TDI intro to tech review

[Kevrumbo]

What did your nominal volume SAC/RMV rate turn out to be with the D12 liter steel cylinders?

Is it in the "magic range" of 15 to 17 liters/min, or better?

Why is that range considered "magic"?

18 - 19 on most of my dives with drysuit and all gear. Need to drop it a little bit.

That's ok and good for now for a nominal value, and it still works the magic range. . .

I call it the "magic RMV range", because whatever your depth is in meters, you will end up consuming at most that value in ten minutes in bar pressure units -so for example, if you're at 30msw depth, you will consume approximately 30bar in ten minutes. Or if you're at 45msw for ten minutes, you will consume 45bar; or if at 60msw for ten minutes, you will consume 60bar etc.

Try it on your next dive -go to a relatively shallow depth like 20msw with your double 12L cylinders with nominal breathing floating non-exertion buoyancy & finning, and see if you use up approx 20bar in ten minutes (or alternatively with a single 12L tank, see if you consume 20bar in five minutes at 20msw).

Can you derive from your RMV of 19 liters/min per ATA, and show the maths that make this pressure SAC rate and ATA depth relationship work?

 

[DanielRJones]

That's ok and good for now for a nominal value, and it still works the magic range. . .

I call it the "magic RMV range", because whatever your depth is in meters, you will end up consuming at most that value in ten minutes in bar pressure units -so for example, if you're at 30msw depth, you will consume approximately 30bar in ten minutes. Or if you're at 45msw for ten minutes, you will consume 45bar; or if at 60msw for ten minutes, you will consume 60bar etc.

Try it on your next dive -go to a relatively shallow depth like 20msw with your double 12L cylinders with nominal breathing floating non-exertion buoyancy & finning, and see if you use up approx 20bar in ten minutes (or alternatively with a single 12L tank, see if you consume 20bar in five minutes at 20msw).

Can you derive from your RMV of 19 liters/min per ATA, and show the maths that make this pressure SAC rate and ATA depth relationship work?

At 30m mine works out at 32bar at 40m its 39bar below 30 it falls away a bit more with 14bar at 10m

 

[EireDiver606]

Out of curiosity how much did the course cost? Or I’d it different everywhere you go?

Sounds very similar to GUE Fundamentals but we didn’t use stages and deco

 

[stuartv]

I call it the "magic RMV range", because whatever your depth is in meters, you will end up consuming at most that value in ten minutes in bar pressure units

Thanks for the explanation.

 

[Kevrumbo]

Thanks for the explanation.

Try it @stuartv -switch your Perdix AI to Metric and see if it also works in your case as well: ten minutes at metric depth 20msw for example is approx how much in you'll consume in bar (i.e. 20 bar) using a set of manifolded BM doubles (D12's to D15's); or in five minutes using a single tank of 12L to 15L cylinder size.

 

[DanielRJones]

Out of curiosity how much did the course cost? Or I’d it different everywhere you go?

Sounds very similar to GUE Fundamentals but we didn’t use stages and deco

£180

 

[RainPilot]

call it the "magic RMV range", because whatever your depth is in meters, you will end up consuming at most that value in ten minutes in bar pressure units

Surely that will be tank dependent to a great extent?

Quick maffs:
15 litres/min on a single 15L tank at 20m for 10 minutes is (15 x 3ATA x 10min= 450 litres thus 30 bar)
Same RMV on twin 15L will be 15 bar for same
Twin 20 L tanks will be 11.25 bar

Bearing in mind the "at most" part, we would be looking at 20 bar in ten minutes, so any tank smaller than 22.5L total volume would not meet the "rule". This is basically a double 80 setup. A lot of people dive smaller tanks especially in Europe. I dive twin 7L 300 bars as well as twin 8.5L 232 bar sets when in a drysuit.

For my small set, I would be using 32 bar every ten minutes at 20m at 15 l/min.

 

[DanielRJones]

Surely that will be tank dependent to a great extent?

Quick maffs:
15 litres/min on a single 15L tank at 20m for 10 minutes is (15 x 3ATA x 10min= 450 litres thus 30 bar)
Same RMV on twin 15L will be 15 bar for same
Twin 20 L tanks will be 11.25 bar

Bearing in mind the "at most" part, we would be looking at 20 bar in ten minutes, so any tank smaller than 22.5L total volume would not meet the "rule". This is basically a double 80 setup. A lot of people dive smaller tanks especially in Europe. I dive twin 7L 300 bars as well as twin 8.5L 232 bar sets when in a drysuit.

For my small set, I would be using 32 bar every ten minutes at 20m at 15 l/min.

He was talking aboit twin 12s. Where it works but yes twin 10s and below it does not work the best

 

[RainPilot]

He was talking aboit twin 12s. Where it works but yes twin 10s and below it does not work the best

Makes sense, it didn't come across clearly to me so I was making sure that people coming here later don't walk away with the wrong idea that that RMV is "magic" all the time.

 

[taimen]

Can't beat wireless AI for logging and analysing how much your SAC/RMV really was during different phases of the dive. It is amazing how much you can breath during more complex drills.

Your course sounds really nice!