Features request : switching GF underwater

[maran]

hello,
It would be good to have a possibility to switch gradient factor underwater. For example in case of losing the consciousness of my buddy I would like to go up on different settings than normally.

[gorcio]

I guess you will have something else and more urgent to do when you buddy loses consciousness than playing with your computer settings

[swissdiving]

Does such a request even warrant an answer?

[maran]

It was only an example. Maybe I will be in a hurry not to be late for dinner
Competitive company sees the need of such option (Shearwater Predator).

[tiefunten]

Why do you need to change GF then? The OSTC shows the gradients during decompression - just decompress as long as you are within the limits you want to risk!?

[swissdiving]

Maran,

You really need to come up with better examples.

Although I might be mistaken and would not claim to be an expert on Shearwater products, but I could not find any reference in the Shearwater Predator or Petrel manual on changing GF's during the dive.

But I am sure you can correct me in this regard.

[sailor]

swissdiving Wrote:
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>
> You really need to come up with better examples.
>
>

running out of gas ( e.g. bailout )

[swissdiving]

I am no CC diver, but even with CC, is changing the GF in a situation like this the fore most thing on your mind?

[smcmullan]

Perhaps I understand the scenario

I dive with the OSTC as my secondary decompression computer.

My primary computer is an Inspiration Vision. It uses Buhlmanns algorithm and i've set the GFs to 15/85.

The OSTC I primarily use for an emergency. Under these circumstances I want to be able to switch it to open circuit bailout and get the hell out of depth as quickly as possible before I run out of bailout gas but i do want to have *some* schedule to *reduce* the risk of DCI but *improve* the chances of survival. For this reason i have the OSTC set to buhlmann without GFs.

However what would be real nice is if I could use the OSTC in CC mode with 15/85 to confirm the primary computer and then if I bailout (and have to assume I've lost the Vision computer at that stage) to use a different set of GFs to get me shallow fast.

So maybe thats what maran is suggesting-ish i.e. to have two distinct sets of preprogrammed gfs - one for normal plan and another for emergency ascent due to gas shortage. This could also be applicable to open circuit divers.

[swissdiving]

Hi SMC,

Ok, your example makes a lot more sense than Marans. I am still not 100% convinced. Why would you loose your vision computer? What is the liklyhood that such a situation would occure?

I may be mistaken, but I would have thought that the dive has to be planned AND dived in such a fashion that you never get in to a situation where you would not have enough bailout gas to get you to the surface safely (within the profile give by using GF 15/85)?

[smcmullan]

I guess we're heading towards some of the more challenging diving scenarios Hansjoerg.

If a rebreather floods that is one of the scenarios where you definitely have to bailout to open circuit. There is a significant chance in those circumstances that the electronics will be compromised by the salt water. Its never happened to me but I plan for it regardless. I did witness a dive buddy losing his rebreather electronic display at 90m 2 years ago so it does happen.

With the depths and bottom times that we are diving here (115m for 30mins bottom time with 4-5 hour runtime is not unusual at all) we simply do not carry enough open circuit gas to do an "ideal" decompression in the case of an emergency so the philosophy is to get shallow fast, get access to more deco gas deployed from the boat via emergency drop sets and "mend the bend" as much as possible. Our belief is that getting a mild type I or even type II DCS hit is better than drowning due to lack of gas. You may ask why we do not carry more gas but the answer is simple - carrying so many cylinders would lead to even more problems with CO2 with the exertion of swimming at depth.

If you want a nice example then I've been at 125m with two bailout cylinders ali80s with 10/70 and 20/35. That single ali80 of breathable gas 10/70 won't last very long at that depth. Buddies can help of course and even teams of three (cave style) are better options but you get the idea that even among three divers its hard to carry enough gas to even get one bailed out CCR diver out with an "ideal deco profile" from those depths.

Of course in this scenario I'm not even bothering to change my computer - not even to OC bailout mode. My first priority to get to my first gas switch asap and then I'll change the computer, send up emergency yellow bag, get access to additional gas from the emergency drop sets deployed by the boat etc. I'd still want to forget all the deep stops of a 15/85 schedule and get shallow even at that point.

