An Experiment

[Blackwood]

The 25 minutes at 40' is part of the dive profile, not a required stop.

"One claimed his comp called for a 25 minute deco stop"

Regardless, my previous statement stands. "It's like 90 for 20 followed by a bunch of deco." It's a non-issue even on the most conservative tables.

 

[Blackwood]

So, the old guys were right. You can use tables for ML dive planning. I can just imagine them looking down and smiling knowingly.

Of course you can. The question you have to answer is: where do pressure groups apply? At the surface or at depth?

 

[Paladin]

The pressure groups are used to determine residual nitrogen in the blood. They would apply both on the surface and at depth.

 

[Paladin]

Blackwood, were you referring to the reply I got on the other thread? If that's the case, I see what you're getting at.

 

[Blackwood]

The pressure groups are used to determine residual nitrogen in the blood. They would apply both on the surface and at depth.

The pressure groups printed on the (PADI) table assume you've done a 60FPM ascent to the surface (that's why it's "residual"). In other words, on a 90 foot profile, it assumes you've already done 1 and a half minutes of deco at 45 feet (2.4ATM). I suppose it's a minor point for an NDL discussion, but your loading at the surface and your loading at depth aren't one and the same.

Blackwood, were you referring to the reply I got on the other thread? If that's the case, I see what you're getting at.

I figured we were discussing the same profile.

 

[Kern]

I'm the 1 who posted the profile to your question in the other thread. I posted it because as Blackwood said, a 25 minute deco on that dive just seemed way OTT.

I would have thought that posting the schedule for all to see was reasonably definitive. But here it is again adjusted for the 5 minute SS & converted to feet.

DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0ft
Conservatism = Nominal

Dec to 90ft (1) Air 50ft/min descent.
Level 90ft 8:12 (10) Air 0.78 ppO2, 90ft ead
Asc to 70ft (10) Air -30ft/min ascent.
Level 70ft 21:00 (31) Air 0.65 ppO2, 70ft ead
Asc to 50ft (32) Air -30ft/min ascent.
Level 50ft 20:00 (52) Air 0.53 ppO2, 50ft ead
Asc to 20ft (53) Air -30ft/min ascent.
Asc to 15ft (53) Air -30ft/min ascent.
Level 15ft 5:00 (58) Air 0.31 ppO2, 15ft ead
Asc to 10ft (58) Air -30ft/min ascent.
Stop at 10ft 1:20 (60) Air 0.27 ppO2, 10ft ead
Surface (60) Air -30ft/min ascent.

OTU's this dive: 16
CNS Total: 8.1%

2997.2 ltr Air
2997.2 ltr TOTAL

PS I'v jus noticed that the profile you've used in this thread is different to the 1 you used in the original thread.

Your new profile would look like this if your SS was still at 15'.

Decompression model: VPM - B

DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0ft
Conservatism = Nominal

Dec to 100ft (2) Air 50ft/min descent.
Level 100ft 8:00 (10) Air 0.85 ppO2, 100ft ead
Asc to 70ft (11) Air -30ft/min ascent.
Level 70ft 10:00 (21) Air 0.65 ppO2, 70ft ead
Asc to 40ft (22) Air -30ft/min ascent.
Level 40ft 25:00 (47) Air 0.46 ppO2, 40ft ead
Asc to 20ft (47) Air -30ft/min ascent.
Asc to 15ft (47) Air -30ft/min ascent.
Level 15ft 5:00 (52) Air 0.31 ppO2, 15ft ead
Surface (53) Air -30ft/min ascent.

OTU's this dive: 11
CNS Total: 4.2%

2506.9 ltr Air
2506.9 ltr TOTAL

 

[Paladin]

The pressure groups printed on the (PADI) table assume you've done a 60FPM ascent to the surface (that's why it's "residual"). In other words, on a 90 foot profile, it assumes you've already done 1 and a half minutes of deco at 45 feet (2.4ATM). I suppose it's a minor point for an NDL discussion, but your loading at the surface and your loading at depth aren't one and the same.


Not exactly the same, perhaps, but close enough for rec diving if you don't try to cut it too close, wouldn't you think?

Thanks for participating in this little experiment, guys. It's only purpose was to explore a theory purely for the sake of a little knowledge gained.

 

[Atom]

Obviously didn't dive it but in the suunto dive planner (and these are pretty conservative computers) it won't put you into deco, you'll have 6 min of nodec time when you start ascending from 100', 8 min of nodec time when you start ascending from 70', and 34 min of nodec time when you start ascending from 40'. But you'll run out of gas before ascending if you have sac of 0.6 and are using an AL80 (unless I screwed up the cylinder configuration).

I also was wondering if you could plan multi-level dive using a table and a SI time of zero and once spent some time searching for that on SB. I can't find the thread and maybe somebody else can chime in, but from what I gathered the answer to that is....no. Or at least, doing it with the table will results in a dive profile that is less conservative than what you'd get with "The Wheel". I'll try to find that thread again and link it here.

Edit:

While searching for that particular thread I found a few other ones that seem to indicate that if you follow some rounding rules you can get pretty much the same result with the table than with the wheel.

Edit 2:

Found it.... http://www.scubaboard.com/forums/basic-scuba-discussions/286108-multi-level-diving.html

 

[Paladin]

Academic exercises aside, the best way to test the process would be to plan such a multi-level dive, then actually dive it using a computer. Then the theoretical could be compared to the actual. This might sound like a waste of time but, you never know, it might come in handy for someone sometime.

It's too cold here to do it now, but maybe next summer I might try it. I think it's worth exploring.

 

[Atom]

The suunto dive planner simulates that same algorithm used on their computer (complete with simulated computer display + actual tissue saturation graph), so I'm pretty sure diving it would give the same results.