Deep Dive into Reading

Ratio Deco 1:2 with 2 Decompression bottles


Standardized Gas Mixes:

  • Bottom gas mix: 18/45, Deco gas mix: Nitrox 50 and oxygen
  • Range: 51 m ~ 72 m
  • Bottom time: 10 min. ~ 120 min.
  • Set point: 60 m.
  • Relationship between bottom time and the amount of deco: 1:2
  • Deco time division:
    • halftime from 21 m. ~ 6m. on Nitrox 50
    • Halftime from 6 m. up on oxygen + super slow ascent to the surface if is it possible, according to the environment conditions.

Setpoint Table

Depth (meters)Time (minutes)
51(BT x 2) -15
54(BT x 2) -10
57(BT x 2) -5
601:2= BT x 2 (setpoint)
63(BT x 2) +5
66(BT x 2) +10
69(BT x 2) +15
72(BT x 2) +20
Deep stop0~59 minutes of deco60~89 minutes of deco
50 % of the depth 12
60 % of the depth1
Deep Stop table

Example:

A diver goes before starting the ascent to the surface below the average depth (AD), down to 57 meters, although most of the time was spent at 54 meters. The total amount of bottom time was 20 minutes.

First, locate the set point: 60 meters, then multiply by 2 the BT and subtract 5 minutes to the total amount of time as it is shown in the table: (20 min.x2) – 5min. = 35 min. of total deco time TDT.

Second, divide by 2 the TDT and assign each halftime to 21 meters up to 6 meters and halftime to 6 meters up. In this case, to make the calculation easier on the fly, I’ll use 34 minutes as TDT, divide by 2 is 17 minutes each half, then I will add the remaining minute to the 6 meters stop:

Mental Calculations: 35/2
  • 30 /2 = 15
  • 4 /2= 2
  • 15+2= 17 first segment
  • 15+2+1= 18 second segment
Depth Stops:
  • 50% of depth: 27 meters
  • Time to reach 27 meters: 3 minutes
  • 1 minute at deep stop (exponentially up to 21 meters) + ascent to 21 meters.
DepthInitial time: 17Curve S
2133
1832
1532
1234
93+26
Take a break from Nitrox 50 at 9 meters for 3 minutes on back gas

The idea behind this is to take a break from high PO2 and prepare for gas change from the back gas to the oxygen bottle, this will add some consistency in the procedure.

Shallow stops

As it’s oxygen, you will spend most of the time at 6 meters then a super slow ascent from the 3 meters stops, 1 minute for each meter. All of it will depend on environmental factors.

6 meters: 15 minutes, 3 meters: 3 min. + 3 min. ascent to the surface.

Profile
Depth (meters)Stop (minutes)
5720
ascent3
271
242
213
182
152
124
96
615
3 up to surface6

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