How do you pre-plan a multilevel dive or do you? Do you plan the dive using a manual approach (table or other method) or do you use a paid subscription software application?
Does your pre-plan include your expected RMV, gas volume and time requirements to stay within the NDLs? Or do you jump in and monitor on the fly your dive based on your SPG (AI) and PDC?
It can be a boat or shore dive - I am interested in your approach to a pre-plan or lack of pre-plan.
Thanks in advance.
Given you are an advanced diver in recreational open water with a
1 bar/min per ATA pressure Surface Consumption Rate for a particular tank, then all you need for planning multi-levels are the depths in ATA, the time you spent at each multi-level depth, and then you can figure out your air consumption for each particular depth, confirming it with an SPG or AI reading. For the following the multi-level profile below in case of a malfunctioning Dive Computer at depth, conservatively treat it as a contingent NDL 18 meters for 50 minutes Air Table Dive, and probably abort early as needed to an ascent & Safety Stop.
So you descend to 30 meters depth; that's 4 ATA (30 divided-by 10 plus 1 equals 4 ATA); you stay 5 minutes. 1 bar/min per ATA multiplied by 4 ATA multiplied by 5 minutes equals 20 bar consumed. Confirm with SPG or AI, your delta remaining pressure reads 20 bar less --so if you start with a full tank of 200 bar, the SPG or AI should indicate "180 bar". (200 minus 20 is 180 bar). Rock Bottom minimum gas reserve for buddy air sharing is 60 bar for this max depth, and with 180 bar remaining, you've got plenty for a Buddy Out-of-Air Emergency.
You then ascend to 21 meters depth; that's 3.1 ATA (21 divided-by 10 plus 1 equals 3.1 ATA); you stay 10 minutes. 1 bar/min per ATA multiplied by 3.1 ATA multiplied by 10 minutes equals 31 bar consumed. Confirm with SPG or AI, your delta remaining pressure reads 31 bar less --SPG or AI should indicate "149 bar". (180 minus 31 is 149 bar).
You then ascend to 15 meters depth; that's 2.5 ATA (15 divided-by 10 plus 1 equals 2.5 ATA); you stay 30 minutes. 1 bar/min per ATA multiplied by 2.5 ATA multiplied by 30 minutes equals 75 bar consumed. Confirm with SPG or AI, your delta remaining pressure reads 75 bar less --SPG or AI should indicate "74 bar". (149 minus 75 is 74 bar).
Finally ascend to 6 meters depth; that's 1.6 ATA ( 6 divided-by 10 plus 1 equals 1.6 ATA); you stay 10 minutes. 1 bar/min per ATA multiplied by 1.6 ATA multiplied by 10 minutes equals 16 bar consumed. Confirm with SPG or AI, your delta remaining pressure reads 16 bar less --SPG or AI should indicate "58 bar". (74 minus 16 is 58 bar).
Do a slow ascent to the surface --on the surface inflate your BCD/Wing/Drysuit and you know even before looking at your SPG that you have 50 bar remaining in your tank.
You should check your SPG or AI over an arbitrary elapsed dive time interval like every ten minutes, or every five minutes if deeper than 21 meters. If the expected SPG or AI reading is 30% or more than you figured, then that indicates you are physically working & breathing harder than normal, or have a leak somewhere in your reg/gear set-up, and should consider aborting the dive.
