Wisdom Computers and new Rule of Halves

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FritzCat66

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NAUI is now changing their training, based on current research, to include a 3-minute safety stop at half the max. depth for recreational non-deco dives below 40', and then just a one-minute shallow stop at the traditional depth of 15'-20'. This jives with a lot of the research I've seen for reducing microbubbles, and I expect many if not all the other agencies will be following suit.

I really like the safety stop countdown timer on my Wisdom 2. It would be great if the timer would calculate the half-stop depth and kick in a countdown timer for that, and modify the shallower stop time to 1 minute as well (for dives below 40' of course). Is there any word on whether Sherwood will be releasing an update to the Wisdom to accommodate the new Rule of Halves safety stop protocol?

If so, would such a programming update be downloadable/installable by us users, or would it likely be something we would have to take it in to our Sherwood dealers for (or send back to Sherwood)?

Meanwhile, of course I can follow the new rule "manually" by calculating my own half-stop depth based on the max depth display on the Wisdom, and watching my dive time clock, then of course doing the shallow stop and ignoring the countdown timer by surfacing when it says 2 minutes left (i.e. one minute complete). But with just a little reprogramming, it would be great if the computer could do all that for me.

So, what's the official word on this from Sherwood? Is this in the works at all? Are they waiting for the other agencies to follow suit first?

>*< Fritz
 
My recommendation is to do what I do - calculate and execute the half-deep stop manually, then complete the 15' stop for three minutes as your computer wants you to do. Most people believe that the three minute stop should be for "at least" three minutes.
If you do both the half-deep and a three minute at 15', you'll be safer. Don't be in a rush. And remember to ascend extra slowly the last few feet because that is where the pressure changes the most rapidly. The shallower you are, the more slowly you should ascend.
 
NAUI is now changing their training, based on current research, to include a 3-minute safety stop at half the max. depth for recreational non-deco dives below 40', and then just a one-minute shallow stop at the traditional depth of 15'-20'. This jives with a lot of the research I've seen for reducing microbubbles, and I expect many if not all the other agencies will be following suit.
You are leaving some details out I hope.

Lets say I go down to 130' for 5 minutes on a wall, then on up to 100' for 5 then on up to 70' for 15 minutes. Is my ascent from that point really supposed to be 3 minutes at 65' and then just 1 minute at 15-20' ??
 
Whatever the new training plan is.....I can tell you that Sherwood (or their manufacturer) will not likely change computer routines to match. It just simply isn't that easy.

Phil Ellis
 
You are leaving some details out I hope.

Lets say I go down to 130' for 5 minutes on a wall, then on up to 100' for 5 then on up to 70' for 15 minutes. Is my ascent from that point really supposed to be 3 minutes at 65' and then just 1 minute at 15-20' ??

YES!

As long as you are staying out of deco range, and within rec depths (your 130' is max. there), then yes, that's exactly what the new recommendations would have you do. And it's based on good science.


My recommendation is to do what I do - calculate and execute the half-deep stop manually, then complete the 15' stop for three minutes as your computer wants you to do. Most people believe that the three minute stop should be for "at least" three minutes.

Yes, that's what people have believed, but the research isn't backing that up. In fact, the latest change to the NAUI standard reduces the shallow stop from three minutes to one minute, again for good reason - it reduces overall microbubble formation.

Here is the latest bulletin I know of on this matter from NAUI (bold emphasis mine). Again, having kept up with the research results, I think it's inevitable that the other agencies will follow suit. I'm just hoping my computer will as well.

>*< Fritz


Rule of Halves Revised

Based upon the most current research and analysis of decompression science on the value of deep stops in &#8220;no-required-decompression&#8221; diving by Bennett et al (Undersea and Hyperbaric Medicine 2007; 34(6): 399-406, the NAUI Board of Directors approved a change to the NAUI Standards and Policies on March 7, 2008, at its annual meeting. A reprint of the study is included in this issue of Sources (pp. 48 ff).

The membership is advised to make a pen and ink change in their personal copy of the manual and mark both the title page and changed page with &#8220;rev. 1-08.&#8221; Notice of these changes is included in existing inventory of the NAUI Standards and Policies Manual, and the changes will be incorporated in the next printing.

S&P Page 2.16 &#8211; Current wording
It is recommended that following dives in excess of 40 feet (12m), divers make a one minute stop at a depth that is half that of the deepest depth reached during the dive and make a precautionary stop in the 10-20 feet (3-6m) zone for three to five minutes before returning to the surface. The precautionary stop time may be considered &#8220;neutral&#8221; time- not counted as either dive time or surface interval time.

