Padi Advanced OW - Deep stops??

[KenGordon]

I disagree, I dive DSAT. I use DSAT NDLs for my no stop diving. Many divers do a 5 minute safety stop rather than 3 minutes. The Shearwater computers have a set 3, 4, or 5 minute safety stop in rec mode as well as the adaptive setting. The adaptive setting gives a 3 minute SS unless the dive is greater than 100 feet or comes within 5 minutes deco, in which case, the SS is 5 minutes. My strategy is something like that, on the conservative side. Adding a deep stop to my rec dives would not be consistent with diving DSAT, it might even turn a no stop dive into a deco dive. I use standard ascent rates.

For deco diving, I follow and clear the computer deco stops. I don't think I would be faulted for adding a little extra time at 10-15 feet after clearing deco, again, on the conservative side.

My goal is to return to the surface safely, so far, so good.

Good diving, Craig

I am not saying there is anything wrong with adding extra shallow stops. My point is that it makes it something other than DSAT. If I were to dive a proper ZHL-16b (no gf) profile and then add 10 minutes at 3 minutes what am I doing? Can I claim anything about raw ZHL-16b based on that?

 

[Diver0001]

If he had followed our written plan (plus the deep stops and oxygen window stops) instead of the computer, he would have done relatively short shallow stops and been out of the water 20 minutes sooner--to what effect?????

So the short story here is that he made a safe dive, you made a safe dive and nobody got bent.

The complication is that you were not able to stay together in a group during the ascent. This increases risk, especially, in your case, to the diver who was left twisting in the wind by himself with an ever decreasing air supply.

And THAT is the reason that technical divers need to not only square off in terms of gasses but also procedures.

Years ago I used to dive with someone who was a strong believer in RGBM. I was using Buhlmann. After some initial problems with alignment like you described, we finally settled on doing his deep ascent (notice I am not saying deep stops) and then my shallow stops from the point at which his ceiling caught up with mine. It resulted in longer dives than either algorithm would have prescribed alone but both of us were able to dive the algorithm that made us feel most comfortable and we were able to stay together during the ascent, which we believed was important.

These days I still dive a different algorithm than my buddy. He dives with a Petrel on Buhlmann with 30/70 and has a Suunto RGBM-like thing as a back up. On nitrox dives, I dive an old Vytec, from before Suunto started bubble-wrapping their Buhlmann.... The main difference is the ceiling. My computer and the Petrel calculate within a minute or two the same TOTAL deco obligation (which is the only number I need/want to know, hence the old Vytec). That's not strange, it's pretty much the same algorithm. His computer often picks a deeper line from about 15 metres and up because of the GF-lo while mine is very persistent is keeping the ceiling around 3 to 4 metres until you are at least 30 minutes over the NDL.

In the course of many many dives I've developed an ascent strategy based on input that I got from, among others, some people online, like Steve Lewis. The idea of all the "deep stops" we do is to limit the ascent speed, and amazingly by just slowing down the ascent to 3m per minute from the 18 metre stop and onward, his "deep stops" usually clear before we get there and the difference to the dive only shows up at 9 metres. We are usually back at 18m for the gas switch before the hour is up so the controlling tissue from the Buhlmann algorithm isn't saturated yet. This stop is usually extended in order to do gas changes because we're almost always free-hanging in a 3m bubble of green at this point and we need to be accurate about depth.

We often make a particular dive that involves 30 odd minutes of deco so I know that if I ascend like this and put in a 4 minute stop at 9m that we can then ascend to 6 and finish our deco based upon the respective eccentricities of our computers without extending the dive any more than about 4 minutes.

So yeah, you can align two different algorithms or even an algorithm and an ascent strategy (as I do) without it affecting the total deco very much. The point is to make the right choices and for the right reasons.

R..

 

[scubadada]

I am not saying there is anything wrong with adding extra shallow stops. My point is that it makes it something other than DSAT. If I were to dive a proper ZHL-16b (no gf) profile and then add 10 minutes at 3 minutes what am I doing? Can I claim anything about raw ZHL-16b based on that?

Hi Ken,

OK, I don't think we're really arguing about anything.

Unlike the PADI RDP table, there are no mandatory safety stops using computer DSAT. I dive a VT3 primary and a Geo2 backup, both allow me to choose no SS, or a 3-5 minute safety stop, at 20, 15, or 10 feet. "Raw" DSAT is probably anything in this range. I happen to use the longer safety stop when I have approached close to deco. Using a SS of some kind is the standard in no stop diving, regardless of decompression algorithm. This thread was started regarding no deco deep stops, I have chosen not to do them.

After fulfilling my deco obligation, I add the equivalent of a SS to the 10 foot deco stop. If this is not raw DSAT, because I do not ascend directly from the last stop, so be it.

