Overshooting NDL and mandatory deco stops

[Manatee Diver]

4) A safety stop, while not mandatory, is still a good idea, and shouldn't be omitted. The reason for this is that many divers will inadvertently violate an ascent rate or NDL to a small degree during the dive, increasing decompression stress without their computer necessarily giving them a mandatory stop. The safety stop is an extra safety buffer in this instance. Also, people tend to ascend faster when they are almost at the surface, figuring that the dangerous part of the dive is done. By always doing a safety stop, you make this less likely.

5) You should avoid a sawtooth dive profile, with multiple ascents within a dive. This is how I ended up taking a chamber ride despite my computer saying that I was "safe".

The bolded sections are why I wonder if the bubble model guys are right in theory, but their solution of a ton of stops at deeper depths was the wrong way to go about it.

 

[NAUI Wowie]

@ScubadriverDale As usual, this thread has veered into the weeds. To address your original question, I'm attaching the profile of a dive through the "Devil's Throat" in Cozumel a few years ago. (It was my 25th dive and a total trust-me dive - I don't recommend it). I didn't have my Perdix yet, but was using an Amphos Air PDC (Pelagic Systems - type). The red region is when I slipped into "light" deco. The little boxes show what my computer would have shown at the 4 points I highlighted with arrows. Note that my deco obligation (mandatory - 3min at 10ft) was cleared by the time we had (slowly) worked back up to 40 ft. After that, it showed NDL time, which continued to increase during the safety stop. The only time I've had the Perdix in deco was in tech mode, so I can't show you exactly what it would say in rec-mode for "light deco". Probably quite similar to the Amphos.

And yes, I know I got back on the boat with less than 500 psi... so sue me! View attachment 497415

This graph was awesome thank you very much. It illustrated the answers to my questions.

 

[BRT]

The bolded sections are why I wonder if the bubble model guys are right in theory, but their solution of a ton of stops at deeper depths was the wrong way to go about it.

With the same absolute certainty that nitrox makes me feel better after a day of diving, I also am certain that a sawtooth profile makes me feel worse. Is that data????

 

[Manatee Diver]

No offense but you are starting to sound like my dad, he still refuses to use or buy cell phones because they arent necessary. Yes cell phones are not necessary to live and dive computers are not necessary to dive. When I got certified and for a few dives I used my diving watch and know how to use it. And I didnt die lol. BUT a dive computer is a great diving aid especially with air integration.

Who knows in 20 years divers may be diving inside diving air bubbles controlled via a hand computer.... And I may be you then saying nah I dont need that diving bubble to dive at all....

EDIT ah I see in your next post you are big into dive computers. It seemed on multiple posts on this thread you are almost kind of negative towards them.

What the Chairman is saying is that the most important tool for diving isn't the dive computer, or any other piece of equipment, but the squishy grey stuff between your ears.

 

[NAUI Wowie]

Post #22.
Someone asked the question on GF and your answer was "whatever the default setting". My interpretation of your reply was: No idea and please tell me what it is.
Yes, I was wrong in my interpretation.
But you do not have a clue on the setting of GF.

I knew that before I started the topic. and I dont have any need at all to know the setting of GF. Fact.

 

[NAUI Wowie]

After a DAN lecture with Dan Orr, it was obvious to me that I needed a longer safety stop. Neural fluid has about the same half time as blood at around five minutes. Making them 5 minutes has eliminated the need to take a nap afterwards. Those two extra minutes really make a difference.

So you absolutely noticed a difference making the optional safety stop at 15ft 2 minutes longer? Btw when I first started diving as soon as I surfaced I had this fizzing sensation in my head. I wasnt speeding to the surface but when later I tried stopping at about 5 feet and doing a super slow ascent these fizzing sensations stopped. Now even if I dont do the super slow last five feet I dont have that head fizz anymore but then again im still always going very slow.

 

[RayfromTX]

Hi Dale.
The reason that you might want to know which GF is appropriate for your diving is because it is possible to change it either on purpose without enough info to make a good choice, or by mistake when scrolling the menus. I dive on the medium setting 40/85 but if I have reason to question my overall health or I'm doing 4+ dives a day I might set it to high conservancy 30/70. It is simply a fudge factor that is applied to the most aggressive version of the dive algorithm that is used by Shearwater. You don't have to study deco science to understand what your settings should be so that you can check and confirm you are diving in a way that you decided for yourself.

Yes, the last 10 feet should be done very slowly like in a full minute. I think the fizzies have a bit to do with sinus passages equalizing on the way up. I could be wrong.

 

[NAUI Wowie]

If you want a proper answer to the question you posed in your OP (except "follow the instructions you got during OW class"), it'd be a good idea to learn some basic deco science.

You posted in Advanced, thus the answers you get will be... advanced. If you want the McDonald's answer, ask in Basic.

If you should want to learn and understand beyond PADI OW level, get Mike Powell's excellent book "Deco for divers".

Touch'e or touche' lol point made

 

[scubadada]

High conservancy in rec mode is 35/75, default in tec mode is 30/70

 

[NAUI Wowie]

Hi Dale.
The reason that you might want to know which GF is appropriate for your diving is because it is possible to change it either on purpose without enough info to make a good choice, or by mistake when scrolling the menus. I dive on the medium setting 40/85 but if I have reason to question my overall health or I'm doing 4+ dives a day I might set it to high conservancy 30/70. It is simply a fudge factor that is applied to the most aggressive version of the dive algorithm that is used by Shearwater. You don't have to study deco science to understand what your settings should be so that you can check and confirm you are diving in a way that you decided for yourself.

Yes, the last 10 feet should be done very slowly like in a full minute. I think the fizzies have a bit to do with sinus passages equalizing on the way up. I could be wrong.

I believe default was stated as most conservative 30/70 on the perdix. If I accidentally messed that up id reset defaults as soon as I was out of the water. I like to do liveaboards on the channel islands Socal so id prefer to be on most conservative settings as you can easily get up to 6 dives in a day with night dives included. I do only 32% nitrox on those trips.