

@dmaziuk for that incident, it may still have been the right call to skip the IWR because he was alert and seemed to be doing well during his chamber treatment. the problem was something happened later and he got into medical trouble but the medical professional had left with only an unqualified trainee who wasn't experienced enough to deal with the emergency still watching him.

I think a) if you have an hour of deco, you probably have significant gas loading in the slower compartments that may be expected to take longer to bubble out and cause symptoms, and b) losing feeling in the legs on the way to the chamber wouldn't be my definition of "doing well".

But my point was, "better bent than drowned" is an excellent rule as long as you are, in fact, drowning. Scenarios posited in this thread are more like "I overshot my ceiling for more than 3 minutes"-- that argument does not apply.

 

[runsongas]

it sounded like from the article posted in the A&I thread that that resolved as the chamber treatment started

 

[David Carron]

I dive Shearwater because I like the fact that it will never lock me out and I consider it a superior product for decompression diving.

It's certainly true that, like all "pure" ZHL machines, a Shearwater will always display an ascent profile. The downside to this is that it may under some circumstances display a dangerously incorrect one.

 

[crofrog]

It's certainly true that, like all "pure" ZHL machines, a Shearwater will always display an ascent profile. The downside to this is that it may under some circumstances display a dangerously incorrect one.

Can you back up your assertion with empirical data or research

 

[David Carron]

Can you back up your assertion with empirical data or research

For the purposes of comparison here's two profiles: the blue one descends to 50m and stays there for 20 minutes. The red one descends to 50m then after fifteen minutes rapidly ascends to the surface at 50m/min, stays at the surface for two minutes then redescends to 50m.

ZHL16 GF50/80 calculates 45 minutes of TTS with stops starting at 18 metres for the well-behaved blue profile but only 35 minutes of TTS with stops starting at 9m for the red profile with its rapid ascent and ceiling violation.

ZHL16 does not claim to calculate safe ascents for profiles outside of its parameters, and I do not know what the safest ascent profile for the red dive is (nobody really does) but it doesn't seem super-contentious to claim that it's neither shorter nor shallower than ZHL's prediction for the blue profile.

 

[Belzelbub]

I'm someone who deals in trade-off and not absolute. The lock out seems a sensible option depending on the circumstances. And the more you insist on simple options because we are in Basic Scuba, the more sensible it looks along with the user guide instructions of going to 5 meters and empty your tank.

I'll never get around to the idea that an in-water lockout is ever a good thing. I got a computer to provide information throughout the dive. My computer should not throw a tantrum and give me the silent treatment while in the water. I'm not a fan of post-dive lockouts either, but I understand that a little more.

I still think they are ineffective as there are plenty of stories of divers doing dives in gauge mode because they locked out their computer.

It's certainly true that, like all "pure" ZHL machines, a Shearwater will always display an ascent profile. The downside to this is that it may under some circumstances display a dangerously incorrect one.

I know you've done more research on this than I. However, I'd still prefer a computer that will do its best to provide information during the dive. Perhaps not ideal, but IMO better than providing no guidance to stops at all.

 

[JMarc]

I'll never get around to the idea that an in-water lockout is ever a good thing.

The more one argue that this is Basic Scuba and that the public don't know anything about deco, the more a lock out look sane (*). It is less so for people who know more what they are doing, the limits of deco algorithms and what could be done when they are overstepped. Yet, I'd appreciate a more noticeable and permanent info that the known validity envelop has been broken.

And it seems to me that, whatever is the public, giving a reduced deco obligation compared to the original one can't be sanely considered as a best effort (the substance of the comment which made me participate in this thread), it has far too many caveats.

(*) it may be ineffective. But I wonder what would be more effective (yes, my faith in humanity is low). Better training is the only answer I have. The fact that occurrence of DCS and its gravity is random and linked with the person and the circumstances encourages complacency when infractions have no consequences. Until they do.

 

[Belzelbub]

The more one argue that this is Basic Scuba and that the public don't know anything about deco, the more a lock out look sane (*).

There is a big difference between in-water lockout and a post-dive lockout. I understand the reasoning for post-dive lockout. I don't currently dive with any computers that will lockout, but that's a personal choice.

I agree that there are divers that won't follow a computer. These should not be the divers that a manufacturer designs their product around. Those likely can't be helped regardless of the level of tech applied.

It is less so for people who know more what they are doing, the limits of deco algorithms and what could be done when they are overstepped. Yet, I'd appreciate a more noticeable and permanent info that the known validity envelop has been broken.

Regardless of level of knowledge on deco algorithms, the computer should be designed for those divers who are willing to check it periodically, understand what it is telling them, and do their best to follow the guidance. There must be better options than to turn off that guidance during a dive when a parameter was not met to the satisfaction of the programmers.