Deep stops, Pyle stops, Gradient Factor

[BlueDevil]

Thanks for the reply and your suggestions Roak, but, as I said in my initial post I am aware that Pyle stops are outmoded (although many have dived them, myself included, quite successfully in the past). I use VPlanner, but not RGBM software, until I am convinced that RGBM has some benefit over VPM (I am not going to spend the extra money on RGBM unless it produces schedules that can be shown to be better than VPM). For rec diving I usually use the "NAUI method" (although I and many other divers were using this simple process before NAUI launched it - it is basically the same concept as Pyle but uses the surface as your ceiling rather than using your first shallow stop as the ceiling).

So my interest in the Pyle stop "formula" is a theoretical one for comparison purposes. I can readily generate Pyle stops using ZPlanner but I have noticed that there are often discrepancies between the stops it generates and those that I would calculate myself. Some of this would be due to "rounding off" by the software, but that doesn't seem to be the only reason. A while ago I saw a Pyle stop formula that differed to the one I was using and so I am wondering if my maths has let me down and I have got the formula wrong.

And of course, even if Pyle stops are an outdated means of generating deep stops we must keep in mind the significant contribution by Richard Pyle and his often quoted article which was largely responsible for bring the deep stops concept before the diving community.

Anyway, does someone out there with a mathematical mind have a formula for claculating the midpoint between you max depth and your first required shallow stop????

Thanks, BlueDevil

 

[Charlie99]

I am a bit of a mathematical dyslexic so I am wondering if someone can give me an equation for claculating Pyle stops. I have seen two different methods and I am not sure which (if either) is correct. So I am sure there are some maths gurus out there who can give me a definitive answer.

"Correct" is a relative term, particularly for an ad hoc procedure.

Pyle Deep Stop Article is one of the earlier articles. It gives Richard Pyles algorithm near the bottom of the article:

1) Calculate a decompression profile for the dive you wish to do, using whatever software you normally use.

2) Take the distance between the bottom portion of the dive (at the time you begin your ascent) and the first "required" decompression stop, and find the midpoint. You can use the ambient pressure midpoint if you want, but for most dives in the "technical" diving range, the linear distance midpoint will be close enough and is easier to calculate. This depth will be your first deep safety stop, and the stop should be about 2-3 minutes in duration.

3) Re-calculate the decompression profile by including the deep safety stop in the profile (most software will allow for multi-level profile calculations).

4) If the distance between your first deep safety stop and your first "required" stop is greater than 30 feet, then add a second deep safety stop at the midpoint between the first deep safety stop and the first required stop.

5) Repeat as necessary until there is less than 30 feet between your last deep safety stop and the first required safety stop.

.

An interesting tidbit is that Richard Pyle refers to a 1989 presentation by Yount on VPM as the first scientific study that Pyle saw that supported his empically developed procedure. Deep stops have been around for a lot longer than most people realize.

I doubt that a profile you make up on-the-fly will be accurate enough that one could tell after the fact whether you were diving an on-the-fly Pyle vs. VPM vs RGBM profile. While crude, the Pyle method of generating deep stops has the advantage of simplicity.

Charlie

 

[Charlie99]

Anyway, does someone out there with a mathematical mind have a formula for claculating the midpoint between you max depth and your first required shallow stop????

(max depth + stop depth)/2 is pretty simple, and is accurate to within an inch or two since water density doesn't vary that much. Even if density did vary dramatically, your depth gauge is reading pressure anyway, so you would still end up in the right spot. And even if your gauges were reading absolute pressure or absolute depth, you still end up in the right spot.

You shouldn't really be using max depth, though, to calculate Pyle stops. When diving a multilevel profile, IMO you should be using the average depth of the last 5 or 10 minutes rather than some max depth that you were at 40 minutes ago.

 

[BlueDevil]

(max depth + stop depth)/2 is pretty simple, and is accurate to within an inch or two since water density doesn't vary that much.

Thanks Charlie99!!. That is exactly what I was wanting. The formula you have given is the same as one of the ones I have, so that seems good confirmation that it is correct (and the other formula I've seen is wrong).

Cheers, Blue Devil

 

[BlueDevil]

Deep stops have been around for a lot longer than most people realize.

Quite true! I didn't realize until recently that Haldane was a deep stop advocate, but for some reason the deep stops got left out of his published tables.

I doubt that a profile you make up on-the-fly will be accurate enough that one could tell after the fact whether you were diving an on-the-fly Pyle vs. VPM vs RGBM profile. While crude, the Pyle method of generating deep stops has the advantage of simplicity.

Yeah. While current thinking is that VPM/RGBM has greater validity than Pyle stops or GF's there is no actual research that says one is better than the other at this stage. The VPM/RGBM theoretical basis sounds good and probably in the future there will be enough data to validate it in actual practice. As you say the Pyle method is crude but simple and may still have some applications. Later this year i will be doing some tropical wreck diving and being a fairly remote area probably won't have access to a computer/laptop/deco software. We won't be able to pre-cut tables and take them over with us because the variety of possible dive depths and times is endless for the dives we will be doing. So basically it will be a matter of using a Buhlmann based dive computer with our own deep stops worked out on the fly. We may use the Pyle method, but on the other hand the half max depth method puts your first stop somewhere not too far from those of VPM-B (give or take a bit, depending on dive time). This isn't an ideal approach to deco diving, and it is always better to pre-plan all your deco, but if circumstances are such that this can't be done then I am confident that we can devise a safe deep stop schedule for ourselves.

Cheers, BD

 

[neophytediver]

Since I'm waiting on my AI creditials to arrive (I finished YAY!!!!) I'll post this here to get everyone's opinion....

