ceiling/GF

[Shearwater]

I think that it should be eliminated, as I don't think that it has meaning before the first stop.

Ken, correct me if I'm misinterpreting your post, but I think that you said that it should extend to the right of the first stop but with a different slope to reflect the ceilings that are continually generated between initial ascent and the first stop?

Version #5. Cheers.

 

[atdotde]

I am not with @rsingler. I would phrase the same type of ascent differently: imagine a diver that is afraid of breaking the ceiling and thus stays consistently one foot below the planned stop. That can be save with a dive computer that factors in that the off gassing is slightly less effective. I would argue that that diver essentially follows the plan but never reaches the first stop. So technically he never gets to the starting point of the deco and GFlow is never anchored. To me that does not make sense. The depth dependent gradient factor should not depend on a singular event like first touching the ceiling (which is not too different from violating the ceiling).
If you look at real profiles of dives red out from a dive computer you see that touching the ceiling hardly ever happens.
Therefore, for subsurface it was decided to go use a more robust criterion: throughout the dive compute the ceiling (assuming GFlow) and take the deepest of those as the anchor for the gradient factor interpolation. The difference to planned dives that gave a well defined first stop is minimal but for slightly slow or slightly deep ascends this works much better

 

[rsingler]

Good point @atdotde . It would be interesting to see what Shearwater says about exactly this scenario. It seems to me, tho', that a diver who stays just below the ceiling (and therefore maybe doesn't anchor the GFLo), is nonetheless offgassing as planned for that gradient, at least in the beginning. In other words, as soon as he ascends, he "violates the ceiling" of the stop he never met, but during the time he was offgassing, the requirement for that stop disappeared in the computer as it did realtime computations of theoretical N2 accumulation. I think it amounts to following the profile, at least at the beginning. What happens next is then interesting, and @Shearwater would need to speak to this: at the next stop, what GF is applied? It might be that the GF Lo anchor was applied the moment the diver broke thru the first stop. But if that stop requirement disappeared, the new first stop might be at GF30, and the diver might theoretically be following a GF30/30 profile all the way to the surface as the required stops disappeared. Have I got your thoughts correct? Can't wait to hear what the programmers say.

 

[lermontov]

Version #5. Cheers.

awesome now lets work on a descent line

 

[lermontov]

Good point @atdotde . It seems to me, tho', that a diver who stays just below the ceiling (and therefore maybe doesn't anchor the GFLo), is nonetheless offgassing as planned for that gradient, at least in the beginning. In other words, as soon as he ascends, he "violates the ceiling" of the stop he never met, but during the time he was offgassing, the requirement for that stop disappeared in the computer as it did realtime computations of theoretical N2 accumulation. I think it amounts to following the profile, at least at the beginning. What happens next is then interesting, and @Shearwater would need to speak to this: at the next stop, what GF is applied? It might be that the GF Lo anchor was applied the moment the diver broke thru the first stop. But if that stop requirement disappeared, the new first stop might be at GF30, and the diver might theoretically be following a GF30/30 profile all the way to the surface as the required stops disappeared. Have I got your thoughts correct? Can't wait to hear what the programmers say.

well based on real time calculations the DC projects the first stop based on the set GF at the depth the DC is at regardless otherwise youd never know how much deco you had to do until you broke AP line so the GF lo is 'anchored' based on a projecton on an ascent at that moment in time, and that will change ie a moving target as you slowly ascend and clear some deco as you take pics etc adding more or less deco as you swim around

 

[rsingler]

But @atdotde has a good point. As that moving target GFLo is determined by your accumulated depth/time, it is fixed at GF30 (or whatever). If you clear stops based on a gradual ascent (below GF30) the next calculated first stop is still at GF30. Unless the GFLo is anchored some other way, you could ascend at "GF31/31" all the way to the surface, never triggering the transition to GFHi.
I don't know how the programmers at Shearwater trigger the transition. On a planner, it's set in stone. Or am I misunderstanding how this works on dive computers completely?

 

[lermontov]

But @atdotde has a good point. As that moving target GFLo is determined by your accumulated depth/time, it is fixed at GF30 (or whatever). If you clear stops based on a gradual ascent (below GF30) the next calculated first stop is still at GF30. Unless the GFLo is anchored some other way, you could ascend at "GF31/31" all the way to the surface, never triggering the transition to GFHi.
I don't know how the programmers at Shearwater trigger the transition. On a planner, it's set in stone. Or am I misunderstanding how this works on dive computers completely?

the way I understand it and as you get close to the surface that GF gets steeper and steeper as its angle ratio is over a lesser depth but ( and Im guesing) id suspect youd have lots of micro stops and would be easy to violate the ceiling
in regard to the programming shearwater have a @+5 setting which might be a clue as to how they set up the GF issues

 

[lermontov]

I still have some question about swimming up the AP( or even a little below it) - and you (according to @doctormike) arent off gassing then what happens when you get to say 6mm? 4m? 1m? .5m? it seems theoretically possible based on the graph that theres no deco ? so is the graph an accurate representation of the AP line as it shows it finishing at surface?

 

[doctormike]

I still have some question about swimming up the AP( or even a little below it) - and you (according to @doctormike) arent off gassing then what happens when you get to say 6mm? 4m? 1m? .5m? it seems theoretically possible based on the graph that theres no deco ? so is the graph an accurate representation of the AP line as it shows it finishing at surface?

Sorry, I think that you misunderstood.

Of course if you ascend, you offgas. I was just making the point that there is no such thing as "swimming up the AP", because as soon as you ascend, you generate a pressure gradient between a leading, saturated tissue compartment and the gas that you are breathing. This happens because the PPN2 of the inspired gas changes instantly, while the tissue PPN2 takes a non-zero amount of time to change as nitrogen leaves the tissue, restoring a Henry's law equilibrium.

So every ascent is a departure from the AP line, followed by an eventual return to the AP line if you don't ascend any further. If you do stop for a while, drop back towards the AP line but then continue your ascent, you get the stepped ascent line in the drawing.

 

[lermontov]

Sorry, I think that you misunderstood.

Of course if you ascend, you offgas. I was just making the point that there is no such thing as "swimming up the AP", because as soon as you ascend, you generate a pressure gradient between a leading, saturated tissue compartment and the gas that you are breathing. This happens because the PPN2 of the inspired gas changes instantly, while the tissue PPN2 takes a non-zero amount of time to change as nitrogen leaves the tissue, restoring a Henry's law equilibrium.

So every ascent is a departure from the AP line, followed by an eventual return to the AP line if you don't ascend any further. If you do stop for a while, drop back towards the AP line but then continue your ascent, you get the stepped ascent line in the drawing.

lol of course