Computers and team deco ascents

[boulderjohn]

I have never used a computer to guide me through a deco ascent, but I know that some people do use a computer to guide the ascent, with tables as a backup. I don't wish for an argument on this topic--I just want some information.

If you and a teammate are going through your stops, and your computers are giving you different times at stop depths, how do you stay together?

 

[Dive-aholic]

I dive tables and use my computer as a back up. My tables are usually more conservative than my computer, so all is good. Most of the people I dive with do the same. I do have a buddy that dives a VR3 (I dive a Nitek He) and his computer gives him a stop at 60' every dive on one of our typical dives. I just stop and wait for him. It's no big deal and doesn't add any time to my decompression obligation.

As for doing a deeper trimix dive, that simply won't work. I teach my students to cut tables and make them follow the tables. I don't believe in flying a computer and won't dive with someone on those types of dives who dives that way.

 

[syntaxerrorsix]

We use our computers as a back up to the back up tables. We all dive Cochran 20H's with the conservatism closely based on the GAP RGBM software. Often on hot drops to our destination we may have a few seconds between splash, and have one or the other off by 30-60 seconds and we will simply put the last diver wet in charge of the time.

 

[DA Aquamaster]

I agree that proper dive planning is essential on a deep dive and on a deep trimix dive in particular. If a diver is simply flying the computer, the odds are good they never did a proper job of the gas planning.

With that in mind, whether you have real tables or cut custom tables on a PC or smart phone, the odds are that you are only approximating the actual profile so your tables and your computer are not going to exactly match, even if the computer is set up to produce the same profiel as your tables under identical conditions.

Then in the real world when you add team mates with different computers, different software, or even OC and CCR mied teams, the profiles start to diverge.

When the actual dive is such that you are shallower than planned for much of the dive (real world multi-level rather than square profile) and ythe computer shows a lot less deco than the tables I cut, I'll go with the computer, especially when the extra time and gas penalty would be imposed on the entire team. If there is no deco advantage, why use the extra gas?

On an ocean dive the deep stops are invariably pretty short, so the team separation is usually no more than 10 vertical feet anyway as the team moves up the line. Similarly, on the shallow stops even a difference of a few minutes won't mean a large separation, but the diver with the faster profile always has the option of just delaying the ascent to the next stop for a few minutes.

In a cave, that 10 vertical feet can be significant so the divers will want to follow the most conservative profile/computer in use.

In any case, during the planning phase the divers need to get together, compare computer, deco software and/or table profiles and agree upon a common plan or methodology for conducting the dive, so there should be zero confusion during the dive.

 

[Gareth]

I use ratio deco rather than a computer or tables. If I'm calling the deco the the only time we'd do something different to what I'm calling is if someone wanted to extend the deco for any reason, or disagreed with me, in case most conservative wins.

 

[boulderjohn]

I asked a similar question in reverse in a different thread. In it, I described the idea of diving tables with a computer backup, and I described a situation where my buddy and I were following a V-Planner schedule perfectly. He had a new trimix computer, and he wanted to experiment with it, essetially using it as a backup. He tried to put all settings to the degree that he thought it would display a compatible profile. We assumed that if it did not like the V-Planner schedule it would keep trying to find an acceptable schedule and finally give us an extended shallow stop. It did not. It went into gauge mode (Error) during our 20 foot stop, shutting him out, I assume, for two days. (I left the state shortly after that, so I am not perfectly sure.)

In that other thread, I am being told by some that you can't use trimix computers as backup for this reason.

Since some of you obviously do this, this opinion must be incorrect. I assume you are saying that with the computers you use, if you do not follow what it tells you to do, it will continue to give you a deco profile, resulting in the end in a difference in the final stop and not resulting in a lockout if you do not do the extra minutes. Is this correct?

 

[rjack321]

I asked a similar question in reverse in a different thread. In it, I described the idea of diving tables with a computer backup, and I described a situation where my buddy and I were following a V-Planner schedule perfectly. He had a new trimix computer, and he wanted to experiment with it, essetially using it as a backup. He tried to put all settings to the degree that he thought it would display a compatible profile. We assumed that if it did not like the V-Planner schedule it would keep trying to find an acceptable schedule and finally give us an extended shallow stop. It did not. It went into gauge mode (Error) during our 20 foot stop, shutting him out, I assume, for two days. (I left the state shortly after that, so I am not perfectly sure.)

In that other thread, I am being told by some that you can't use trimix computers as backup for this reason.

Since some of you obviously do this, this opinion must be incorrect. I assume you are saying that with the computers you use, if you do not follow what it tells you to do, it will continue to give you a deco profile, resulting in the end in a difference in the final stop and not resulting in a lockout if you do not do the extra minutes. Is this correct?

This typically happens when you violate a ceiling and don't go back down to finish the time. The previous posters are not violating a ceiling in their computers. They are following a V-planner/decoplanner (whatever) schedule unless/until the wrist computer calls for more time at a stop. Then they stay at that stop until the wrist computer is clear and then continue with whichever is calling for more time - wrist or table.

If you violate a ceiling on most wrist computers and don't go back down to finish that obligation they don't just recalculate a new schedule from there up. As you discovered, they lock you out. The Liquivision is a bit of an exception I've heard, it will recalculate missed stops and add more shallow time to compensate.

 

[DA Aquamaster]

In that other thread, I am being told by some that you can't use trimix computers as backup for this reason.

Since some of you obviously do this, this opinion must be incorrect. I assume you are saying that with the computers you use, if you do not follow what it tells you to do, it will continue to give you a deco profile, resulting in the end in a difference in the final stop and not resulting in a lockout if you do not do the extra minutes. Is this correct?

You can but you have to understand what is going on with both the computer and table profiles and then do one of two things...

1. Set the computer to be a bit more liberal than the table so it's curve is always ahead of the table, or

2. Monitor the computer and if needed, delay the ascent a minute or two until the computer clears. Works fine but shoots a run tme formatted deco plan to pieces in short order.

In some cases, number 1 works great if you set the computer to be fairly liberal to get you out of the water ASAP (but still with reasonable safety) if you have an emergency the weather kicks up, etc.

 

[boulderjohn]

2. Monitor the computer and if needed, delay the ascent a minute or two until the computer clears. Works fine but shoots a run tme formatted deco plan to pieces in short order.

Aren't you in that case using the computer as your primary deco planner, with the tables as backup?

 

[rongoodman]

I'm a new tech diver and expect to be doing dives in the normoxic trimix range this summer. I plan on using tables cut with V-Planner and a bottom timer as my primary tool, but my Liquivision runs V-Planner Live, so I would expect it to agree pretty closely with the tables I cut, time and depth being equal. A Shearwater running their new(upcoming?) implementation of VPM would probably be OK too, but I wouldn't expect a Suunto or VR3, running their own proprietary software, to be anything but peeved that I was ignoring them. Too many different assumptions between the models used in the computer and the software generating the tables.

(I just noticed that this response actually should be in the other thread that Boulderjohn referenced.)