How would you do this dive ...

[rjack321]

Ah ... got it. That makes sense.

... Bob (Grateful Diver)

The latest AG RD pdf has another way to make the deep stops proportional to the deco obligation. Basically a table. That's what I use although it only marginally applies to T1 level dives.

time greater than MDL - 50% up deep stop time
MDL - 1
15min -2
30min -3
45min -4
60min -5

 

[Dan Gibson]

I beleive it was on DIR Explorers list IIRC.

I don't come to the same conclusion myself, but then I'm no expert on this subject.

I always understood that the most efficient way was to utilize the partial pressure vacancy deep and press the gradient shallow while not overstaying the intermediate stops as it becomes counter productive, hence the s-shape. On the surface I just can't see how linear stops are better (unless speaking in terms of minimum stop times) and it seems like a lazy way to calculate distribution of stops. I just can't see it as more efficient. One side of me wants to say BS, but another side says shut up an listen to someone who is supposed to understand this stuff at a much higher evel than myself. My ears are open and the cotton is in my mouth Someone explain this to me if I'm missing something.

I had read somewhere that GUE had switched from trying to make a sigmoid curve out of each segment to doing the stops as linear stops, but we were taught, as I said, to add to the gas switch stops.

 

[rjack321]

I think the general attitude amongst the "linears" is that it doesn't make much difference. I have shaped and I have done linear. I'm doing 2-5 mins a stop depending on needed time and can't tell a hoot of a difference in how clean I feel.

 

[MXGratefulDiver]

My impression is that most ratio deco schedules are so conservative that it doesn't really make that much of a difference.

Not that it matters under normal circumstances ... if planned properly you've got plenty of gas, and there's no hurry to get out of the water. But if circumstances were NOT normal (e.g. a medical situation or torn drysuit), it might be different. Do these scenarios get discussed in Tech 1? And if so, what recommendations do they make for modifying the deco schedule in favor of addressing what may be a more pressing problem?

... Bob (Grateful Diver)

 

[rjack321]

Actually RD schedules are not super conservative for me, I pad the rules by 3-5 mins on the shallow end.

Given an emergency (e.g. flood) the general thrust is to not skip deep stops at all. Keep those bubbles from starting and potentially growing.

Do the switch. Then, if things get really bad blow off the shallowest deco and you'll be (hopefully) looking at Type 1 from the slowest tissues instead of Type 2 from the faster neuro tissues. At least that's what was taught/implied/discussed in my T1.

 

[lamont]

I think the general attitude amongst the "linears" is that it doesn't make much difference. I have shaped and I have done linear. I'm doing 2-5 mins a stop depending on needed time and can't tell a hoot of a difference in how clean I feel.

Had discussion with a "linear diver" about this a couple of weeks ago and the major strength is that you're not distracted doing a lot of playing around with figures in your head while coming up from a 320 fsw dive with 5 bottles... Better things to focus on than having a team arguing over a minute here or there that isn't going to make any overall difference... Definitely appeals to my "less bull****" filter...

YMMV.

(no idea how DIR this is, i'll ask week after next...)

 

[rjack321]

On the T1 dives I've shaped we've never had an argument, although we sometimes correct a minute here or there math error. Linear is definately easier to add up so that's an additional benefit there IMO.

But if shape vs. linear doesn't even make much difference, why argue about the exact shape either?

 

[Dan Gibson]

And that's the point I'm having problem with. On dives with shorter stops with gas switches, that probably would mean very little difference. Now on dives where one would be doing excessively long stops in the itermediate range; that just doesn't seem right to me. Seems to me one could end up ongassing some compartments unnecessarily and resulting in problems shallow. Then again, maybe scenario is outside what most would ever need to worry about.

if shape vs. linear doesn't even make much difference

 

[boomx5]

On the T1 dives I've shaped we've never had an argument, although we sometimes correct a minute here or there math error.

Same here. Although, it is kind of funny when one of us will look at the other guy and say, "hey, wanna move?" And the other guy says, "yeah, I guess so...if you want. Do you wanna move?" Then the other guy says, "sure, why not". Then we move. We don't always do it that way, but we know if the time is close and the shape is right then there are really no issues.

 

[rjack321]

And that's the point I'm having problem with. On dives with shorter stops with gas switches, that probably would mean very little difference. Now on dives where one would be doing excessively long stops in the itermediate range; that just doesn't seem right to me. Seems to me one could end up ongassing some compartments unnecessarily and resulting in problems shallow. Then again, maybe scenario is outside what most would ever need to worry about.

Those dives would be way beyond me or my practical interest.

This extended dive has some shaping going on, but not as much as you'd think:
Red Sea Explorers - The Devil's Crack