Padi Advanced OW - Deep stops??

[RyanT]

just to reiterate what both tbone and I said... Yes, the perdix is a technical computer, but put it in recreational mode and you've got one of the simplest to use and easiest to read computers around.

 

[tursiops]

As the AOW course is still a recreational course, all dives are within NDL so only the safety stop is mentioned and even then it is an advisory stop not a mandatory stop.

If you exceed NDL, then you enter into the requirement for mandatory stops

Well, the RDP says the safety stop is "required" for all dives to 100 ft (or more), and also for any dives within three pressure groups of the NDL, no matter the depth. So even a dive to 70 ft (to meet the AOW Deep Adventure Dive requirement) will require a safety stop for a 49-minute (or more) BT. Yes, I understand "required" is not the same as "mandatory," but for teaching purposes in AOW you do the safety stop.

 

[Neilwood]

Well, the RDP says the safety stop is "required" for all dives to 100 ft (or more), and also for any dives within three pressure groups of the NDL, no matter the depth. So even a dive to 70 ft (to meet the AOW Deep Adventure Dive requirement) will require a safety stop for a 49-minute (or more) BT. Yes, I understand "required" is not the same as "mandatory," but for teaching purposes in AOW you do the safety stop.

I would agree that, for instructional purposes, the safety stop must be taught. Is it good practise? Definitely yes.

What I was alluding to is that by staying within NDL the safety stop is just that - a stop to add an additional safety (conservatism) to the dive profile. It is not a deco stop as such.

Having said that, I will always do my safety stop - for the time involved, I would rather be that bit more conservative.

 

[dmaziuk]

In AOW, I thought the recommendation was to do a 1 minute stop at half the deepest depth. Eg if you first went to 30m then you stop for 1 min at 15m somewhere during the total dive time. However, you can just swim along at 15m for 1 min.
I then do 3 mins at 6m, 1 min at 3 metres and surface.

Personally I believe in magic powers of sqrt(2). So coming up from 4 atm I'd make a stop at 4/1.414 = 2.8 atm = 18m. 2.8/1.414 = 2 atm = stop at 10m. That divided by 1.414 is the safety stop at 4 m and after that I'd have to surface before the whole thing turns into Achilles vs the turtle. I am convinced that my ascent profile will result in lower BSIndex numbers than either half-depth or half-pressure stop schedule. (Disclaimer: BSIndex is a poor predictor for DCS and its relationship to off-gassing of fast tissues is... well... "we hope it exists".)

 

[Nikole]

Guys I've been looking at the Mares Icon HD computer... Looks pretty cool. Still above my progress credit range... I would actually look into getting that or the shearwater if I wasn't still paying student loans

 

[EFX]

I'm (still) shopping around for wrist computers and would like to know, in the Padi advanced open water course, during your deep dives, did you ever do a deep stop or anything? That way rule in, or rule out choosing a dive computer with that feature.

I would not rule in or out a computer that calls for deep stops based on the courses you take at the recreational level. Before I got my Shearwater Perdix I used a Mares Puck which incorporated the RGBM (Reduced Gradient Bubble Model) algorithm. There have only been a handful of (recreational) dives where it called for a deep stop (fixed at one minute). On those dives I was within 5 minutes of NDL. I didn't have it for my AOW deep specialty but as I recall we weren't at depth long enough to require a deep stop. Other computers may be more conservative but my guess is you won't be at depth long enough for a deep stop. However, if you get a computer that uses deep stops, discuss this with your instructor including how you will signal if you must make a deep stop. If you need to stop (highly unlikely) a DM should stay with you until you complete the stop. The instructor and the rest of the group can proceed to the SS.

 

[rjack321]

In AOW, I thought the recommendation was to do a 1 minute stop at half the deepest depth. Eg if you first went to 30m then you stop for 1 min at 15m somewhere during the total dive time. However, you can just swim along at 15m for 1 min.
I then do 3 mins at 6m, 1 min at 3 metres and surface.

Only NAUI teaches this officially.
As a practical matter 1 minute a little deeper than a typical safety stop depth isn't very important one way or the other. Some data suggests it might help and some data says its counterproductive. Not a settled topic but no computer actually specifies a stop that deep anyway.