S&P Page 2.16 &#8211; Changed wording
It is recommended that following dives in excess of 40 feet (12m), divers make a two to three minute stop (with two and one-half minutes being optimum) at a depth that is half that of the deepest depth reached during the dive and make a precautionary stop in the 10-20 feet (3-6m) zone for one minute before returning to the surface. The precautionary stop time may be considered &#8220;neutral&#8221; time - not counted as either dive time or surface interval time.

Bennett et al have extended their study to include diving over a greater range of depths from deep (130 fsw) to shallow and will present these findings at the UHMS &#8220;Decompression and Deep Stop Workshop&#8221; on June 24-25, 2008, in Salt Lake City, Utah, sponsored by NAUI Worldwide and other dive industry members.
 
Whatever the new training plan is.....I can tell you that Sherwood (or their manufacturer) will not likely change computer routines to match. It just simply isn't that easy.

Well, having been a programmer before, I can say it's certainly not difficult from a programming perspective. I mean, they coded in that handy three-minute 20' stop timer... why? Because until recently, that was the standard recommendation. The recommendations are now changing, so they should update the code.

I suspect the reasons for not updating the code are more on the non-technical side, e.g. legal liabilities, access to source code (I know Sherwood is not the OEM for the Wisdom, and even the OEM may have contracted out the programming), logistics, things like that.

Anyway, I'm not expecting new code for my computer tomorrow, even though I am diving the new recommendations already. I would just like to know if Sherwood is looking at the issue, or bring it up if they aren't.

>*< Fritz
 
YES!

As long as you are staying out of deco range, and within rec depths (your 130' is max. there), then yes, that's exactly what the new recommendations would have you do. And it's based on good science.
Actually, it's a grossly oversimplied approach which is incorrect in many circumstances. Thank you for providing the actual wording of the new NAUI recommendations. I find them surprising.

Here's a very simple mental exercise that should show clearly that the deep stop should be based upon the average depth over the previous 15 minutes or so, rather than being based upon the maximum depth.

Imagine a profile where one briefly descends to 130', then ascends to 65' and stays there until reaching NDL. Taken literally (which is what a computer would do if it implemented the rule as written), the NAUI half-depth rule would have you then extend your stay at 65' for another 3 minutes beyond NDL, and then ascend directly to 15' for 1 minute only. Hopefully, you wil agree that this profile is far, far from optimum.
 
Imagine a profile where one briefly descends to 130', then ascends to 65' and stays there until reaching NDL. Taken literally (which is what a computer would do if it implemented the rule as written), the NAUI half-depth rule would have you then extend your stay at 65' for another 3 minutes beyond NDL, and then ascend directly to 15' for 1 minute only. Hopefully, you wil agree that this profile is far, far from optimum.

I partially disagree - I do agree that the better halfdepth stop in this case would be something shallower than 65', but as far as the time is concerned: the computer should have already factored in the 3-minute halfdepth stop time as well as the 1-minute shallow stop time as part of the NDL that it was displaying (the safe time remaining on the Wisdom display). Thus, if the diver were following their computer, they wouldn't be extending into NDL at all with that profile.

I know the Wisdom as-is right now factors in the 3-minute shallow stop as part of its safe time remaining calculations.

>*< Fritz
 
I know the Wisdom as-is right now factors in the 3-minute shallow stop as part of its safe time remaining calculations.
Huh??? At the 15-20' stop, any compartment near its limits will be offgassing and the very slow compartments that might be ongassing will never reach their limits (the min bends depth for the DSAT model used in the Pelagic Pressure Systems computers such as the Wisdom is about 23').

This means that the 3 minute shallow stop has no effect on NDL at ANY depth or profile. So there is no need to "factor in the 3-minute shallow stop as part of its safe time remaining calculations."" nor is there any possible way to do so.
 
I know the Wisdom as-is right now factors in the 3-minute shallow stop as part of its safe time remaining calculations.

I know the Wisdom also let you pick the tank pressure at the end of the dive and uses that to calculate safe minutes remaining! Hardly optimal gas planning if you call it gas planning at all.

The point is to not disengage the dive computer between your ears and "fly" your - in this case - console blindly. Some days are different than others and you should take that into account when you decide on a profile. I can promise you that your Wisdom doesn't.

Charlie99 gave you a perfect example. Forget for a minute what NAUI says and think about it...

Later,

Willem
 

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