Rule of 1/3s and different tank sizes

[Kevrumbo]

The higher SAC will determine who hits thirds first, but is irrelevant to calculating turn pressures.

SAC Rates are in fact directly proportional to the gas volume consumed of each diver, and will determine who reaches team turn volume first. So to claim "Regardless of SAC", or that "SAC Rates don't matter, are irrelevant, or not needed" is misleading and incorrect, even though it apparently seems extraneous & abstract to calculating Turn Volumes/Turn Pressures in LimitingThird's. . .

 

[CptTightPants21]

SAC Rates are in fact directly proportional to the gas volume consumed of each diver, and will determine who reaches team turn volume first. So to claim "Regardless of SAC", or that "SAC Rates don't matter, are irrelevant, or not needed" is misleading and incorrect, even though it apparently seems extraneous & abstract to calculating Turn Volumes/Turn Pressures in LimitingThird's. . .

We are all talking about the same thing; let's not get hung up on semantics. Victoramara has clarified his statement adequately.

 

[Doby45]

We are all talking about the same thing; let's not get hung up on semantics. Victoramara has clarified his statement adequately.

Spoken for truth, just damn. It seems like you have some people that just really like to dive and then you have some people that just really love the planning of the dive. The whole "Can't see the trees for the forest" thing.

 

[Kevrumbo]

We are all talking about the same thing; let's not get hung up on semantics. . .

Not understanding "semantics" and proper gas planning will get you drowned. . .

If you have someone on the team with a very large SAC Rate -say 3 times yours or greater- and with dissimilar tanks, then it would be a good idea to check the turn volume, turnaround elapsed time and each teammate's turn pressure numbers to ensure the reserve volume is sufficient to support them out of the cave in a gas share contingency. Don't just blindly apply Third's and expect the calculation to be correct and true for all having enough reserve to control the Turnaround Point . . .

Example:
Limiting Third's Gas Plan.

Diver A:
0.3 cf/m Sac Rate with double AL50's at 3000psi.

Diver B:
1.2 cf/m Sac Rate with double hp133's at 3500psi.

Diver A has smallest total volume of backgas at 100cf so we take Thirds of this which is 33cf (the Team Turn Volume);

Diver B uses this 33cf to figure his consumed delta pressure at 434psi. His SPG turn pressure is 3500psi minus this 434psi, and he calls for the dive turnaround at 30fsw (1.9ata) depth after ~14min cave penetration elapsed time.

In that 14min, Diver A uses: 0.3 cf/m x 1.9ata x 14min = 8 cf;
and Diver B uses: 1.2cf/m x 1.9ata x 14min = 32 cf.

So for the penetration, Diver A uses 8 cf and Diver B uses 32 cf.

If Diver A or Diver B loses all his gas at the turnaround, the donating diver needs a combined sum of 8 cf and 32 cf to exit the overhead (40 cf).

Check if Volume Reserves at Turnaround are enough:
Diver A uses 8 cf out of his 100cf supply, and has remaining 92 cf;
Diver B uses 32 cf out of his 266cf supply, and has remaining 234 cf.

So the answer is yes - that both teammates have enough Reserve Gas to cover, even Diver A in this extreme inequality of Sac rates and dissimilar tanks.
-------------

--->What happens if Diver A mistakenly thinks he controls the turnaround with Third's?

He consumes the same team volume 33 cf and calls for the turnaround at ~57min with a SPG reading of 2000psi at 30fsw (1.9ata) depth.

In that 57min, Diver A uses: 0.3 cf/m x 1.9ata x 57min = 32 cf;
and Diver B uses: 1.2cf/m x 1.9ata x 57min = 130 cf.

So for the penetration, Diver A uses 32 cf and Diver B uses 130 cf.

If Diver A or Diver B loses all his gas at the turnaround, the donating diver needs a combined sum of 32 cf and 130 cf to exit the overhead (162 cf).

Check if Volume Reserves at Turnaround are enough:
Diver A uses 32 cf out of his 100 cf supply, and has remaining 68 cf;
Diver B uses 130 cf out of his 266 cf supply, and has remaining 136 cf.

So in this case the answer is No -they will go Out-of-Gas inside the cave, because Diver A mistakenly thought he determined the Third's Turnaround at 57min.

The point is again:

SAC Rates are in fact directly proportional to the gas volume consumed of each diver, and will determine who reaches team turn volume first. So to claim "Regardless of SAC", or that "SAC Rates don't matter, are irrelevant, or not needed" is misleading and incorrect -You must also know which diver controls the Turnaround, and that diver has to be the one with Highest SAC Rate.

 

[steady1570]

And some people say rebreathers are complicated and will get you killed.... long live the Imperial measurement system and SAC calculations.... [/JOKE]

-Mark

 

[Kevrumbo]

And some people say rebreathers are complicated and will get you killed.... long live the Imperial measurement system and SAC calculations.... [/JOKE]

-Mark

OMG, it works for the rest of the World's unit system too! ;-)

Diver A:
4 l/min Sac Rate with double AL40's (11 l/bar) at 200bar.

Diver B:
28 l/min Sac Rate with double hp190's (36 l/bar) at 300bar.

Diver A has smallest total volume of backgas at 2200 liters so we take Third's of this which is 733 liters (the Team Turn Volume);

Diver B uses this 733 l to figure his consumed delta pressure at 20bar. His SPG turn pressure is 300bar minus this 20bar, and he calls for the dive turnaround at 9 meters (1.9ata) depth after ~14min cave penetration elapsed time.

In that 14min,
Diver A uses: 4 l/min x 1.9ata x 14min = 106 liters;
and Diver B uses: 28 l/min x 1.9ata x 14min = 745 liters.

So for the penetration, Diver A uses 106 l and Diver B uses 745 l.

If Diver A or Diver B loses all his gas at the turnaround, the donating diver needs a combined sum of 106 l and 745 l to exit the overhead (851 liters).

Check if Volume Reserves at Turnaround are enough:
Diver A uses 106 l out of his 2200 l supply, and has remaining 2094 liters;
Diver B uses 745 l out of his 10800 l supply, and has remaining 10055 liters.

So the answer is yes - that both teammates have enough Reserve Gas to cover, even Diver A in this extreme inequality of Sac rates and dissimilar tanks.
-------------

--->What happens if Diver A mistakenly thinks he controls the turnaround with Third's?

He consumes the same team volume 733 l and calls for the turnaround at ~96min with a SPG reading of 133bar at 9 meters (1.9ata) depth.

In that 96min,
Diver A uses: 4 l/min x 1.9ata x 96min = 730 liters;
and Diver B uses: 28 l/min x 1.9ata x 96min = 5107 liters.

So for the penetration, Diver A uses 730 l and Diver B uses 5107 l.

If Diver A or Diver B loses all his gas at the turnaround, the donating diver needs a combined sum of 730 l and 5107 l to exit the overhead (5837 liters).

Check if Volume Reserves at Turnaround are enough:
Diver A uses 730 l out of his 2200 l supply, and has remaining 1470 liters;
Diver B uses 5107 l out of his 10800 l supply, and has remaining 5693 liters.

So in this case the answer is No -they will go Out-of-Gas inside the cave, because Diver A mistakenly thought he determined the Third's Turnaround at 96min.

The point is again:

SAC Rates are in fact directly proportional to the gas volume consumed of each diver, and will determine who reaches team turn volume first. So to claim "Regardless of SAC", or that "SAC Rates don't matter, are irrelevant, or not needed" is misleading and incorrect -You must also know which diver controls the Turnaround, and that diver has to be the one with Highest SAC Rate.