Reference or Backup mode?

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boulderjohn

Technical Instructor
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All my decompression diving has been based on either ratio deco or V-planner, so I have close to no experience with technical diving computers. I hope this is not too easy a question.

I recently did several technical dives with a buddy who was playing with a new computer. Our dives were planned using V-Planner, and we used bottom timers/watches for measuring devices. He had a new tech computer he wanted to play with, though, so he tried playing with the settings to see if he could come out reasonably close to what we had planned, and he wore it during the dive to see what would happen. Since he had no dives planned for a while after that, he did not care if it locked up.

As the dive progressed and we followed our ascent plan, the computer got increasingly cranky about our failure to follow its directions, even though our plan was really not all that different. During our 20 foot stop it got so angry it stopped advising us and went into error/gauge mode.

It got me wondering about something.

Are there any computers that have what I would call a reference mode or a backup mode? the idea of such a mode would be that the computer is a designated backup to the primary means of planning the dive. It could be the team wanted to use tables but liked the idea of having a computer backup, especially in case that unforeseen circumstances led to them having to deviate enough from their original plan that the tables they cut were too far off for comfort. It might be that the team is using computers but has designated one of the as the one to follow so that they can stay together on stops if the computer does not agree.

Maybe the only question I am really asking is if there are computers that won't lock up if you are not following them.
 
Maybe the only question I am really asking is if there are computers that won't lock up if you are not following them.
Are there any tables or plans out there that will continue to give you stop depths and times if you are not following them? In other words, if your dive plan for the ascent you have started says x minutes at 20', followed by Y minutes at 10', what does your plan tell you to do if you only do 1/2 of X minutes at 20'?

I assume that the computer continued to give you depth and time. There are many computers that, for the remainder of a dive, after you violate the ascent ceiling, will continue to give time and depth. After you violate the deco model, there really isn't any way to give recommendations for shallower stops.

The only way a computer could do what you ask for is for it to automatically change the deco model to one which is more and more aggressive each time you violate the original deco model.

There was a computer (Uwatec, I think) that had a microbubble model and it would indicate semi-optional deep stops. If you ignored them, it would recalculate using a less conservative model without the microbubble supression feature. It sounds like you are looking for something similar.
 
I assume that the computer continued to give you depth and time. There are many computers that, for the remainder of a dive, after you violate the ascent ceiling, will continue to give time and depth. After you violate the deco model, there really isn't any way to give recommendations for shallower stops.

The only way a computer could do what you ask for is for it to automatically change the deco model to one which is more and more aggressive each time you violate the original deco model.

I think that is what I am thinking of. I am thinking of something along the lines of my GPS. If I run into significant detours or if I decide to take a different route than the one it is giving me, that annoying voice says "recalculating" and gives me a new route. No matter how far I stray from the route I have been given, it keeps finding a new way to get me there.
 
What you are asking for is more like a GPS that somehow gets you home safely, after you have already driven off the cliff. :)

You exaggerate.

In the case I mentioned, we were following a V-Planner schedule absolutely perfectly. The guy who set it had tried to make all the adjustments to make it compatible. We were nowhere near a cliff when the computer gave up on us. I am looking for something that can make minor adjustments as team members make their stops and then not blow its top if they decide that they are just fine with the system they have given primacy and ended their last deco 3 minutes earlier than that computer thought they should.
 
I believe Cochrans won't lock you out. I dive/use Cochrans, but only as a recreational diver, so while they're technical computers, I don't ride 'em that hard and don't know from personal experience, but seem to have read that in several places.
 
I don't see how that would work either except not locking you out if by that you mean that it continues to work in gauge mode.

It's not like GPS in that with GPS anyway you get home is fine. With a deco model if it says that you have exceeded an M value for example how can it tell you how to reverse that? Once you bust a model how do you "unbust" it?
 
With a deco model if it says that you have exceeded an M value for example how can it tell you how to reverse that? Once you bust a model how do you "unbust" it?

It starts giving in-water-recompression stops? :D

boulderjohn:
You exaggerate.

In the case I mentioned, we were following a V-Planner schedule absolutely perfectly.
But once you have violated the computer deco model, as far it IT is concerned, you have dropped off the cliff.

That's why I said that the only way I can see for a computer to do what you want is for the computer to be more liberal (at each and every stop level ... not just overall) than your dive plan.
 
.....................Maybe the only question I am really asking is if there are computers that won't lock up if you are not following them.

My VR-3 (VRX better) will not lock out. I'm guessing, but I belive that it has to do with US law vs. English law.

Re-stated: My VR-3's will keep trying to get you back, no matter how stupid your dive profile.

Bottom line: If you don't like the outcome, go to England and look for sympathy.
 
My VR-3 (VRX better) will not lock out. I'm guessing, but I belive that it has to do with US law vs. English law.

Re-stated: My VR-3's will keep trying to get you back, no matter how stupid your dive profile.
Interesting. I took a look at the manual, http://www.vr3.co.uk/downloads/manuals/2007 VR computers manual.pdf

If you ascend beyond your deco stop for more than 60 seconds, the computer displays the directive "USE TABLE", but will continue to try and provide a best guess decompression algorithm. (By deco stop, I mean a real ascent ceiling, not a microbubble stop).

Based upon my playing around with VPM, this would mean greatly extended shallow stops, much longer than the original total ascent time.

Has this been your experience?

VR3 FAQ:
If you ignore or do not notice the DESCEND warning, after 60 seconds the “USE TABLES” message will appear. After this, the VR3 will continue to display decompression data but this will be “Best Guess” and cannot be relied upon. You should switch to manual back-up tables for the remainder of the dive.
http://www.vr3.co.uk/faq/faq.php#37
 
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