Metric versus Imperial System for Diving?

[dmoore19]

What is the problem? It only takes a rudimentary understanding of basic math to convert from one to the other and back again. It isn't scientific so I guess it must not be worth knowing? BTW that is a pretty strange sized wrench in metric or imperial.

 

[dfx]

1 13/64 (I think), or a tiny hair over 1 3/16. This took about 10 seconds done in my head, and I just swallowed an ativan after a hot bath. Bad tinnitus day. one of those souvenirs I wish I could have left in country.

Good for you, and that's about 10 seconds wasted in my book. I haven't checked BTW and I haven't got a clue myself, because outside of algebra, I have no use for dealing with fractions.

 

[RJP]

Good for you, and that's about 10 seconds wasted in my book...

He says... in Post #193 of this thread.

How do you measure irony in metric units?

:d

 

[BRT]

Good for you, and that's about 10 seconds wasted in my book. I haven't checked BTW and I haven't got a clue myself, because outside of algebra, I have no use for dealing with fractions.

DFX, maybe you could add up 14.684375 mm plus 15.875 mm in your head real fast.

 

[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"?

 

[Storker]

14.684375 mm plus 15.875 mm

You've got a measuring device with nanometer precision? I want one of those.

Jeez, some of you guys just don't get it, do you? When you say 4 inches, we don't say 10.16 cm. We say 10 cm. When you say two feet, we don't say 60.96cm. We say 60cm or a little more than half a meter, depending on what kind of precision we need. When you say a mile, we don't say 1.609km, we say about a kilometer and a half. We don't care if 1 bar isn't exactly 1 atm isn't exactly the pressure increase for every 10m we descend. It's precise enough. And when you eyeball something to about 6ft, we eyeball it to about 2m.

Arguing about conversions from US to metric with a precision of eight significant figures is just silly. Or stupid.


BTW, just to put some perspective on the sillyness of using fractions of millimeters to eight significant figures: one nanometer, or 0.000001mm, is roughly ten times the size of an atom.


--
Sent from my Android phone
Typos are a feature, not a bug

 

[dfx]

BTW, just to put some perspective on the sillyness of using fractions of millimeters to eight significant figures: one nanometer, or 0.000001mm, is roughly ten times the size of an atom.

I propose we rename nanotechnology to 1/33,554,432 inch technology.

 

[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. . .

 

[RJP]

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?

 

[DaleC]

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.