I was certified OW and Advanced twenty years and did about 30 dives but then stopped diving. I am starting back again and have projects to do a GUE Fundamental Skills course very soon.
I downloaded the course materiel and started doing the gas management exercices. I have been doing a lot of supplementary reading also. Comparing the Metric and Imperial systems, it appears the Metric is much more simple and intuitive for all aspects of dive planning.
I am thinking of going Full Metric and for instance buying a SPG that reads in Bars instead of PSI.
I live in Montreal, Quebec, Canada, and I realize that probably most potential buddies around me will still be using the Imperial system.
Any thoughts and comments about me taking this route ?
Below are some example pressure Surface Consumption Rate (SCR) values for a variety of common cylinders with an arbitrary volume SCR (also known as volume SAC rate or RMV):
Given a arbitrary nominal volume SCR of 22 liters/min per ATA (
that's 0.78 cuft/min per ATA in US Imperial Units, a reasonable & achievable volume SCR for most novice divers, and exercise level for fit advanced divers with sustained active finning):
Cylinder Size | Pressure SCR
11L/bar tank (AL80):
2bar/min per ATA;
12L/bar tank (Steel HP100): 1.8bar/min per ATA;
13L/bar tank (AL100): 1.7bar/min per ATA;
15L/bar tank (Steel HP119): 1.5bar/min per ATA;
16L/bar tank (Steel HP130): 1.4bar/min per ATA;
11L Twins (Double AL80's):
1bar/min per ATA;
12L Twins (Double HP100's): 0.9bar/min per ATA;
16L Twins (Double HP130's): 0.7bar/min per ATA.
Given a arbitrary nominal volume SCR of 15 liters/min per ATA (
0.53 cuft/min per ATA in US Imperial Units, relaxed with minimal finning for advanced divers):
11L/bar tank (AL80): 1.4bar/min per ATA;
12L/bar tank (Steel HP100): 1.3bar/min per ATA;
13L/bar tank (AL100): 1.2bar/min per ATA;
15L/bar tank (Steel HP119):
1bar/min per ATA;
16L/bar tank (Steel HP130): 0.9bar/min per ATA;
11L Twins (Double AL80's): 0.7bar/min per ATA;
12L Twins (Double HP100's): 0.6bar/min per ATA;
16L Twins (Double HP130's): 0.5bar/min per ATA.
Given a arbitrary nominal volume SCR of 11 liters/min per ATA (
0.39 cuft/min per ATA in US Imperial Units, drift diving floating neutrally buoyant & going with the current):
11L/bar tank (AL80):
1bar/min per ATA;
12L/bar tank (Steel HP100): 0.9bar/min per ATA;
13L/bar tank (AL100): 0.8bar/min per ATA;
15L/bar tank (Steel HP119): 0.73bar/min per ATA;
16L/bar tank (Steel HP130): 0.68bar/min per ATA;
11L Twins (Double AL80's): 0.5bar/min per ATA;
12L Twins (Double HP100's): 0.45bar/min per ATA;
16L Twins (Double HP130's): 0.3bar/min per ATA.
The point is that SAC rate for most nominal activity on single tank is going to fall in between 1 bar/min per ATA and 2 bar/min per ATA. And how easy is it to figure factors of numbers like 1 and 2? --All you need now is a convenient time interval like 10 minutes and your metric depth converted to ATA as multiplying factors, and you will then know what your Depth Consumption in bar will be over that time interval, with a particular tank, and level of physical activity. . .
You can get SPG's that read in both, however in North America in general it's easier to work in PSI and cubic feet for most people as those are the units our tanks are sold.
I have bar spg's on some of my regulators, but PSI is easier for most people to work with so I usually end up having to convert back
So to recap, it's actually
a lot easier working with multiplying factors of 1 bar/min to 2 bar/min SAC rates in Metric, versus handling factors of 14.5 to 29 psi/min in US Imperial units.