Am assisting with my first OW class and was tagged to teach Decompression and Tables. Currently NAUI is recommending that for any dive over 40ft. in depth you make a 1 minute stop at half your distance and then continue to 15ft. and make a 2 minute stop. The other way is to just do the standard 3 minute stop at 15ft. I threw both of these out at our OW students and then explained to them why neither my boss or I subscribe to the new thought for use with OW students. I want to see what everyone's opinion is on what I told them.

The local quarry where we actually do our OW dives is at most 45ft. (The information on their website is wrong. If anyone knows of any accessible spot in that hole in the ground that is over that depth, let me know because I've never seen it. http://www.rockdivers.com ) It seems to my boss and I both to be silly to make a 1 minute stop at 22.5 ft. and then stop at 15ft. Then there is the issue of dives less than 40ft. By definition all dives less that 40ft. in depth are to be considered 40ft. dives Our students immediately grasped the problem in this example.

I'm of the thought that deep stops are a good idea, but the current standards for them are a little screwy. I for one feel that a better guideline would be for dives over 60ft. in depth rather than 40ft.

Curious as to your thoughts on this issue. Any of you Instructors or AIs feel this way too?

 

[carlislere]

Hi, Neophytediver,
Keep in mind that the information you are giving your Scuba Diver students doesn't necessarily apply to just a 45 foot deep rock quarry. Granted the deep stop would not be warranted in your quarry, but these future divers could end up living and diving at other locales. I hope you still have your students do a 3 minute safety stop at the end of each training dive just to get them in the practice of it.
Be careful explaining a concept to a class, then telling them why you do not subscribe to it. All you do is confuse them. If you are explaining that the deep stop is not necessary in the quarry, but useful in other locations, that is fine. You don't want to explain a concept, then tell them that you do not agree with it and leave it at that.
Just curious, do you teach the RGBM tables or the NAUI dive tables?

 

[neophytediver]

Granted the deep stop would not be warranted in your quarry, but these future divers could end up living and diving at other locales. I hope you still have your students do a 3 minute safety stop at the end of each training dive just to get them in the practice of it.

I was certain to hammer that idea home. In a perfect world OW divers would stick to the recommended 60ft. limit, but I know that this world is far from perfect.

If you are explaining that the deep stop is not necessary in the quarry, but useful in other locations, that is fine.

Exactly what I did. We've invited several of them on one of our trips to PCB this summer and I used that as an example.

You don't want to explain a concept, then tell them that you do not agree with it and leave it at that.

Wouldn't dream of it. I'm fortunate in that where I work there is a Course Director and two Instructors on regular staff, and several of our voulnteers are Instructors, AIs, and DMs for several different agencies (PADI, SDI/TDI, etc.), so I am being exposed to many different teaching styles and philosphies. I'm taking everything I've learned (and am still learning) from them, considering it carefully, and then being very careful to present it to our students. Whether I agree with an idea or not, I always state the advantages and disadvantages behind my philosophy and never present them as an "end all, beat all" approach. I'm careful to state the official standard first, my idea second, and then reenforce the official standard.

Just curious, do you teach the RGBM tables or the NAUI dive tables?

Standard tables. Honestly don't have a copy of the RGBM table yet and have yet to even put my hands on one. But thanks for asking me about it, it's one thing I'll have to remember to present to our students this Sunday. The way I teach tables I have the standard NAUI air tables and the NAUI Dive Calculator to teach from/with, but I also have copies of PADI's table, the USN tables, and NOAA's tables just so they can see the differences between them.

 

[simbrooks]

We briefly went over the safety stops on our instruction, but didnt do them during our checkout dives, due to the instructor anchoring the flag in the lake over a point 20ft deep, swimming out to a deeper point (36ft) and back again we didnt practice safety stops. It would have been more beneficial to anchor the flag for at least one dive at a deeper point to practice this skill, but it was a "fast paced" course, so what could we expect???

Since then we spent a weekend in the springs and managed to do stops with the visual reference of the side at 15ft, but when we did our first ocean drift dive stop we were clueless and all over the place - trying to read our guages to stay around 10-20ft, but yoyo-ing wildly. Since then we have tried to improve on that. So i think the lack of emphasis on making a stop in midwater during OW classes didnt help with our dives immeadiately after our certification. It wont hurt you or your students to do the stops, just for practice at doing them, what is it going to cost you, 1 min of time (replacing one at 15ft) and a fraction more air than the 15ft stop, and the benefit is that your students will understand that they should plan this into their dives. As said before, the instruction and subsequent denial of use of a this deep stop concept that you are teaching is not going to help the students either - they might be confused about the whole concept after the course. Working on skills and hovering at whatever depth is not a bad thing to learn, even if that half depth and the safety stop are only 7-10ft apart.

 

[sharkmasterbc]

Correct me if I'm wrong here but I was under the impression that deep stops are for decompression diving where you actually have a "soft ceiling". I realize that every dive is technically a "deco" dive because as soon as we begin our ascent we are decompressing.
At the OW level all dives are taught as "non stop" or "no decompression" dives arn't they? This means that you could theoretically ascend directly to the surface at any point in the dive providing you have a nice slow ascent rate ???
Although the idea of deep stops has been around for ages, the term kind of implies that you are diving deep...45fsw is not really considered deep, or is it ???. I would think that this concept would be more apropriate to teach at the advanced level where you would be diving to depths below 80 and above 100.
On a multilevel dive profile I have always divided my max depth in half and used that depth as the second level for the dive, so I guess you could consider that a "deep stop" but there would be a point where my fast tissue compartments would begin to ongass again if I stayed at that depth for too long thus making the "deep stop" usless right ?
Please feel free to enlighten me if I'm missing something...