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Just starting to think about twins, yes its the Nitrox course thats done it for me. Proper dive/gas management is to start the ascent with 50bar in the tank although some say come up with 50 bar remaining at the surface. I tend, rightly or wrongly to start the ascent if I'm at 20m with 50 remaining, if I was deeper I'd start a bit earlier. I usually end up at the surface with 30bar.
So I calculate my bootom time base on available gas (Fill pressure - 50bar) and multiply by tank size divide by consumption rate (based on 25sac - so 100 l/min at 30) [1]
Now if I run twins can I assume availabe gas is
tank 1 Max fill - nominal amount (say 20bar) x size
tank 2 max fill - 50 bar. x size
so for twin 10's at 220 bar I'd have
tank 1 (220 - 20) x 10 = 2000 ltrs
tank 2 (220 - 50) x 10 = 1700 ltrs
total = 3700 ltrs
In theory 3700/100 = 37 mins for a 30m dive, I have ignored travel time to keep it easy but would include that in calcs in the real world.
[1] My sac hasnt dropped over the last 30 dives and its still at 25l/min if I use (press in - press out) x capacity/corrected press average(i.e. divide by 4 for a 30m dive) x time of dive
e.g. 220 in - 50 out x12 = 2040 ltrs
dive time (to start of ascent) = 33mins
av depth = 15m
corrected press av. = 2.5
2040 /(33 x 2.5) = 25L/min average.
maybe it will get better maybe it wont, who knows but I think my reg is partly to blame as it throws so much gas at me that most of it seems to get exhasuted away. As soon as I stop breathing in I can hear/see/feel exhaust gas coming out of it, is that 'normal'?
So many questions for a Friday, sorry guys.
Matt.
Just starting to think about twins, yes its the Nitrox course thats done it for me. Proper dive/gas management is to start the ascent with 50bar in the tank although some say come up with 50 bar remaining at the surface. I tend, rightly or wrongly to start the ascent if I'm at 20m with 50 remaining, if I was deeper I'd start a bit earlier. I usually end up at the surface with 30bar.
So I calculate my bootom time base on available gas (Fill pressure - 50bar) and multiply by tank size divide by consumption rate (based on 25sac - so 100 l/min at 30) [1]
Now if I run twins can I assume availabe gas is
tank 1 Max fill - nominal amount (say 20bar) x size
tank 2 max fill - 50 bar. x size
so for twin 10's at 220 bar I'd have
tank 1 (220 - 20) x 10 = 2000 ltrs
tank 2 (220 - 50) x 10 = 1700 ltrs
total = 3700 ltrs
In theory 3700/100 = 37 mins for a 30m dive, I have ignored travel time to keep it easy but would include that in calcs in the real world.
[1] My sac hasnt dropped over the last 30 dives and its still at 25l/min if I use (press in - press out) x capacity/corrected press average(i.e. divide by 4 for a 30m dive) x time of dive
e.g. 220 in - 50 out x12 = 2040 ltrs
dive time (to start of ascent) = 33mins
av depth = 15m
corrected press av. = 2.5
2040 /(33 x 2.5) = 25L/min average.
maybe it will get better maybe it wont, who knows but I think my reg is partly to blame as it throws so much gas at me that most of it seems to get exhasuted away. As soon as I stop breathing in I can hear/see/feel exhaust gas coming out of it, is that 'normal'?
So many questions for a Friday, sorry guys.
Matt.