US divers using metric?

[KenGordon]

But a newton is a measurement of energy or force is it not?

Of force. Force * distance = energy. Thus newtons * metres = joules.

Here we had "metric martyrs". These were the people that insisted on pricing goods in £/lb rather than £/kg or indeed the reasonable and comparable solution of showing both. Since the UK press is generally anti European and not run by mathematicians or physicists these people where held up as heroes.

Here children have been taught the metric system since I was at school, but we use miles to discuss the distance to a marina and meters to discuss depth.

Can anyone work out the mass of gas in a 3000 psi Ali 80 using imperial units without reference to anything more than a periodic table? No cheating and using scales

On the other hand...

Many people have decided they cannot do mental arithmetic at all, let alone at 20m. Thus whether the numbers are easy or not will not help. I would hope that easier numbers would make for fewer of these people but here at least that doesn't seem to be the case.

Ken

 

[dmoore19]

In the 60's, when I was in school, we were taught some conversions and told we would be going metric. So far it hasn't happened. I get all of it and with some effort and practice it would become easier. It's just a matter of knowing what the numbers are. Like before 2.9 bar for tire pressure just doesn't register and I have to think about it.

The first time I saw pressure in kPa I almost freaked out. 3000 PSI is +/-20,700 kPa, not exactly what I was expecting when I saw it. Same thing with cubic feet and cubic meters, it still messes with me but I can figure it out of I have to. The numbers just don't make sense.

 

[dfx]

In the 60's, when I was in school, we were taught some conversions and told we would be going metric. So far it hasn't happened. I get all of it and with some effort and practice it would become easier. It's just a matter of knowing what the numbers are. Like before 2.9 bar for tire pressure just doesn't register and I have to think about it.

The first time I saw pressure in kPa I almost freaked out. 3000 PSI is +/-20,700 kPa, not exactly what I was expecting when I saw it. Same thing with cubic feet and cubic meters, it still messes with me but I can figure it out of I have to. The numbers just don't make sense.

It's all a matter of getting used to it. I have no problem with diving in imperial because depth in meters and water temperature in °C and pressure in bar don't make any more sense to me than feet, °F and PSI. For my type of diving, it makes no difference at all.

I have to admit that the two "competing" pressure units are one of my pet peeves of the metric system, but it's not a very big problem. 1 bar = 100,000 Pa = 100 kPa = 1,000 hPa. Thus incidentally, 1 hPa = 1 millibar. All those are precise values and if you keep those in mind, you're good. 20,700 kPa = 207 bar.

The nice thing about the SI system is that there's a very small number of base units and all other units are derived units. Kilogram, meter and second are base units, newton is not and neither is bar nor pascal. That's why it's such a coherent system and the numbers and multipliers all come out so nicely. In imperial, you can measure volume as either cubic feet or cubic inches (where 1 cu ft = 1728 cu in), or you can measure in the completely unrelated fluid ounces or even gallons, which are also measures for volume, where 1 cu ft = 7.48052 gallons and 1 cu in = 0.554113 fl oz. It just doesn't make any sense.

 

[Kevrumbo]

I have wondered why GUE never standardized imperial or metric. Everything else is standardized; why not this?

It's likely to allow regional preferences......but I can only guess.

Personally, I dive metric. I didn't find it that difficult to switch.

I think it's an easier system to use, except for temperature.

-Mitch

Practical temperature conversions deg C to deg F for typical human habitable ranges: just double the deg C value and add 30 to get the deg F conversion. For a little better accuracy use these "fudge" subtractions for these temperature ranges:

minus 2: for conversions totaling in the 70's;
minus 4: for conversions totaling in the 80's;
minus 4: for conversions totaling in the 90"s;
minus 6: for conversions totaling in the 100's

Examples:
25 deg C, double it yields 50 and add 30 makes 80, and minus 4 equals 76 deg F.
37 deg C, double it yields 74 and add 30 makes 104, and minus 6 equals 98 deg F.
15 deg C, double it yields 30 and add 30 equals 60 deg F (no fudge subtraction needed).

 

[ajduplessis]

What! No Truk invoice to give this substance

 

[Kevrumbo]

C'mon y'all . . .is this thread turning into my own personal Blog on how to OBJECTIVELY/PRACTICALLY utilize the Metric System for Scuba both here in the US and abroad???

Sad to say, but the irony is most American hard core "GUE Practitioner Divers" are totally ignorant even when you try to explain the advantages of metric units in gas planning versus US Imperial units (I bet founder Jarrod Jablonski and even old timer "Red Neck" GUE Instructor David Rhea use a bar SPG on their fun & mission oriented dives!).

