What if [...] ? What if [...] ? What if [...] ?
Ah, the well known discussion technique of "Just asking questions" - or "JAQing off", as it's sometimes affectionately called :cool2: And, of course, with a side order of strawmen.
I've given up discussing with
Foxfish, but for the benefit of other, more open-minded divers, I'd like to show that each and every one of those strawmen is easy to deal with as long as you use a sensible method for determining min gas / rock bottom instead of "surfacing with 50 bar, but only God knows how I'm gonna do that":
how do you know your assumed ascent profile was correct.
Assuming an ascent profile of 5 m/min:
Ascent 30m -> 0m => Ascent time: 30/5 = 6 minutes
1 min @ 30m: 1*60*(30/10 + 1) = 240L
6 min @ 15m ave: 6*60*(15/10 + 1) = 900L
Safety stop 3 min at 5m (1.5 ATA): 3*60*(5/10 + 1) = 270L
Min gas including safety stop: 240L + 900L + 270L = 1410L, 117.5 bar in a 12L, round to 120 bar
What if you need 5 minutes at the bottom before an ascent?
5 min @ 30m: 5*60*(30/10 + 1) = 1200L
3 min @ 15m ave: 3*60*(15/10 + 1) = 450L
Safety stop 3 min at 5m (1.5 ATA): 3*60*(5/10 + 1) = 270L
Min gas including safety stop: 1200L + 450L + 270L = 1920L, 1920/12 = 160 bar in a 12L
What if you need 100 L/min for two anxious divers not 60 L/min?
1 min @ 30m: 1*100*(30/10 + 1) = 400L
3 min @ 15m ave: 3*100*(15/10 + 1) = 750L
Safety stop 3 min at 5m (1.5 ATA): 3*100*(5/10 + 1) = 450L
Min gas including safety stop: 400L + 750L + 450L = 1600L, 1600/12 =133 bar in a 12L, round to 140 bar
Incidentally, this is more or less what I did in my earliest min gas calculations, when my normal consumption rate was around 20SLM...
What if your ascent rate should be 4 m/minute rather than 9 m/minute in an emergency.
Ascent 30m -> 0m => Ascent time: 30/4 = 7.5 minutes
1 min @ 30m: 1*60*(30/10 + 1) = 240L
7.5 min @ 15m ave: 7.5*60*(15/10 + 1) = 1125L
Safety stop 3 min at 5m (1.5 ATA): 3*60*(5/10 + 1) = 270L
Min gas including safety stop: 240L + 1125L + 270L = 1635L, 1635/12 =137 bar in a 12L, round to 140 bar
Do we need to consider deep stops and extended safety stops during an emergency ascent.
Deep stop: 1 minute at 15m (2.5 ATA)
Extended safety stop: 5 minutes at 5m (1.5 ATA)
1 min @ 30m: 1*60*(30/10 + 1) = 240L
3 min @ 15m ave: 3*60*(15/10 + 1) = 450L
Deep stop 1 min @ 15m: 1*60*(15/10 + 1) = 150L
Extended safety stop 5 min at 5m (1.5 ATA): 5*60*(5/10 + 1) = 450L
Min gas including deep stop and extended safety stop: 240L + 450L + 150L + 450L = 1290L, 1290/12 =108 bar in a 12L, round to 110 bar
As a novice diver, how do you determine reasonable numbers for a rock bottom calculation?
As a novice diver you should, IMO, use the same approach that I used: Determine your actual gas consumption rate, use stock numbers for ascent rate and safety stop depth/duration and do the math. Just as the min gas/rock bottom procedure tells you to do. It's a lot better than "surface with 50 bar, but only God knows how I'm gonna do that", and the numbers can be adjusted as you gain experience and find out if the stock numbers are appropriate for your diving and you can make an educated decision on your personal need for conservatism. Easy peasy, right?
And, unlike "surface with 50 bar, but only God knows how I'm gonna do that" or the woefully misleading "50 bar plus 10 bar / 10m" so-called rule which
Foxfish has been plugging, you can
tailor your min gas calculations to fit your own diving. Not bad, eh?