Communicating remaining pressure on doubles(twinset)

[MidOH]

Can't figure it out?

Somebody just signaled 3 up, 5 sideways.

What psi are they at?

 

[scubadada]

When everyone is diving an AL80 on a liveaboard or a land-based charter dive, asking for a pressure would seem to make some sense. When divers have disparate cylinders, including doubles, asking for a pressure seems ridiculous. It's your consumption rate and volume of gas left.

 

[tursiops]

Can't figure it out?

Somebody just signaled 3 up, 5 sideways.

What psi are they at?

I can only guess. That's not good enough.

 

[EFX]

I watched the video on hand signals. One handed signals is what I use and I've had mixed success in teaching my buddies to adapt them. Alas, old habits die hard. Cave divers use one-handed signals because frequently the other hand is occupied. The instructor in the video is using a variation of what's taught in the NACD book of hand signals for communicating tank pressure. He adds a signal for 10 which is not in the book. I don't know why it is needed and he didn't explain why. Personally, I just give the first two numbers for tank pressure. With 1350 psi show 1 then 3. For 850 psi show 8 then 5.

 

[jadairiii]

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.

The purpose, and I hope some got it, was to show that none of us are above the "rules". It was a recreational dive, DM had a job to do, check everyone's gas. When he got to you, rather than the "WTF" moment and wasting his time pointing out all your tanks , why not just tell him what you had in back-gas and move on. Make the DM's job as simple as possible. And let the DM focus on the rec divers.

So, it was not a "nasty and unprovoked cheap shot" at you. It was a learning moment for others (and maybe you).

 

[diver-man]

It is a false economy to carry one air for two dives. It just means that for the dive no. 1 you are overweight with all consequences, plus dive planning is a crap.

Do you want to make two dives on a single trip? Carey on another cylinder and swap it between dives. Full stop.

 

[lostsheep]

It is a false economy to carry one air for two dives. It just means that for the dive no. 1 you are overweight with all consequences, plus dive planning is a crap.

Do you want to make two dives on a single trip? Carey on another cylinder and swap it between dives. Full stop.

Nonsense. Complete and utter bs.

I’ll take my doubles on a 2 dive NDL charter over 2 singles everytime. I hate swapping tanks and I like redundancy. I am not so overweighted I can’t swim them up and I have redundant buoyancy.

Full go

 

[rjack321]

Let's say you are doing a 2-tank dive on doubles with a group where some are on singles and some (or only you) are on doubles, so you have the benefit of not needing swap tanks between dives. During the 2nd dive, if the leader/guide does a pressure check, how would you convey your remaining gas? Because if you signal what's on your SPG/AI-computer, there is the possibility it is interpreted as having significantly less gas (volume) than you actually do. While of course a good leader/guide should be able to differentiate between single and double pressures, and this all should be addressed pre-dive, it may not always be the case when there may be a lot going on and to keep track of.

Example scenario: everyone is diving same volume tanks and have the same SAC rate. You ended the first dive with 2000psi/140bar in your doubles. So you start your second dive with that much, and those on full singles start with 3000psi/205bar. After a while, the leader/guide does a pressure check all around. At this point, you and everyone has consumed the same volume of gas. Whereas your gauge may show 1250psi/85 bar, theirs will be at 1500psi/103 bar. Because of the reserve gas from the first dive you're carrying over, the two pressures are not drastically different such that the leader/guide may not to think beyond the erroneous conclusion that you are consuming gas very fast and remainder of the dive may need to be altered or ended much sooner.

Would you just go ahead and signal your remaining pressure and risk ending the dive ~20 minutes sooner? Could you signal twice your PSI to maintain semi-parity with those on singles?

1) The group should go over tank sizes and starting pressures before the dive starts.
In a mixed group of folks in singles, doubles, LP, HP, etc everyone will have different starting, turn, and ending pressures. It's up to the DM to know this, this is their job.

2) Just signal your remaining pressure. The fact you are in doubles is WAY more obvious and easy to remember for the DM than one diver is in a single 80, another in an lp85, another in a 119 and another is a 130. There is no need to second guess doing some math in your head on the DM's behalf. They ask for pressure then report back pressure.

 

[diver-man]

Nonsense. Complete and utter bs.

I’ll take my doubles on a 2 dive NDL charter over 2 singles everytime. I hate swapping tanks and I like redundancy. I am not so overweighted I can’t swim them up and I have redundant buoyancy.

Full go

Where did I say "singles"?

Do you want to make two dives with a twinset? Take a pair of twinsets with you!

 

[inquis]

for the dive no. 1 you are overweight with all consequences

That's certainly a potential disadvantage, but one that can be overcome with skill.

The advantage is redundant air, which could be very useful when current, visibility, and/or buddy inattentiveness make a single source of air a risky choice.

Skills, priorities, and risk tolerance are all going to be personal calls.