Metric versus Imperial System for Diving?

[DaleC]

Dude!
I'm standing right here...

 

[agilis]

I sumtimes (math pun) use a bar spg and find it to be.. well.. pretty darn interesting.

It has a little orange pie piece in there (probly pumpkin) that I think means "time to head home", so I just swim along till I see the needle bouncing around in there somewhere. Technically, they call it the "fifty bar mark" but I prefer the term "fiddy bar marky mark" because it makes me think of attempting to do a beat box improv which passes the time while hanging out in the shallows.

This is precisely how bar spgs are meant to be used.

 

[Tigerman]

Isn't it the "50 cent" mark though?

 

[agilis]

a(n) SPG in bar units used with a set of double LP95's will also indicate remaining volume in cubic feet, to a reasonable approximation. . . So the answer is true!

Utterly useless information. I don't dive in order to make calculations.

 

[Kevrumbo]

Let's do some gas planning practice starting with a 0.75 cuft/min SAC rate (also known as RMV -Respiratory Minute Volume, or also referred to as Surface Consumption Rate "SCR", a term I like better), a common rate that most novice divers can achieve. 0.75 cuft/min in Imperial is approximately 22 litres/min in Metric.


With a 22 litres/min volume SCR and a variety of different tank sizes, your pressure SCR in bar/min obviously varies inversely, depending on the size tank in use :


For the most common tank used at Dive-Ops overseas & worldwide (AL80):
22 litres per minute -divided-by- 11L/bar tank (AL80's metric tank rating): 2 bar/min;


22 litres per minute -divided-by- 13L/bar tank (an AL100 tank): 1.7 bar/min;


22 litres per minute -divided-by- 22L/bar twinset (double AL80's): 1 bar/min


22 litres per minute -divided-by- 34L/bar twinset (double Pressed Steel 104's with a cave fill): 0.7 bar/min

-----
18m Beginner/Novice OW Limit
A Quick Contingency "Rock Bottom" Calculation and Gas Plan Estimate for Open Water. . .


For a single 11 litre tank (AL80), a total of 11 litres/bar metric tank rating and a volume Surface Consumption Rate (SCR) of 22 litres/min -same as a pressure SCR of 2 bar/min*ATA (divide 22 litres/min by 11 litres/bar)- using an example NDL air dive to 30m (4 ATA) depth in Open Water.


Emergency Reserve/Rock Bottom pressure calculation, from 30 meters with slow conservative one minute ascent stops every 3 meters to the surface,


-->Just "tally the ATA's":
4.0
3.7
3.4
3.1
2.8
2.5
2.2
1.9
1.6
1.3


Sum Total: 26.5


Multiplied by 2 bar/min*ATA equals 53 bar Rock Bottom absolute reading remaining on your SPG. --this also happens to be the pressure in bar needed for one person in an emergency contingency to reach the surface with the above minimum decompression ascent profile.


So ideally for a two person buddy team, multiply 53 by 2 which is 106 bar for both to reach the surface (sharing in a buddy Out-ot-Gas contingency).


But realistically, for two experienced divers stressed: 106 bar plus 30% of 106 bar equals 138 bar Rock Bottom SPG reading.


For two novice divers stressed: 106 bar plus 100% of 106 bar equals 212 bar (!!!) --Note a full AL80 is 207 bar pressure. . .
--->obviously then, two novice divers on single 11L tanks should not be diving to 30m for any significant length of time. . .

Wait, what was the question?

Read the the main thread title --something about "Metric versus Imperial System for Diving" . . .which you and y'all playmates have contributed nuthin', Jersey Boy.

Goin' on one month now -the whole of October here in Truk & earlier in Palau. All European & Asian Dive Buddies. Ain't no feet/psi used here (even converted the Truk Stop Dive Guide originally from North Carolina to the Metric System). . .

 

[Nemrod]

I am fully fluent in Metric systems and can and have used Metric for diving. However, regardless, I prefer the US system, I prefer feet and inches, I love fractions, I like my airspeed in knots, my autos in MPH and PSI on my SPG. And I do not care if some people think Metric is easier, whatever. Maybe we need to go to a ten hour day also. I mean, those 24 hours get so confusing and then there are 60 seconds and 60 minutes and all that hard stuff. And, maybe ten months instead of twelve while we are at it. Give it a rest.

N

 

[kr2y5]

AFAIK, even GUE has not standardized on the metric system, apparently they did not think it was a big deal either way. I was born and grew up in Europe for 25 years, but I now prefer pounds, feet, and psi (you start to lose me once you begin to talk about ounces, fortunately that does not happen too often in the context of scuba diving).

 

[Hawkwood]

---

---

A ScubaBoard Staff Message...

Enough is enough. Take your off topic bickering to the Pub. If not, there will be infractions or “holidays” given to a few of you.

---

 

[Kevrumbo]

Here's a fun factoid for you US Imperialists:


An SPG gauge in bar units used in conjunction with a set of double manifolded LP95's will also show your remaining volume in cubic feet to a good approximation --same reading, same numbers, same scale and same one-to-one correspondence of bar transforming to cubic feet measurement. True or False?


Well . . .Just look at the metric tank rating for a set of double manifolded LP95's:


30 litres/bar.


And there are 28.3 litres in one cubic foot;


So 30 litres/bar divided-by 28.3 litres/cubic foot equals:


1.1 cubic foot/bar.


Therefore, a SPG in bar units used with a set of double LP95's will also indicate remaining volume in cubic feet, to a reasonable approximation. . . So the answer is true!


How's that for some "tailored numerology"?

Utterly useless information. I don't dive in order to make calculations.

Best way to fully utilize a dual unit bar & psi SPG like the OMS or ScubaPro models with a set of LP95's doubles (or the current HP119's doubles); you can actually read it to see how much pressure is remaining in either bar or psi OR refer to it as remaining gas volume in cubic feet because of the one-to-one correspondence between cubic feet and the bar units scale (i.e. Bar reading translates directly to cubic feet).

AFAIK, even GUE has not standardized on the metric system, apparently they did not think it was a big deal either way. I was born and grew up in Europe for 25 years, but I now prefer pounds, feet, and psi (you start to lose me once you begin to talk about ounces, fortunately that does not happen too often in the context of scuba diving).

If GUE ("Global Underwater Explorers") is for standardization and for best practices in diving, then they should commit to effectively teaching & using the Metric System, easier bar & meters units at least in Breathing Gas Management & Depth Calculations, which is the global standard. . .

 

[redacted]

---

---

A ScubaBoard Staff Message...

Enough is enough. Take your off topic bickering to the Pub. If not, there will be infractions or “holidays” given to a few of you.

---

My post was not ment to be off topic. It just does not matter if one system is somehow a bit better than the other. We will continue to have both systems in scuba and in other areas because a change is not economically beneficial. As long as Europeans keep providing good beer in 11.2 ounce bottles, who care?