PSI or BAR in Tech diving?

[Blackwood]

Since you're the OP I don't feel bad about participating in this hijack

Take this vplanner screenshot for example.

Stop at 9m 6:00 (53)
Stop at 6m 8:00 (61)

If the ascent schedule wanted me to spend the full 6:00 at 53 and add the ascent time in, then the runtime after 8:00 at 6m wouldn't be 61. It would be 61 + however long it took me to get from 9m to 6m, and from 12m to 9m, and from 15m to 12m, and so on. Right?




As for how I run my dives... I and most of my teammates use Ratio Deco. So let's say I have a deco schedule that (ignoring deep stops for simplicity) reads: 70 for 4, 60 for 4, 50 for 2, 40 for 2, 30 for 3, 20 for 10, 10 for 5 (typical for a 30 minute dive to 150 feet).

We'll hit 70 feet and signal switch. Once everyone is on deco gas, deco time starts. At 3:30, into the stop, the captain signals to level up. Ideally, we hit 60 feet at the 4 minute mark. If we're fast, we'll wait to start the clock until 4. If we're slow, we'll eat the time. Now, 3:30 into the 60 foot stop, we start moving again. And so on to the surface, except I tend to spend the full time at the last stop (e.g. I won't start my final ascent at 4:30 into the 10 foot stop in this example).

We have our own idiosyncrasies with the shallow stops. I tend to like that 10 foot stop. Others like to spend the whole oxygen segment at 20 and finish off with a 6-minute ascent from there. Shrug.

 

[Ste Wart]

No worries about the hijack.

OK. Yes I'm seeing where you're running with this.

However have you tried putting V-planner into 30 sec increments?

All the training I've gone with is 'you don't move until you see the time' (assuming that you're on schedule). Then with hitting stops it is agreed that 15secs+/- on stops doesn't matter. So I travel as the clock changes, aiming for 20 sec/3m climb. So for any given stop I spend 20 secs less there than is indicated.

As regards Ratio Deco. Not a subject I want to touch on as that would really hijack the thread

 

[Blackwood]

Haha no doubt.

But it makes little difference. I'd dive a Vplanner or decoplanner schedule the same way.

(edit - no I've not put Vplanner into 30 second increments. Does it make a difference to how it sums runtime?)

 

[fdog]

Marc, I absolutely understand what you're saying, since overall segment time is my strategy as well...

However, I'll admit I have a pea brain, and when I'm calling the deco, I find it easier to move on the clock. Come to think, so do my team mates.

Still, either way works for me. I'd be happy to follow your shape just as well as moving on the clock. It's all an approximation anyway.


All the best, James

 

[Colliam7]

. . .all the divers were using Imperial to plan their dives and I was not. All my training has been done in Europe and Egypt when it comes to tech, so therefore I'm Metric all the way. I looked at them as if they just suggested I kiss my sister when they asked me my SAC rate in Imperial. It's never really occurred to me to even know what it would be. . . . I feel personally that Metric and Tech go hand in hand, for several reasons. . . .
How does everyone else feel on this subject?

I really do NOT think it matters, at all. It makes sense to you because that is how you trained. An argument that exclusively favors one system over the other is hard to sustain on a intellectual basis. What DOES matter is that all members of the team are singing from the same page of the songbook - all are using imperial, or all are using metric. I trained in imperial, I use imperial, and I know how to use it. But, if I have gauges calibrated in metric. and run tables created in metric nomenclature, and a team that ALL want to use metric, I can adapt. Putting aside the fact that I don't usually have a need to dive with a team that uses metric measurements, I wouldn't have a problem with that, as long as 1) we ARE ALL using the same run times and units of measurement, and 2) we are all using gauges with the same units of measurement. Likewise, I also don't care if the temperature is reported in Celsius or Fahrenheit, as long as we agree on what we are using BEFORE we start a dive.

 

[TSandM]

If you guys have done dissimilar tank matching between metric and Imperial divers, how do you do it? I honestly don't have a clue what an LP95 is in metric terms, or what a 15L tank is in imperial.

 

[Blackwood]

Do the math, Lynne. I have a spreadsheet somewhere at home I can try to dig up and send you later, but just divide rated volume by rated pressure (CF/PSI), them multiply by 14.7PSI/ATM (CF/ATM), then multiply by 28.3L/CF (L/ATM which is close enough to L/BAR).

Example, a HP100:

100CF/3442PSI = .03CF/PSI.
.03CF/PSI (14.7PSI/ATM) = .44CF/ATM. This is the internal volume of your cylinder, more-or-less.

.44CF/ATM (28.3L/CF) = 12.5L/ATM.

So a HP100 is roughly a 12L cylinder.

 

[Kern]

If you guys have done dissimilar tank matching between metric and Imperial divers, how do you do it? I honestly don't have a clue what an LP95 is in metric terms, or what a 15L tank is in imperial.

If the 15lt is a steel tank it will 232 bar or 300 bar. More than likely it'll be 232 bar, but it will have the WP stamped on the tank anyway, along with the WC. Using underwater maths, 15lt X 232 bar is about 3500lt. There's about 30lt to 1cft. So its about 120cft. There's about 15psi to a bar. Go from there. Close enough for gobament work anyway.

Is your 95cft tank really 95cft. Beats me. Whats it's working pressure. Beats me, but there seem to be untold variations to choose from.

 

[TSandM]

Well, none of this is math I'm going to be real excited about doing while floating in the cenote before submerging . . . I'm sure glad I'm a MX cave diver, where the Al80 rules!

 

[rjack321]

Like Marc my buddies and I deco on runtime not stop time. If you are scootering up slope and it takes 6mins to get from 21m/70ft to 18m/60ft as far as I'm concerned the 5min "18m/60ft" stop is done and we keep going up to 15m/50ft.

I have about 12 gauges in psi along with an imperial bottom timer and don't see any need to change them. I probably won't unless all my buddies decide to as well.