Communicating remaining pressure on doubles(twinset)

[lostsheep]

4 cylinders for 2 NDL dives is asinine.

I would ASSume most people diving doubles have gotten to the point where they can relax and SAC rate has dropped lower than the average single tank diver who needs a DM.

EDIT: you seemed to imply doubles with your overweighted claim, perhaps something was lost in translation

 

[inquis]

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

I'll assume you mean a pair of baby doubles, otherwise your previous objection to excessive gas weight would be present. That's certainly an option, but logistics of boat storage and availability during travel make that less attractive than it would initially seem.

 

[diver-man]

I'll assume you mean a pair of baby doubles, otherwise your previous objection to excessive gas weight would be present. That's certainly an option, but logistics of boat storage and availability during travel make that less attractive than it would initially seem.

Yes. Net weight difference of a full D8.5 vs full D12 at 232 Bar is about 10 kg. That's a lot.

 

[rjack321]

Plenty of people around here to a 30m dive and a 20m dive on one set of double 100s (232bar ~D12). The singles might be in the shop or they just want to dive their doubles, its really not a big deal. Finding an actual charter nowadays is a much bigger challenge.

 

[inquis]

Yes. Net weight difference of a full D8.5 vs full D12 at 232 Bar is about 10 kg. That's a lot.

I was speaking of the buoyancy difference, not weight, as that is what might be difficult underwater. Even a double D12 is only 3.6 kg more negatively buoyant (*) at the beginning of Dive 1. That isn't terribly troublesome to deal with and becomes easier as gas is used.

As far as weight (out of the water), that's again a personal call whether it is manageable.

Really, though, I'm just pushing back on your blanket statement. Like most configuration choices, there are pros & cons. It may be "full stop" for you but not for someone else with different priorities/strength/skills.


(*) Certainly, I am assuming neutral buoyancy is achievable with no gas present & empty wing in each case. In other words, adding another cylinder & bands/manifold means you can remove lead or other form of ballast. If that's not the case, that's a pretty big "con" that should be considered.

 

[Wallowa]

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

Same here....6 decades also and all the gestures only create confusion, entirely unnecessary; DM is not your mother, if needed let them read your SPG or hold your hand...as for doubles vs single bottle...personal choice and responsibility.. each diver is responsible and accountable for their own safety, a concept seemly lost in current push for co-dependent diving...your returning to surface safely is entirely up to your judgment and decisions....like it or not diving is always in the end a solo event.

Hey I could be wrong... Make your own choices.

 

[diver-man]

I was speaking of the buoyancy difference, not weight, as that is what might be difficult underwater. Even a double D12 is only 3.6 kg more negatively buoyant (*) at the beginning of Dive 1. That isn't terribly troublesome to deal with and becomes easier as gas is used.

As far as weight (out of the water), that's again a personal call whether it is manageable.

Really, though, I'm just pushing back on your blanket statement. Like most configuration choices, there are pros & cons. It may be "full stop" for you but not for someone else with different priorities/strength/skills.


(*) Certainly, I am assuming neutral buoyancy is achievable with no gas present & empty wing in each case. In other words, adding another cylinder & bands/manifold means you can remove lead or other form of ballast. If that's not the case, that's a pretty big "con" that should be considered.

My general rule of thumb: use right cylinder(s) for the dive. So if the dive is suitable for D8.5 then use D8.5 and not D12 just because you plan another dive that day.

Instead, fill or swap cylinder(s) between dives.

You have to compare full D12 to full D8.5 and not full D12 to half-empty D12.

 

[lostsheep]

My general rule of thumb: use right cylinder(s) for the dive. So if the dive is suitable for D8.5 then use D8.5 and not D12 just because you plan another dive that day.

Instead, fill or swap cylinder(s) between dives.

You have to compare full D12 to full D8.5 and not full D12 to half-empty D12.

What you propose is not feasible everywhere.

Not all dive boats have compressors, even fewer have nitrox capabilities

Very few boats have room for people to bring 2 sets of doubles.

Tiny doubles aren’t common around here anyways. I’ll admit I may have 2 sets myself but I have tank hoarding issues.

Double 80s/85s is not grossly overweighted if dived correctly.

Full go

 

[TylerG.]

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.

This is hands down the biggest abomination of a gas plan I have ever seen.