Feedback on recent two-tank and dive limits

[JMarc]

Second, it locked completely preventing anyone from telling the severity.

That point is outside the main topic of this thread and this part "basic scuba" part of the forum as it is about deco, but I see no real good option about what to do when deco obligations are not respected. Locking make it at least clear that there is a problem to be solved, but doesn't give guidance for doing so. What I know(*) of the behavior of non locking computer is not that much better and arguably worse for beginners: indication that there is an issue only while the ceiling is broken, and continue to apply blindly the underlying model. There is a guidance but it is misleading. For instance for ZHL-16C considering that the body outgas more at the swallower depth, taking that increased off-gasing into account and thus reduce the stop time... even additional information like the saturation graph, GF99 and GFsurf will improve as the time at surface increase. The procedures I know (I was taught several along the years) for an interrupted stop where re-immersion is considered an option (that shouldn't be systematic), are to go back down as quickly as possible, increase the non-done stop time, and surely not to consider the time spent above the ceiling as part of the stop. Someone aware of that can adjust, but you need to be aware.

One can easily imagine a computer programmed to provide something better than what they do now.

(*) Important caveat, I don't know about all computers, and their behavior in such circumstance tend to be badly documented and I haven't checked that my memory of what I read is accurate.

 

[old frogman]

Interesting flyfishing exercise so far.

Let' look at a scenario. You have a son or daughter somewhere between 16 and 18 years of age and they have just completed their basic open water course, and you are going to give them an entry level Shearwater Peregrine dive computer or one similar with Buhlman and GF algorithm. What precautions are you likely to take to make him or her safe when using this dive computer? Or are you just going to give him or her the dive computer and just say read the user manual and figure it out.

It appears that divers that have answered directly or in a roundabout way, go with option "a". Which is make their son or daughter safe when using this particular dive computer with the Buhlmann GF algorithm. Most admirable. I would do the same.

A key issue with the Peregrine and others like it is they have a custom GF function so that you may vary the high and low GF to fine tune the stops. Imagine a new recreational basic level diver playing around with this function. The user manual does have a warning label on this function, but the custom function is there and very tempting to try it out. Hell, when I was young, I would have gone custom in an instant.

The real world. Not all new recreational divers coming out of the basic course are going to have a father, uncle, older brother etc. who is an experienced recreational diver or tech diver and who is going to sit beside him and help him or her with understanding and setting up the computer.

If you buy the computer from a shop, the salesperson may give you a quick five-minute explanation. Is that really enough?

Many people today buy their dive computers online. No quick five-minute explanation from a salesperson available. Just the user manual.

 

[David Carron]

For instance for ZHL-16C considering that the body outgas more at the swallower depth, taking that increased off-gasing into account and thus reduce the stop time... even additional information like the saturation graph, GF99 and GFsurf will improve as the time at surface increase.

By "improve" you actually mean "reduce"

The dive computer's behaviour when the diver exceeds the ceiling depth certainly is a problem although there is little to no guidance as to what a more appropriate behaviour would be.

 

[JMarc]

It appears that divers that have answered directly or in a roundabout way, go with option "a". Which is make their son or daughter safe when using this particular dive computer with the Buhlmann GF algorithm. Most admirable. I would do the same.

You keep missing, or at the least not acknowledging, the important fact that we would do the same for any computer. Wouldn't you?

 

[JMarc]

By "improve" you actually mean "reduce"

Yes, the numbers and graphs are indicating a misleading state.

The dive computer's behaviour when the diver exceeds the ceiling depth certainly is a problem although there is little to no guidance as to what a more appropriate behaviour would be.

We are totally on the same page here and I think it is you who made me notice that point.

For others, even without having the computer suggest an action, indicating that the ceiling has been broken, even if it isn't any more, and for how long would be a progress. As for potential actions by the computer, it is easy to come with suggestions which would probably be improvement (applying one of the multiple thumb rules suggested in table manuals, freezing the off-gasing when the ceiling is broken, slowing all off-gasing afterwards by modifying the time constant of the sursaturated compartments, automatically lowering GFs,...) the difficulty is being sure that's effective enough, and when to switch to the medical emergency procedure.