And yet some more examples & explanations on the advantages:

Discovered an interesting one-to-one correspondence between depth and gas consumption rate in bar/min, while diving with double AL80's (and why I now prefer using the Metric System even here in the States). An example:

18m depth, same as 2.8 ATA -->translates directly to 2.8 bar/min
21m depth, same as 3.1 ATA -->translates directly to 3.1 bar/min
24m depth, same as 3.4 ATA -->translates directly to 3.4 bar/min
27m depth, same as 3.7 ATA -->translates directly to 3.7 bar/min
30m depth, same as 4.0 ATA -->translates directly to 4.0 bar/min

So for an arbitrary & convenient time period of say, for example 10 minutes, at a particular depth above, you would expect to consume:

2.8 bar/min(10min) = 28 bar
3.1 bar/min(10min) = 31 bar
3.4 bar/min(10min) = 34 bar
3.7 bar/min(10min) = 37 bar
4.0 bar/min(10min) = 40 bar

Essentially then, all you need to know is your depth in ATA and your time at that depth, and you'll know instantly how much gas you've consumed --even before looking at your SPG!

Parameters:
Surface Consumption Rate (SCR): 22 litres/min*ATA
Twin 11 litre tanks (double AL80's): 22 litres/bar total tank rating.

Now divide SCR by total tank rating (22 divided by 22). You get: 1 bar/min*ATA (and there's the secret math trick discovered --the unity conversion ratio of 1 bar/min*ATA which lets you transform directly from depth to a delta bar per minute rate, and subsequent SPG bar consumed).

So ideally, the motivation is to electively use a tank cylinder (or twinset doubles cylinders) to match your own volume Surface Consumption Rate for a convenient 1 bar/min pressure Surface Consumption Rate. For example, if you have a 15 litre/min volume SCR (same as 0.50 cubic ft/min US Imperial units), get a 15 litre/bar rated cylinder --a Steel LP95 or HP119 Tank-- to give you a 1 bar/min SCR. Of course your consumption at depth, (DCR or Depth Consumption Rate) depends on your ATA depth as a multiplier factor (Atmospheres Absolute ATA multiplier factor is simply your depth in meters divided-by-ten and add one: So 30 meters equals 4 ATA; 28 meters equals 3.8 ATA; and so on). . . Therefore your DCR at 30 meters depth will be 1 bar/min multiplied by 4 ATA equals 4 bar/min, and you know after 10 minutes of nominal breathing that 40 bar of gas will be consumed (4 bar/min multiplied by 10 minutes equals 40 bar).

Don't any of y'all US Divers see the elegant power & ease of smartly calculating in your head, vital gas usage -both pre-dive & real-time on-the-fly- all by using the Metric System?

What! No Truk invoice to give this substance

Sure thang sugah. --I'll travel 9800km to dive in 28 deg C tropical waters-- and send ya the bill !

 

[rivers]

I haven't read the entire thread, but as an american living in the UK and using a mix of metric and imperial, a few easy conversions.

3 metres is approximately 10 ft.
750 psi is approximately 50 bar. 1500 psi is about 100 bar and 3000 is about 200 bar. most people can remember that.
Good luck with temperature. That is not an easy conversion. Low single digits=f*cking cold, high single-low teens= cold to not really cold but not warm, mid teens= warm, high teens to low 20s: positively tropical. We don't really see higher than 22* though

Use what you're comfortable with. I learned both metric and imperial systems growing up, so when I moved to the UK, I just switched my vyper from imperial units to metric. It wasn't a big deal and it me on the same page as everyone else during a dive. My spg, however, is still psi. I see no reason to change it a) still works and B) I can communicate how much gas I have left in bar to whomever I'm diving with. Although, an instructor I know keeps threatening to buy me one in bar (the spg on my stage is in bar however)

 

[PfcAJ]

Makes me wonder how any of us ignorant American DIR guys make it out alive without using metric.

One thing's for sure, I never see Kev doing anything other than a)ranting on SB about metric or b) telling everyone about his 'hero' dives in Truk.

 

[Nemrod]

We do not care nothing about no stinking metric!

N

 

[DuboisP]

My spg, however, is still psi. I see no reason to change it a) still works and B) I can communicate how much gas I have left in bar to whomever I'm diving with. Although, an instructor I know keeps threatening to buy me one in bar (the spg on my stage is in bar however)

even US instructor can understand a SPG in bar, i tried it.
"do you have a red zone ?"
"i have"
"so, that's OK for me"