Situation
– Diving in a buddy team
– Diving a wreck at 40 m for 20 min in the sea
– No penetration dive (deco always startable)
– Diving OC with just back gas (one type of gas)
– The only dive for that day
Configuration
Gas
– The max. ppO2 shall be 1.4 bar, so for 40 meter we have to choose EAN28 (Travel, Bottom, Deco Gas)
– The deco could be shorter if another gas with a higher oxygen level would be used there
RMV: Bottom: 20 l/min, Deco: 20 l/min
– Normally the RMV is depending on the depth in contrast to the SAC, but here they just mean the SAC
– Varies for every person and even then it’s based on the situation (e.g. temperature, stress level, …)
Descent/Ascent rate:
– Descent (surface to bottom): 15 m/min
– Ascent (bottom to first deco): 8 m/min, Deco: 6 m/min, Surface (last deco to surface): 6 m/min
Deco model: VPM-B (+2)
– Varying Permeability Model (with Boyle’s Law compensation)
– The argument defines the level of conservatism
Result
Dive profile
Dive details
Gas consumption (manual calculation)
Gas for Dive = Gas for Descent + Gas for Bottom + Gas for Deco
Gas for Descent = RMV(0 to 40m) * Time(0 to 40m)
= RMV20m * Time(0 to 40m)
= 3 * SAC * Time(0 to 40m)
= 3 * 20 l/min * 2:40 min
= 3 * 1/3 l/sec * 160 sec
= 160 l (≠ 159 l)
Gas for Bottom = RMV40m * Time40m
= 5 * SAC * Time40m
= 5 * 20 l/min * 17:20 min
= 5 * 1/3 l/sec * 1040 sec
≈ 1733 l (≠ 1723 l)
Gas for Deco = ...
Description
V-Planner 3,103 by Ross Hemingway, VPM code by Erik C. Baker. Decompression model: VPM - B DIVE PLAN Surface interval = 1 day 0 hr 0 min. Elevation = 0m Conservatism = + 2 Dec to 40m (2) Nitrox 28 15m/min descent. Level 40m 17:20 (20) Nitrox 28 1,39 ppO2, 36m ead Asc to 15m (23) Nitrox 28 -8m/min ascent. Stop at 15m 0:53 (24) Nitrox 28 0,70 ppO2, 13m ead Stop at 12m 1:00 (25) Nitrox 28 0,61 ppO2, 10m ead Stop at 9m 2:00 (27) Nitrox 28 0,53 ppO2, 7m ead Stop at 6m 5:00 (32) Nitrox 28 0,45 ppO2, 5m ead Stop at 3m 7:00 (39) Nitrox 28 0,36 ppO2, 2m ead Surface (39) Nitrox 28 -6m/min ascent. Off gassing starts at 23,9m OTU's this dive: 35 CNS Total: 13,9% Gas density: 6,0g/l 2636,6 ltr Nitrox 28 2636,6 ltr TOTAL DIVE PLAN COMPLETE ********* WARNING & DISCLAIMER ********* This V-Planner generated dive schedule could indirectly kill you. ...
Implication
Reserve
– The calculated amount of necessary breathing gas is without any reserve yet
– You can get the necessary values from the Dive details table (they are rounded)
The worst case you should be prepared for is if one of you lost all their gas right before the deco.
Reserve = Gas for Deco (SAC of buddy, here it's the same)
= Gas for Dive - (Gas for Descent + Gas for Bottom)
≈ 2637 l - (159 l + 1723 l)
= 755 l
Gas for Dive + Reserve ≈ 2637 l + 755 l
= 3392 l
This should definitely be rounded up, cause the gas consumption will be increased in an emergency.
Tanks
A good choice would be a double pack of 12 l tanks at 200 bar (finishing at 50 bar).
Gas in Tanks (200 bar to 50 bar) = 2 * 12 l * 150 bar = 3600 l > 3392 l