 

[Blackcrusader]

Many people today buy their dive computers online. No quick five-minute explanation from a salesperson available. Just the user manual.

That is how I bought my Shearwater Perdix. Then it was up to me to RTFM. I was no different than a newly certified diver as I had never used a DC with GF's before. Just Suunto RGBM DC's which took much more time to setup and learn than the Shearwater.

So I had a choice, use it in the very simple and easy recreational mode where I did not need to know anything about GF's, just use the conservative preset NDL and deco settings or choose to use the TEC mode and study more about GF settings, no low NDL warnings, no safety stops to clear, and other features.

Thre reasons I bought the Perdix, the great digital display, easy to setup, and that it has a compass.

When I was in the Maldives in May, a Dutch lass with very few dives had a dive computer on her arm. Guess what it was not using GF's. On dives her alarms would go off and she had no clue what they were.
So what difference did it make that she was using RGBM over Bulhman with GFs? Nada nil zip Sweet eff All. She had no clue how her dive computer worked but anyway her BF was a DM so she just followed him till we banned him from our dives.

 

[lizardland]

Many people today buy their dive computers online. No quick five-minute explanation from a salesperson available. Just the user manual.

I've been diving since 1994 and I've never had anyone ever explain how to use a computer when I bought it. But I take your point. You could buy a brand new Uwatec Aladin Pro out the box, strap it to your wrist, go for a dive and have a reasonable idea of a. what the numbers on the screen mean and b. be reasonably confident that the basic default set up works. I've owned a Shearwater and I don't think you could say that about either a or b. Personally, sometimes I feel like they should be publishing recommended GF's like tide tables because advice seems to change so often.

Is a GF computer really a great entry level choice? I think one of the issues is that dive kit is just so expensive now when it comes to the big purchases. People buy based on what they think they'll be doing at some point in the future rather than what they need now because nobody wants or can afford to be buying twice. When I started diving, my first computer was a Suunto Companion that was relatively cheap and upgrading it down the line wasn't really much of a hit. The dive industry seems to have filletted out every single budget option for new divers and I suspect that's a big part of why diving is in decline compared with other sports. You are kind of funnelled into buying stuff that is a hell of a lot further up the ladder than what you really need. Most other sports that I do are pretty good at having equipment options matched to the participants' needs at that moment.

I wonder if that's also a symptom of younger people being more technologically minded: they grow up in a world where they are encouraged to buy the thing with the biggest processor, hard drive, graphics card, etc that they can afford and that doesn't really have any downside.

 

[jborg]

You could buy a brand new Uwatec Aladin Pro out the box, strap it to your wrist, go for a dive and have a reasonable idea of a. what the numbers on the screen mean and b. be reasonably confident that the basic default set up works. I've owned a Shearwater and I don't think you could say that

This is your opinion and you're of course free to have it regardless of facts, but I'd be curious if it's based on anything except familiarity and nostalgia?

 

[Belzelbub]

So far no one has answered this simple scenario question which is designed to test my point of view. All I have seen so far is various persons kicking the can down the road, going off on different tangents extolling the virtue of the Peregrine or the value of GUE basic recreational dive course.

I agree the Peregrine and Buhlmann GF is a great unit. But should it be in the hands of the newly certified recreational diver, as per the scenario question.

Perhaps you have me on ignore. I did answer your question.
I have actually purchased Peregrine TXs for my children. My oldest is pretty experienced, but my youngest daughter is still relatively new. I see absolutely no reason why this wouldn't be a good choice for a new diver. They are more expensive than some other options, but quite comparable when looking at other computers with similar features.

As they are my children, I explain the basic functions and encourage them to read the manual, but that's it. I would say less instruction needed with the Peregrine vs. the Oceanics.

And I know you won't like this, but you refuse to answer a question that has been posed to you multiple times. If you want people to take you seriously, maybe you should answer it. I'll repeat it below.

What is the difference between a new diver selecting Low, Medium, or High conservatism on a Peregrine (or other Buhlmann DC with GFs) vs. a new diver selecting Low, Medium, High or L0-LX conservatism settings?

 

[crofrog]

3) OK, so you violate your NDL, what happens next?