Diving with computer in gauge mode

TheWetRookie · Oct 10, 2008

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

I am looking at taking tech courses next year but until then I want to get used to diving with the computer in guage mode within recreational limits.

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.

My dives are usually wall dives that start deep and work up into the shallows. (A nice long ascending slope)

Any sugguestions or direction on how I should be planning such a dive these?

Would it be just a case of do not exceed NDL at depth and then work my way into the shallows and not worry about how much time is spent in the shallows since I would most like run out of air before hitting the shallow NDLs?

Please and thanks

CoralSeaMan · Oct 10, 2008

If you do not want to use a computer (?) you need to use something that PADI calls multi-level diving. I assume other agencies have something similar. The idea is to dive in steps (eg. 100 ft., 70 ft., 50 ft., 40 ft.) and essentially recalculate your profile at each level. Since your computer is doing such calculations constantly, why not just use your computer.

Tortuga68 · Oct 11, 2008

My computer (suunto vyper) doesn't do multi-gas, so any time I do tech dives, I switch it to gauge mode. No problem, except for the no-dive limit/getting locked in gauge mode until they pass

When using gauge mode, I plan the deco and have the deco stops on my slate by time/depth, plus overtime stops

If you're doing rec (non-deco) diving, you won't need to do this, so I'm not sure if there is much point to what you propose? Other than getting used to using tables again/for the first time - but it's really not that hard; bigger concern is dealing with it when narked

Your tech course should start with introducing you to the concepts anyway - suggest you do EAN intro first, then goto advanced nitrox and deco procedures

Maybe a better idea would be to practice using an SMB? It's more of an art than following a table

My $0.02

rstofer · Oct 11, 2008

TheWetRookie:
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

HowardE · Oct 11, 2008

The art of diving without a computer isn't a lost art... but it's just not practical for multi-level dives.

The problem with using tables, as stated is that the tables assume square profiles.

If you take deco training... you will plan dives using a dive table.

My advice is... don't bother practicing using Gauge Mode. It's just a depth gauge and bottom timer. Why would you need the practice?

Depending on which agency's Deco Procedures you take... you'll may or may not learn gas switches in your training anyway, and your computer will most likely work fine, and you may even find that your computer assigns you LESS deco than you'll have calculated in your dive plan.

If you're currently diving your computer... then dive your computer. If you don't know how to use the tables... then review them when you begin your deco training (hopefully your instructor does that anyway).

Charlie99 · Oct 11, 2008

What are you trying to accomplish by dumbing down your computer?

Review http://www.txfreak.de/ratiodeco.pdf but it would be best to keep your computer in computer mode as a crosscheck while you gain practice in the "depth averaging" method.

Also review http://dir-diver.com/en/knowledge/average_depth.html. That article has some good info on when depth averaging is valid and when it underestimates the deco required.

Mr Carcharodon · Oct 13, 2008

The question you have to answer is how to calculate your NDL from the depth and time readings you get in gauge mode. Ratio deco uses an average depth and some rules of thumb to arrive at a NDL or a deco schedule. There are some built in assumptions about the shape of your depth v. time profile and about the details of the ascent. So the usual advice is not to do this without training. But you can practice depth averaging and using ratio deco and compare it to what your computer is telling you. You may find that your computer sometimes gives unreasonably short NDLs based on incorrect assumptions about what the rest of the dive will look like. Also I would suggest getting a deco program (e.g. v-planner) and compare the results you get with ratio deco to the program.

Here’s a useful link:
Team foxturd: Tech1 Ratio Deco - Explained

Blackwood · Oct 13, 2008

Mr Carcharodon:
Here’s a useful link:
Team foxturd: Tech1 Ratio Deco - Explained

It's important to note that he's explaining Trimix + Deco-gas Ratio Deco (tech 1 +), whereas for the time being, the OP would likely be using the MDL table if anything.

The curve is very different for backgas decompression.

With deco gases (like 50%), Ratio Deco calls for an s-curve to take advantage of the oxygen window (which the author of that page you linked makes reference to under the heading Shaping the Decompression Curve - Intermediate Stops).

Backgas decompression via the Ratio Deco/GUE MDL table should be exponential since you're relying on the gradient alone.

Also, unlike the tech 1 Ratio Deco explained in that link, adding an O₂ bottle does accelerate MDL deco.

Just food for thought.

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).

TheWetRookie · Oct 13, 2008

Hmm, food for thought and some good reading. The shop where I will be taking my tech courses teaches ratio deco so I have done some reading on it already. For now I want to stay within recreational limits. I think I will just leave the computer in computer mode until I start with the classes.

Thanks all.

Blackwood · Oct 13, 2008

TheWetRookie:
For now I want to stay within recreational limits. I think I will just leave the computer in computer mode until I start with the classes.

While extended deco on the MDL table has some finicky rules (like adding the min-deco ascent to anything less than 20 minutes of extended deco), using the MDL table and diving with the computer in gauge mode seems like a fine option to me so long as you remain within MDL limits. So long as you stay within the stated limits, do the stated ascents, and adhere to the stated surface interval, it's merely a different table.

Diving with computer in gauge mode

Please register or login

TheWetRookie

Contributor

CoralSeaMan

ScubaBoard Supporter

Tortuga68

Contributor

rstofer

Contributor

HowardE

Diver

Charlie99

Contributor

Mr Carcharodon

Contributor

Blackwood

Contributor

TheWetRookie

Contributor

Blackwood

Contributor

Similar threads