Diving with computer in gauge mode

[Mr Carcharodon]

In any case, while reading the document is all fine and dandy, I'd recommend attending one of the Ratio Deco lectures Andrew Georgitsis teaches before applying it in the real world (not that anyone has suggested otherwise).

Of course one of questions Andrew asked in the class was how my depth averaging was going. So there is at least some expectation that you will be trying parts of the method going in. But then trying and applying may be different things.

 

[Blackwood]

^^ Aye. It's a good thing to practice. Even if you aren't using it to figure deco, it forces you into a state of acute awareness about your profile.

 

[monster]

I think I should actually title this the lost art of diving without a computer

When I started diving I got a computer and my instructor said to put the tables away and just use the computer, hence I did. I understand the tables but they are for square profiles however the majority of my dives are anything but square.
/QUOTE]

PADI has two approaches: the eRDP ML (an electronic calculator with multi-level capabilities) and The Wheel, a rotating dive table that takes multi-level diving into account.

The problem with either approach is that it is most useful AFTER the dive unless you know EXACTLY what the next dive will look like. I have never known in advance what a dive will look like so neither appeal to me.

So, you have two real choices: use the tables and a square profile or use a computer. The nice thing about tables with multi-level diving is that you almost never push the NDL whereas with a computer, the Remaining Dive Time is, by definition, right at the edge. True, you can finish before the time is up or add a factor to make the computer more conservative but, basically, RDT is a lot closer to the edge than you would ever get with a square profile on a multi-level dive.

For a number of reasons (primarily obsolete gear), I have ordered a computer. I plan to use it in gauge mode for quite a while specifically to force our little group to use tables. After all, the PADI Nitrox course is totally about the tables. How odd that they dropped tables from OW in favor of the eRDP and then turn around and expect competency for the Nitrox course.

Richard

You can actually use square-profile tables (assuming you don't have a multi-level planner like the wheel) to plan multi-level dives; just plan the succeeding levels as repetitive dives with zero SIT.

Richard raises a good point about not knowing what the dive will look like before doing the dive, but if you know the sites and what you're looking for, or if you can get that information, then you can make a reasonable approximation of the dive profile and use that to plan your dive.

While planning the levels, you can also do backup/alternate plans (say +/- 5 or 10 minutes per level, or adjustments on level, i.e., same time but +5 ft.), just to give you an idea of how you can revise your plan as you go and still stay within NDLs.

And then, whether you do the alternate profiles or not, what the computer can do is give you real-time information as you hit the levels, and you can adjust, for example, if you want to spend a little more time at that level, because you've come across something interesting.

When my students start diving with computers, I don't tell them to put away the tables, I encourage them to still plan on tables (and gather all the site information they'll need), and then use the computer as a tool to help maximize the dive.

 

[Supershark]

Hi all
Just a quick note. Had a chance to play around with the ERDPML today, works well, however it is electronic, as we all know water and electric stuff doesn't mix well. I will continue to teach my students the tables/wheel as well as the erdpml, ok more work for me, but i hope better equipped divers going out into the world!

 

[String]

One thing that is worth practicing that lots of people struggle with are planning a dive on tables (depth and time) and hitting those times exactly along with precise ascent rates and stop times.

Leave the computer in computer mode but plan a dive say spending 12 mins at a certain depth then ascend to xx depth at xx rate for a simulated stop and so on.

It does take some getting used to if you havent done it before.

 

[DwayneJ]

The nice thing about tables with multi-level diving is that you almost never push the NDL whereas with a computer, the Remaining Dive Time is, by definition, right at the edge. True, you can finish before the time is up or add a factor to make the computer more conservative but, basically, RDT is a lot closer to the edge than you would ever get with a square profile on a multi-level dive.

Richard

Just to clarify, with air integrated computers, remaining dive time could be your nitrogen loading, your air (with a programable reserve figure), or your oxygen loading (while diving nitrox).

On air dives, my remaining dive time is normally my remaining air supply.

IMHO - Computers can save you from some really sticky situations. Conditions, currents, gear failure can abruptly change your dive profile and without a computer you would need to recalculate your profile on the fly or more than likely thumb the dive. Worst case would be getting into a situation which required deco obligations.

 

[Blackwood]

Worst case would be getting into a situation which [-]required deco obligations[/-] you don't have enough gas to safely get yourself out of.

fixed

 

[TSandM]

I've had the interesting experience, over the last three weeks, of diving unfamiliar sites and profiles with a computer which is NOT in gauge mode. (I'm demoing a Liquivision computer, and was requested to allow the VPM software to run, so I have.)

I have used a depth averaging approach, along with being mindful of Steve Lewis's "The Shape of the Curve" article, and a former SB post of Uncle Pug's about spending as much time above 30 feet as you do below 60 (it's been removed, so don't bother looking for it). The UP approach leaves one a little bit in limbo about the part of the dive between 60 and 30, but what I noted with the VPM software was that, even if I was really pushing NDLs at depth, once I got to 40 feet, my times expanded tremendously. (Even at 50, they had become very comfortably larger.)

So, I guess what I have taken away from watching the computer is that you can do a multi-level dive pretty easily in a way that would satisfy VPM (or Suunto's RGBM, which tracks very similarly, at least as far as my husband and I found on our trip). You do have to decide how much depth averaging you're willing to do in the deep section, and weight it according to the profile, but if you then shape the ascent curve and spend enough time shallow, you will at least have satisfied those two types of software (and done a dive which follows the exponential deco curve, with some "deep stop" equivalent time as you transit the 40/50 foot range. )

Mind you, I'm not RECOMMENDING this (as UP didn't in his article, either). I'm just saying that that's what I do, and it kept the VPM software happy through this trip.

 

[Blackwood]

Adding to TSandM's post, here's a comparison I put together of various decompression curves for the same time/depth/gas combination.

I find it interesting to see how the different algorithms stack up.

Notes:
1) I had to forcefeed a longer dive into vplanner since it counts the descent towards bottom time whereas decoplanner and ratio do not.
2) I've hidden the depths, runtimes, and gases so as to not encourage anyone to try to follow the profiles (not that anyone familiar with this stuff can't figure it out anyway). Suffice it so say it's a generic tech 1 level one bottle dive.

 

[Charlie99]

I've had the interesting experience, over the last three weeks, of diving unfamiliar sites and profiles with a computer which is NOT in gauge mode. ......I have used a depth averaging approach,

I've seen various people post that they needed to dumb down their computer to work as just a bottom timer because the computer calculated NDLs distracted or confused them as they were doing their own mental depth averaging / NDL calculations / deco calculations.

Did you find running the computer as a computer distracting? Helpful ? OK for you, since you were already practiced in depth averaging, but might be a problem for someone just learning to track their own deco status mentally?

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Did the two methods interfere with each other on repetitive dive calculations?


Charlie Allen