Subsurface 5.0 has been released

[dmaziuk]

ZH-L has nothing to "smooth out" the transition from "no-stop" to deco, but 60 minutes is ridiculous. Esp. on a 10-minute dive to 28 msw: that's not even a "optional stop shall be mandatory" dive by DSAT tables. (What's you GF setting?)

I.e. at first glance this does not look right.

 

[inquis]

When 6 meters is infinite NDL, it's not a stretch to me that NDL at 10 m is an hour. It's the fast tissues that were primarily loaded -- and cleared -- on such a short dive.

 

[inquis]

Esp. on a 10-minute dive to 28 msw: that's not even a "optional stop shall be mandatory" dive by DSAT tables

No question they were in deco. However, they cleared during the slow ascent. Not uncommon in the "light deco" regime.

 

[inquis]

What's you GF setting?

Looks like GFHigh of 75.

 

[Walde]

The rec planner extends the time at the last point until NDL or gas runs out. It appears to me that you surface slowly enough in the 10 min ascent to still be in deco at your last defined point, so SubS gets you to the surface ASAP. In the 9 min ascent (less tissue loading) you barely cleared and are not in deco. Time is therefore extended.

So on the 9 min ascent I'm cleared and I could surface and SubSurface just shows me that I Can continue diving for extra 60 minutes?

 

[atdotde]

I claim it works as it should. The long version of the dive is limited by gas. Ignoring the amount of gas available would be an infinite time at that depth.

The difference between the two versions is in the 19min half time tissue (as you can see by reading the info box carefully): If you spend a bit more time on your way up to 10m, you saturate that tissue just that little bit more that it produces a ceiling that at 10m would take quite a while to clear. So that would trigger the dive to be a mandatory stop dive. To avoid that you have to ascend from 10m. The difference is so extreme as with your setting of gradient factors 10m is very close to the depth where the saturation pressure is very close to the maximal surfacing tissue pressure.

To get a feel for this, turn off the safety stop (as that obscures matters a bit), add another segment of say 1min at 10m and then move the waypoints around by a bit (you can do that using the cursor keys after selecting a waypoint with the mouse in the profile plot). You will find that it does not take much moving to turn the profile red meaning that the dive became a deco dive despite being in recreational mode (or you turn that off as well to see proper stops).

 

[dmaziuk]

When 6 meters is infinite NDL, it's not a stretch to me that NDL at 10 m is an hour. It's the fast tissues that were primarily loaded -- and cleared -- on such a short dive.

I should've been more careful with the wording: I don't have a problem with an hour at 10 metres, Haldane called that no-stop depth ("infinite NDL") and that's good enough for me. It's the jump from nothing to an hour that looks silly. But I suppose we always knew there's a discontinuity between "no-stop" and "yes-stop", we're bound to find degenerate cases if we look hard enough.

 

[inquis]

So on the 9 min ascent I'm cleared and I could surface and SubSurface just shows me that I Can continue diving for extra 60 minutes?

Yes. The effective logic that is evaluated at your last defined point is this:

1. If in deco, surface as soon as deco+safety stops will allow​

2. If not in deco (i.e., you're clear), surface when gas reaches the defined reserve level​

On the 10 min ascent, the first is triggered. On the 9 min ascent, the second is triggered.

I'm a little worried that you're planning decompression profiles at this stage (if your dive count is accurate), but hopefully it was just general curiosity/exploration of the software. FWIW, if looking for longer bottom times, nitrox is the next step.

 

[inquis]

It's the jump from nothing to an hour that looks silly.

You're right, the intuition is there's little difference in the tissue loading, so there shouldn't be a huge difference in runtime. It's the different dive termination logic that's making it look odd rather than any discontinuity between no-stop and yes-stop.

 

[dmaziuk]

You're right, the intuition is there's little difference in the tissue loading, so there shouldn't be a huge difference in runtime. It's the different dive termination logic that's making it look odd rather than any discontinuity between no-stop and yes-stop.

"Termination logic" is a cop-out (with all due respect to Robert): don't we assume a perfectly spherical diver of uniform density with infinitely large cylinder?