Communicating remaining pressure on doubles(twinset)

[EFX]

A set of double tanks filled to 3000psi doesn't equal 6000psi, it will still be 3000psi. For simplicity, the example assumed everyone has the same SAC rate so weight/trim isn't relevant. Everyone starts with 3000psi. The single-tank divers consumed 2/3 of a their tank, ending with 1/3 reserve (1000psi). A doubles diver that consumed the same volume of gas would have consumed 1/3 of their starting volume, leaving 2/3 remaining (2000psi).

It perhaps is better understood by looking at this by total volume. Let's say one tank is 90cubic feet:

	Single-tank	Doubles
Dive 1 Start	90	180
Dive 1 End (60cf consumed)	30	120
Dive 2 Start	90	120
Dive 2 End	30	60

I misunderstood your original post. The two tanks are in parallel so given the same SAC rate you had more gas left than they did even though your tank pressure was less than yours. I still stand by what I said earlier, i.e. don't lie about remaining pressure. I agree with what others said that it is imperative you explain to the DM you are on doubles and therefore will have more gas than the others at the same or lower tank pressure.

 

[boulderjohn]

You could have just stopped there. That alone means it would be impossible for you to burn through your gas. Impossible! Simple minded DM.....how dare he.

No, I shouldn't have answered at all. I should have realized your only purpose in posting was to take a nasty and unprovoked cheap shot at me, and I should have ignored you, as I will now.

 

[MidOH]

I signal some jibberish, then an "ok" sign.

Generally, after signaling "trouble with my nipples, ok.", twice on day1, they leave me alone.

It's very rare that a DM mentions their psi signals in the brief. 2 fingers up, followed by 5 sideways, is 2500 over here. Then followed by "ok" cause I've got enough to complete the plan. I get some amusement watching others desperately trying to signal pressure, when they have no clue.

....and then you have guys with indys, guys with ponys....

If the DM sticks to the dive plan, [1 hour underwater], there's no worries for any of us. We can guage our own use. Should worry about single tanks more.

Even air hogs on doubles have an advantage nearly always, to single tank divers. My sister is way easier on air consumption, but she's not going to ever surface after me on dive 2, if I'm using doubles.


On another note: I'll admit. It is getting old. Stopping to signal air pressure, on a simple single tank shallow al80 dive.



If we're sweating about surfacing, not as one group, due to current, drift,..... bring moar air.

I wish rec boats had Al40 stages on board for bigger guys.

 

[tursiops]

I talk it over with the dive guide. What has usually been the case for most day-trip insta-buddy (same-ocean-buddy/) dives is:

I signal my usable gas remaining. Diving sidemount I add up both pressure readings, and subtract 500 psi (instead of surfacing with a minimum of 500 in one tank, I have to have 500 in each tank). At the beginning of a dive starting with 3250 in each tank, I'd be signaling 6000. Towards the end of the first dive with 2000 and 2200 remaining, I signal 3700. Toward the end of the second dive, with 1300 and 1000, I signal 1800.

For doubles, I'd do the same, but instead of adding two gauges, simply double your pressure and subtract 500.

At least this way the remaining air message remains consistent among all divers.

That's a terrible idea. All should simply respond with wear their gauges say, and not be forced to do math underwater.

 

[tursiops]

2 fingers up, followed by 5 sideways, is 2500 over here

I've never heard that or seen that in almost 6 decades of diving and guiding, all over the world.

 

[MidOH]

Which is why it could be handy to go over that in the brief.


In his vid, we just signal the 1st two digits. 3270 just gets rounded up to " three-three", or down to "three-two".



But the twin tank math does make sense. Each tank at 1500, signal 3000.


Give the DM a simple guesstimate of your air remaining, instead of each tank.

 

[tursiops]

Which is why it could be handy to go over that in the brief.


In his vid, we just signal the 1st two digits. 3270 just gets rounded up to " three-three", or down to "three-two".



But the twin tank math does make sense. Each tank at 1500, signal 3000.


Give the DM a simple guesstimate of your air remaining, instead of each tank.

Why are you showing that video, which is NOT showing 5 fingers horizontal, by the way. In fact, he us not even showing the standard tech hand signs.

 

[boulderjohn]

Horizontal v. upright finger signals

Since the idea of upright v. horizontal fingers for numbers was brought up, I will explain to those not trained in advanced techniques that the difference is commonly used in advanced diving. The idea is to be able to communicate numbers in an environment when signals need to be made by one hand.

Fingers upright = numbers 1-5
Fingers horizontal = numbers 6-9

If you decide that horizontal fingers mean something different, you will confuse people trained this way.

 

[MidOH]

Because people always mess up 5.

5 is 5. Sideways or vertical

 

[tursiops]

Because people always mess up 5.

5 is 5. Sideways or vertical

No.