PSI or BAR in Tech diving?

[Cap335]

The only reason it would matter is gas planning/matching. If you don't want to bother with the math use a computer and just switch between metric and imperial. Other than that let everyone use what they are used to thinking in.

Randy

 

[liuk3]

The only reason it would matter is gas planning/matching.

That's a pretty big component since I'm planning my dive with my buddies before dives. I also wouldn't say it's just gas planning, rather it's planning the entire dive in general including (multi-level) dive plan, deco profile, and contingency planning.

 

[TSandM]

When I did my Cave 1 class, we had one student from Norway and two of us from the US. The instructor made us alternate our dives in metric and Imperial, so we all got facile using both sets of units. As we were all using Al80 tanks, though, we did not have to do gas matching calculations. I'm pretty good with depth and pressure, but trying to figure out who has the highest gas consumption between cf/m and l/m would baffle me.

 

[explorer08]

Yesterday evening I read a bit in the German version of the TDI 'Advanced Trimix' manual by Steve Lewis. In the chapter about gasmanagement there is an authors remark. It means: If there is any argument for using the metric system to make planing of technical dives easier, the calculation of gas volumes would be the best.

 

[Ste Wart]

Great interesting stuff going on.

couple of extras.

The Imperials on my dives all had extra deco, nothing big, but just an extra minute or 2.

3m stops. Lets break this down. On a 1 minute stop I know that I want to spend roughly 30-40secs at the actual depth, after travel time. So I can break that into 5 secs per metre in real terms.
Later on the deco, when I really want to slow it down I can take 1 whole minute to the next level, ergo 20 secs per meter or 2 secs per 10cm. This seems easier to break down for me.

 

[Blackwood]

We tend to move 30 seconds before the stop ends, arriving at the next depth level more or less on the clock.

I can spend a whole minute moving as well, and calling it 3mpm rather than 10fpm doesn't change anything.

It's all what you're used to. Given my profession (which involves a wide variety of unit systems and units within each system), I tend to give heavy import to the principles themselves and not get caught up in what units I'm using. Meters, mm, km, inches, mils, microns, kgs, lbm, N, lbf, radians, degrees, kips, GPA, joules milliwatts... whatever. I'll convert.

P.s. - fix your math (20 sec / m doesn't equal 2 sec / 10 m).

 

[Ste Wart]

We tend to move 30 seconds before the stop ends, arriving at the next depth level more or less on the clock.

I've never heard that one before.

I move on the clock. Surely you're shaving stops if you move before the time?

 

[Blackwood]

I've never heard that one before.

I move on the clock. Surely you're shaving stops if you move before the time?

I don't believe that actually spending the full 6 minutes at 70 feet really matters much (those even increments just make for a simple output from the algorithm). It's total time in the general vicinity. I consider deco stops in levels. 120 to 110 is a level. 70 to 60 is a level. If I spend 5:30 at 70 feet and 0:30 at 65 (aka the ascent), I call that at 6 at the 70 foot level.

Since the ascent schedules that I'm used to don't add leveling up to the total runtime (example), I wouldn't say I'm shaving deco. Rather, if I spent 6:00 at 70, took 30 seconds to move, and then started the clock for my 60 foot stop, I'd say I'm adding to the deco. Which is fine too.

 

[AndyNZ]

If you are talking about pressure, it doesn't make any difference. All my battlefield calcs that I am doing in my head are just as easily done using PSI as they are bar.

If you are talking about depth, it makes no difference either - apart from exception noted below.

Gas volumes is the only area where metric makes things easier. Tank factors get around that, though personally I feel it's a "clunky" solution. But how often do you really worry about volume? That's mostly a pre-dive issue as opposed to an on-the-fly calculation.

I've dived mixed teams using imperial and metric. Signalling and communication is the only real issue - for example, on deco I know that a few imperial devotees signal the next stop depth on an ascent, i.e. "go up to 20ft". Which is a little confusing at first when you are sat at 10m and someone is saying to go up to 20. It's easier to just drop that out and do a generic "go up to the next stop".

 

[Ste Wart]

Since the ascent schedules that I'm used to don't add leveling up to the total runtime, I wouldn't say I'm shaving deco. Rather, if I spent 6:00 at 70, took 30 seconds to move, and then started the clock for my 60 foot stop, I'd say I'm adding to the deco. Which is fine too.

Which program are you using?

I'm confused. You're not running your schedule? You're restarting your timer at each depth and then basing your time from there. So yes you are adding to your deco, but why?
Occasionally a few of my dive buddies like to run a slower ascent in the last few stops (1 minute per 3 m) which adds to your run time. I prefer to just add in a a few deep stops (which increases my deco anyway: buhlmann) and then do an extra 5-10 minutes at the last stop for conservatism.
How do you run your schedules?