Good diving, Craig

 

[EFX]

After reading through this thread and a few others I don't understand why some divers are making ad hoc adjustments to their dive plan instead of just following their computer. For example, one diver inserted a deep stop that his computer didn't call for. Another diver said instead of doing a SS at 15 ft for 3 minutes he does 3 minutes at 20 ft. followed by 5 minutes at 15 ft. Now, don't get me wrong. I'm not against making dives more conservative when needed. But, why not set your computer to a more conservative setting and follow it? Why invent extra rules? I'm not talking about changes during a dive, i.e. you work harder than planned at depth. In that case the extra time at the SS is called for. I'm talking about a rigid routine that isn't based on the particular dive environment.

If you're doing multiple dives per day, day after day, i.e. live-aboard, all that extra time in the shallows is going to limit bottom time on future dives. For rec divers doing maybe 3 dives a day for two days in a row won't make much difference but why do it anyway?

 

[rjack321]

If you're doing multiple dives per day, day after day, i.e. live-aboard, all that extra time in the shallows is going to limit bottom time on future dives.

All that extra time in the shallows is deco time. Maybe the computer didn't require it, but there is zero downside to do 5 (or more) extra minutes in the 10 to 20ft range. That's not on-gassing that's extra off-gassing. Its not going to limit future dives unless you are diving tables and using your max depth and total runtime to calculate your pressure group.

 

[dmaziuk]

If you're doing multiple dives per day, day after day, i.e. live-aboard, all that extra time in the shallows is going to limit bottom time on future dives. For rec divers doing maybe 3 dives a day for two days in a row won't make much difference but why do it anyway?

That's actually questionable and depends on your definition of "shallows". E.g. from my vague picture of bubble theories, their off-gassing should be more efficient at the safety stop depths then at the surface. From observing my RGBM computer's behaviour I can tell you that its idea of SS depth lies somewhere near no-limit depth -- or at least it if I spend enough time above 7-8 m, it won't even turn the SS icon on as I get to teh "textbook" 5-3 m. So I wouldn't be surprised if on some computers all that extra time at around 5 m would actually do the opposite, in the sense that they'll give you more bottom time than if you went straight up and spent that time topside instead.

 

[Jim Lapenta]

I personally find a stop for a minute at half max depth on a no mandatory deco dive serves a couple of purposes. It gives me a chance to slow down and make any necessary adjustments to buoyancy, gear, etc. It allows me to make sure my buddies are ok and also in control.

I know once I make that initial stop at say 50 feet on a 100 ft dive and then make a minute stop every ten feet until I surface I physically feel better. After having a serious reverse block a few years back I am very careful with ascents.

I know that this, for me, allows me to off gas with less stress on my body. Same reason I'll take 2 -10 minutes to come up from 15 feet. Plus I get to see some pretty cool stuff at times that others miss.
My NDL bottom times are also often shorter than others. This is due to using a 30 ft per minute descent or less due to equalization concerns.

These are no decompression dives. Depending on whose definition you use one agency says bottom time is time from surface til you start your ascent. Another says until you reach the safety stop. Ideally you decide your level of conservatism. The other concern with adding stops is making sure you have the gas to do them if you do decide to. This is part of the reason we (SEI) teach deco tables in the OW class along with gas management. Not so divers can do deco dives but in some cases show why they should pay attention to depth, time, and how much gas they have.

Even when you only decide to extend the safety stop to 5-8 minutes, having enough gas to do that is kinda important. I remember seeing an AOW class asked right before their deep dive what they need to do should they run over the NDL for the dive. Blank looks. Even more disturbing was the instructor still took them on the dive. After telling them to extend the stop. He never told them why or that the dive was now a mandatory decompression stop dive.

 

[DevonDiver]

After reading through this thread and a few others I don't understand why some divers are making ad hoc adjustments to their dive plan instead of just following their computer.

Because there's a difference between simplest and the most optimum approach.

The majority of divers benefit from having the simplest safe approach.

A minority of divers seek an optimum approach, possessing a capability and understanding to apply approaches that are more complex.

 

[scubadada]

Because there's a difference between simplest and the most optimum approach.

The majority of divers benefit from having the simplest safe approach.

A minority of divers seek an optimum approach, possessing a capability and understanding to apply approaches that are more complex.

I don't think you're saying that no deco deep stops are the optimum approach in this case, correct?

 

[KenGordon]

All that extra time in the shallows is deco time. Maybe the computer didn't require it, but there is zero downside to do 5 (or more) extra minutes in the 10 to 20ft range. That's not on-gassing that's extra off-gassing. Its not going to limit future dives unless you are diving tables and using your max depth and total runtime to calculate your pressure group.

No, it is slower off gassing in the water (on air) than at the surface. You will deco quicker, but with more stress, at the surface. Thus taking longer to get out of the water will mean a bigger gas load at the start of the next dive according to classical dissolved gas models, assuming the same start time for the second dive.