Rule of Halves?

[Charlie99]

A good paper on deep stops by Erik Baker can be found multiple places on the web, including http://www.gap-software.com/pdf/deepstop.pdf .

This explains the gradient factor method of generating deep stops. You can select gradient factors in many deco programs, such as GAP and Decoplanner.

An interesting story of how Richard Pyle re-discovered deep stops can be found at http://www.bishopmuseum.org/research/treks/palautz97/deepstops.html . Much more readable than the Erik Baker article.

The NAUI stops are similar to the ad hoc method publicized by Richard Pyle, but the Erik Baker method is better grounded in physics and are preferred by most divers -- probably including Richard Pyle.

Charlie

 

[jbd]

provided in the links Charlie99 posted.

Also, I would like to point out that this is NOT a new standard for NAUI. It is provided as an alternate method of doing a safety stop which allows the diver to take advantage of the benefits of using deep stops as pointed out in the articles Charlie99 referred to.

 

[ktarlecky]

I learned the rules of halves in my YMCA open water class two years ago. I only use the "half stop" rule when I dive 50 feet or deeper. Any shallower than that I stop for 5 minutes at 15 feet. the rule of halves has become a diving habit. Just make sure your buddy is on the same page and understands the plan.

 

[Diver0001]

double125's once bubbled...
Here is something I do that I would like the experts to comment on. It is along the same lines as the rule of halves and I think it may be benificial in this thread. I due a one minute stop at half the depth but from there I slowly ascend ten foot then I stop for the remainder of that minute, then I ascend ten foot and stop for the ramainder of that minute. I continue that till I reach my safety stop and due a minimum of 3 minutes there. This helps me keep my ascents slow and I feel it has been benificial to me. Any comments? Is this good/bad?

This ascent looks good. I plugged it into gap for maxed out 40metre and 20metre profiles to be sure and it works for both of those.

In general you should be aware that, especially on a deep dive, you can continue "ongassing" as you ascend if you ascend too slowly. SeaJay recently posted an experience he had with ascending too slowly and what he thought was a safe ascent actually became an unplanned deco dive. His ascent was a lot slower than the one you're describing, though.

Cheers,
R..

 

[Charlie99]

Diver0001 once bubbled...
In general you should be aware that, especially on a deep dive, you can continue "ongassing" as you ascend if you ascend too slowly.

Not only "can you continue ongassing", you definitely will. You will definitely be ongassing the very slow compartments, at least until you are shallower than 22' on air*. The reason computers "penalize" you for deep stops is because you ARE ongassing, at least in the slow tissues. The deep stops, however, are offgassing the fast tissues.

Skip the deep stops and you run the fast tissues closer to their limits and promote bubbling. Extend the deep stops too long and you have further loaded up your medium and slow tissues and either have cut your safety margins or have extended your shallow stops.

The Erik Baker articles show one method of achieving this balance. The VPM programs are another. Results are similar.

Charlie


*math behind my claim that you are always ongassing when deeper than 22' on air:

M0 for ZHL16A/B/C 635 minute compartment is 41.8fsw. Divide by 0.79 (fraction N2) to get air depth of 52.9fsw (absolute), or 19.9' depth below surface. Add in the H20 vapor pressure of 1.6-2' and you see that at approx 22' you will be ongassing into the 635 minute tissue as long as it is below M0 level.
If your 635 minute tissue is into deco, you ain't doing rec diving or anything even close.

** If you run the PADI tables to their absolute extreme limits repeatedly, you will see that your average depth (including SI) is about 22-1/2'. Not a coincidence.

 

[Uncle Pug]

jonnythan once bubbled...
the rule of halves is thus: After subtracting your rock bottom gas....

...that the term "Rule of Halves" was used to describe NAUI's *new* method of adding in deeper stops.

Since the Rule of Halves and the Rule of Thirds are about gas management it is possible that NAUI was unaware of them.

 

[plsdiver4377]

If I remember correctly the rule of halves is mentioned in the NAUI OW and the rule of thirds is mentioned briefly in the AOW open water as gas management tool for technical diving. It was definitely not on the tests that I had to take.

My instructor however covered both in detail. Therefor I was a little confused the first time I saw it as an ascent/stop method. He covered half depth stops as well just didn't call it the rule of halves.

 

[Uncle Pug]

plsdiver4377 once bubbled...
He covered half depth stops as well just didn't call it the rule of halves.

Is it possible that NAUI isn't calling their new half depth stop the rule of halves and that is just what Curly and Netdoc called it here on SB?

 

[plsdiver4377]

Uncle Pug once bubbled...

Is it possible that NAUI isn't calling their new half depth stop the rule of halves and that is just what Curly and Netdoc called it here on SB?

it is entirely possible since I just looked it up in the books (last years) for both classes and I didn't see it (except as gas management). I found the notes I took (what our instructor told us) about it on the side of the page regarding safety stops.

 

[jbd]

the name NetDoc and Curly are using. Thats the name used in the magazine that NAUI sends to its members.