This sounds like an extreme example (and it is, thats just the reality of exploration diving?) but maybe there are some other examples from slightly more regular diving which might generally justify an "emergency ascent" feature which changes the deco profile to get rid of deep stops. I don't know - I guess thats the point of the discussion.

[swissdiving]

Stephen,

Although I am not a CC diver, I am very much aware what the reasons behind your example are and expected an answer along your lines.
The question I would pose is what the liklyhood of your scenario actually is. Are vision computers really this likely to flood?

As you say, we are talking here about emergency situations. If you are very likely to run out of air, are you really going to have time or are you really going to be capable of changing the GF to a more aggressive scenario?
Would it not make much more sense to pre-configure a second GF setting/profile (an emergency profile) that can be chosen in a situation like this? The less fiddling with the dive computer in an emergency situation the better.

[gorcio]

While pre-programmed GF set(s) seem to be making a bit more sense to me, I'd still think that in such extreme situation, the best for "mend the bend" is to follow a pre-prepared plan. If you really take such scenario into account, given depth and time - nothing stops you from having a plan ready and calculated based on your assumptions (different GFs, pure Buhlman, etc). I have never done a dive like that as I am an OC diver, but isn't bailing out a case of lost gas (back-gas) in OC, for which you need to have a plan ready ? Even if the emergency plan is not to carry sufficient supply and follow emergency callout to surface for additional drop of gas, you can surely pre-plan emergency case of leaving your depth on much more aggressive profile ?

[smcmullan]

I'm probably not the right person to be arguing for this feature because perhaps my application is specialised. Just some notes that might help to clarify my perspective:

1. I'm already using the OSTC without GFs - thats aggresive enough for my bailouts. So its set in "emergency mode" for me by default. The advantage for me with this feature is that in normal mode with GFs applied I could use the OSTC as a sanity check to the normal operation of the Vision.

2. I can't answer your question Hansjoerg about are Vision computers likely to flood (or better stated have an electronics shutdown). So much of what we do in tech diving is based on redundancy for hypothetical situations so this another.

3. Yes, I'm talking about two sets of pre-programmed GFs rather than the ability to change from say 15/85 to some arbitrary value in the water. I just don't see an application for that. The only way I could rationalise maran's suggestion was to have normal ascent mode/emergency ascent mode as an on/off situation.

4. Gorcio, again I can't really adequately answer your planning question. Most dives I do the bailout scenario is perfectly plannable, there is enough gas. On others you can plan all you want and the answer comes back the same: you don't have enough gas and you don't own all the cylinders you need and even if you did you would not be able to attach them and stand up or swim. There will be delays to any plan e.g. deploying smb, perhaps you decide to follow the transit line to the deco station because there are divers there with more gas, or there is a delay getting the drop sets from the boat. Yes we can plan in advance but my opinion is the whole point in having a computer is to assist and deal with things that go beyond the plan. If I didn't believe that then I would be happy to dive with two depth timers and a set of tables and no need to buy an OSTC


But I really do have to go back to point 1. I'm happy with my emergency computer. Its just a shame I can't use it in "normal" mode

I think other divers should comment as to whether they would use an "emergency ascent" feature. I think that would perhaps be more relevant to this discussion.

[swissdiving]

I tend to agree with gorcio and would even go a step further and query the fact that with CC diving the limits of what is safe are pushed a lot more. Diving CC has the advantage that the limitations of OC can be overcome, the problem is that in an emergency OC is the only backup, with its inherent limitations.

I believe that it is no coincident that recently quite a number of cave diving fatalities included CC equipment (not necessarily because of OoO)...

ADDENDUM
(and I know I am most probably am beeing controversial. Since I posted this comment Stephen has made a new comment in which I agree with him that it would be good to hear more from other divers).

[Olaf70]

I lost my vision computer completely on a dive. And the nice thing was solenoid went full open on me and the lights were nicely green.
Good reason to bailout. But then I want to switch between normal bailout and agressive bailout. Don't know how I will react wen things go wrong.
That time everything has been fine.
But I have multiple stories of people wo had a sac rate of 60 to 90 liters /minute. That is the moment that you want an agressive bailout.

[swissdiving]

It seems to me that the solution is not a more agressive GF but a dive computer other than the vision, that is more reliable (are you talking about the X1).

What about the DR5?