 

[Basking Ridge Diver]

Not a settled topic but no computer actually specifies a stop that deep anyway.

Oceanic Veo 2.0 has a deep stop - equal to half the max depth. User can turn it on or off - no penalty for skipping it if it is turned on.

 

[Diver0001]

In AOW, I thought the recommendation was to do a 1 minute stop at half the deepest depth. Eg if you first went to 30m then you stop for 1 min at 15m somewhere during the total dive time. However, you can just swim along at 15m for 1 min.
I then do 3 mins at 6m, 1 min at 3 metres and surface.

Ok, This is how it really works for those of you who are still confused about what PADI actually teaches.

1) If you are using a computer then PADI tells you to read the manual and follow the suggested operating procedures.
2) If you are using a table then PADI tells you to read the manual and follow the suggested operating procedures.

The most common table you might encounter during a PADI course are the PADI tables. The PADI tables contain no standard procedure for deep stops.

If the course is being given with a computer and the computer suggests a deep stop then the instructor will probably follow that. PADI instructors are neither required to insert deep stops nor required to ignore them.

The confusion here is about the recommendation to do a 1 minute stop at 1/2 maximum depth. This is a NAUI procedure. It may have been picked up by a PADI instructor but it is not a PADI procedure. PADI will allow a discussion about it if the instructor sees fit as long as the instructor is still executing a no-stop dive. There is, however, no mention of such a procedure in the theory that I'm aware of.

The big picture here is that PADI is very conservative when it comes to changing its procedures. When they do so it is done based upon solid scientific testing. In the case of deep stops there was no solid scientific testing. It was a rule of thumb that some technical divers built into their ascent procedures based upon anecdotal evidence that it seemed to work for some divers.

NAUI picked it up and decided to make it a standard operating procedure in order to keep up with the times. When they did so it was assumed that this was a valid strategy and given the popularity of deep stops at the time it was a defacto "best practice". I'm sure NAUI thought they were just implementing something that was obviously a good thing.

Subsequent scientific testing has shown that bubble models like RGBM and the Thalmann model that NEDU tested are biased to over-saturate slow tissues during ascents from decompression dives. Since these models create very deep ascent lines that they call "deep stops", some divers have started to question the utility of deep stops altogether. This is, however, a point of confusion about vocabulary because the term "deep stop" is being used in two different ways.

In fact, what the NEDU study shows isn't that deep stops are bad. It shows that if you make a deep stop you need to extend your shallow stops, not shorten them, as algorithms such as RGBM does. For technical divers this basically killed RGBM but we already knew it was broken from about 2005 onwards anyway, so nothing has changed.

So where does this leave a recreational diver who learns about deep stops? The short story is to go ahead and do them. BUT if you are using a table, count the deep stops as part of your bottom time for planning. If you are using a computer, the computer will recalculate your NDL as you go, so you can make as many stops as you want during ascent and the computer will automatically adjust.

The other big question on the minds of students will be if a deep stop is a good thing or a bad thing. The answer is, we don't know. There hasn't been any convincing testing that gives a definitive answer either way in the context of a no-stop dive. My personal feeling is that if you feel like doing it, go ahead; however, all the 1 minute deep stop does in actual fact is slow down your ascent rate so do one if you want or ascend more slowly, if you want. For a no-stop dive the difference is going to be marginal to the point of being irrelevant.

R..

 

[dmaziuk]

The other big question on the minds of students will be if a deep stop is a good thing or a bad thing. The answer is, we don't know. There hasn't been any convincing testing that gives a definitive answer either way in the context of a no-stop dive. My personal feeling is that if you feel like doing it, go ahead; however, all the 1 minute deep stop does in actual fact is slow down your ascent rate so do one if you want or ascend more slowly, if you want. For a no-stop dive the difference is going to be marginal to the point of being irrelevant.

+1.

In the interest of nitpicking, Marroni's study concluded that for 25-minute dives to 25 metres, faster ascent rate with "deep" and shallow stops produced less Doppler echoes than slow linear ascents. That idea extrapolated to deeper and longer dives resulted in NEDU study and "deep stops considered harmful". If both are true, then you can't expect deep stops to do any good for any dive profiles other than Marroni's 25/25. They may, they may not.