| I'd like to clarify that the main reason for GF is to create deep stops. By adjusting the allowable supersaturation, it creates stops far deeper than the standard Buhlmann model.
Here is a dive with GF 100/100 which is Buhmann without the DSF (Depth Safety Factor)
The Drogon Dive Planner [v2:15]
========================================
Dive profile for default:
Step Depth SegT RunT Gas ppO2 END
================================================== =============
1 0.0-> 40.0 0:48 0:48 Nitrox 14 0.70 44
2 40.0-> 40.0 59:12 60:00 Nitrox 26 1.30 37
Deepest effective stop: 24m
Buhlmann + Gradient Factor decompression schedule:
Step Depth SegT RunT %MV Gas ppO2 END
================================================== =============
3 40.0-> 12.0 4:00 64:00 90.8 Nitrox 59 1.30 1
4 12.0-> 9.0 5:00 69:00 97.7 Nitrox 68 1.30 0
5 9.0-> 6.0 10:00 79:00 99.2 Nitrox 81 1.30 0
6 6.0-> 3.0 13:00 92:00 98.4 Oxygen 1.30 0
7 3.0-> 0.0 0:18 92:18 99.5
================================================== =============
Dive time: 1:00:00 Gradient Factors were used:
Ascent & Deco time: 0:32:18 Low factor: 100%
======== High factor: 100%
Total run time: 1:32:18
Ascent rate: 10, Descent rate: 50 (m/min) Total CNS: 51% OTUs: 136
CC Setpoints used:
Depth Setpoint CNS
==========================
* 50.9 CC CNS Total: 51%
Here is the same dive with GF 10/90:
The Drogon Dive Planner [v2:15]
========================================
Dive profile for default:
Step Depth SegT RunT Gas ppO2 END
================================================== =============
1 0.0-> 40.0 0:48 0:48 Nitrox 14 0.70 44
2 40.0-> 40.0 59:12 60:00 Nitrox 26 1.30 37
Deepest effective stop: 24m
Buhlmann + Gradient Factor decompression schedule:
Step Depth SegT RunT %MV Gas ppO2 END
================================================== =============
3 40.0-> 24.0 2:00 62:00 65.0 Nitrox 38 1.30 17
4 24.0-> 21.0 1:00 63:00 69.6 Nitrox 42 1.30 13
5 21.0-> 18.0 3:00 66:00 74.5 Nitrox 46 1.30 9
6 18.0-> 15.0 3:00 69:00 76.9 Nitrox 52 1.30 5
7 15.0-> 12.0 4:00 73:00 80.9 Nitrox 59 1.30 1
8 12.0-> 9.0 7:00 80:00 85.0 Nitrox 68 1.30 0
9 9.0-> 6.0 9:00 89:00 88.5 Nitrox 81 1.30 0
10 6.0-> 3.0 13:00 102:00 91.9 Oxygen 1.30 0
11 3.0-> 0.0 0:18 102:18 95.5
================================================== =============
Dive time: 1:00:00 Gradient Factors were used:
Ascent & Deco time: 0:42:18 Low factor: 10%
======== High factor: 90%
Total run time: 1:42:18
Ascent rate: 10, Descent rate: 50 (m/min) Total CNS: 56% OTUs: 150
CC Setpoints used:
Depth Setpoint CNS
==========================
* 56.5 CC CNS Total: 56%
There are a couple of things happening here. The first is that the dive plan is about 10 minutes longer. The second is that the stops are significantly deeper.
Bubble models may model decompression more accurately, particularly with long deep dives, but GF is a good tool for incorporating deep stops in Buhlmann profiles.
There is still a lot to learn about how to do dives to 100m+ but it seems clear that deeper stops and slower ascents are a good thing on all decompression dives.
Bruce Partridge
Shearwater Research Inc. |