[heinrichsweikamp]

I think it would be required to display the GF pair in the divemode screen. And I also think that one additional GF pair (Pre-configured before the dive) is enough.

Regards,
Matthias

[gorcio]

Pardon me, gents, but allow me to play devil's advocate.
If you go for a second GF set, pre-programmed (which sounds much better than modifying GFs under water, which I had already mentioned), you need to get it somehow (=calculate ?). That emergency set will not turn up out of the blue, right ? Aggressive or less aggressive - you would have to know how it will work, I assume. Knowing that set already before the dive, you can prepare an emergency plan with accordance to that GF set. Just had a minor emergency with a partner yesterday, on relatively shallow dive (40m) and I can tell you that the only thing I wanted from my computer at the time of assisting him up, was to display depth, time, and ascent rate when we got closer to surface.

[swissdiving]

Gorcio (tu)

[smcmullan]

Guys, with respect if you're offering up examples of a 40m dive and agreeing with the example then I'd suggest you've completely missed the point of this potential feature.

Likewise suggesting that the OSTC is somehow not capable or suitable of having this functionality and users should consider a X1 or DR5 shows a lack of understanding.

Perhaps consider what Ross Hemingway wrote about the Fast Bailout Option of V-planner here: http://www.rebreatherworld.com/decompre ... l-out.html

The OSTC is already most of the way there. There is already the ability to choose between Buhlmanns algorithm and Buhlmanns algorithm with GFs applied. The only thing that is missing is the ability to switch between these options (quickly please!) and recalculate the profile underwater.

[dmainou]

Guys,

The predator allows the diver to change both the high and low GF during the dive.
It also allows the diver to adjust the setpoint during the dive.
And to have the setpoint changed automatically at certain depths.

Now that the petrel costs about the same as the 2n... It would make sense to provide the same functionality.

For those that do shallower dives. I'm sure that there will be the odd dive where you'd like to extend the deco schedule. If you have the ability to do so it would at least allow the diver to extend the stops with some sort of accepted rationale. If you are feeling a bit uneasy and you have the gas... it makes sense to stay down there a bit longer.

I agree with Stephen in that I'd like to confirm the deco calculations of the predator with the open source and independently verified HW calculation (standard GF) and if the sh!t hits the fan I'd like to be able to change to a bailout GF and exit acoording to that plan.

Further to this. If the only thing that happened is that the controler died but still have access to the HUD then I have no need to exit the water following the bailout GF. I simply need to follow the schedule as recommended by the base GF on the HW device.

I hope it makes sense.

D

[heinrichsweikamp]

Hi,

An alternative GF set (We have this feature in the DR5, for example) makes sense for deeper dives (40m is not deep) with hours of deco to go.
I don't care what other computers offer, I thing we can easily list dozens of OSTC features other computers don't offer.

To implement this switch we need:
a) show the GF pair somewhere
b) add a menu entry to switch it

Ideas, anyone?

regards,
Matthias

[gorcio]

smcmullan Wrote:
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> Guys, with respect if you're offering up examples
> of a 40m dive and agreeing with the example then
> I'd suggest you've completely missed the point of
> this potential feature.

I admit. I missed the point. And in fact I did not offer any example, it was actually counter-example - I did not want to change anything on my computer. You probably missed that point. Not every one here is doing only deep dives every day - I happen to go out quite often with those who still dive air, can you imagine ? and on OC, not CC - they still exist and if fact they will remain majority for a while. My point was about planning and pre-dive preparation of runtime. If you want such function - I don't mind, as I won't use it, because, back to my point, if I spend time before diving to calculate a second set of GFs, I may as well spend a bit more time to calculate emergency profile(s) on that GF set and write it down, instead of relying on the unit. I hope you would agree that the second set of GFs has to be somehow calculated and not just invented out of the blue on the bases of "let's take the base GFs set and modify GFlow by XX% and GFhigh by YY% cause I feel like it looks good on display" ?

@Matthias :
position - above current mix ? (kill me, I do not remember by heart what may be displayed there)
menu - in the dive menu, at the bottom since it will be likely the least frequently used function ?

[DTR.Diver66]

Hello Matthias,

the display for the current GF-pair during the dive in the lower right menu, as average depth, future TTS and others. The ability to change over the top menu as gas list and Decoplan.


Regards (tu)