Metric measurements?

[Bob DBF]

Submarine pressure is easy in metric but not really really hard in Imperial.

The pressure in a submarine is kept at about one atmosphere. The highest I've seen is two atmospheres for a leak test, and the lowest at nearly 8000' on the altimeter in engineering.



The ease in using metric or imperial is dependant upon how much you use the system. So it isn't so much that you get it, it is whether you use it. Living where imperial is the convention, there is no reason for me to use metric, say for gas planning, especially when all my dive buddies would be using imperial. It would be the same issue if the OP started using imperial with his buddies.

When in Rome...


Bob

 

[Manatee Diver]

I understand you were just giving one example (got another?), but as far as that example is concerned, if I significantly overfill my "LP" whatever tank beyond its rated working pressure, which is not uncommon, then I still have to go through the calculation to know how much gas I have.

True, but cave fills are the exception rather than the norm.

I get the impression that nowadays, with HP tanks being so common and HP fills being more widely available, only people who routinely overfill their LP tanks still prefer them over HP.

LP tanks are great if you can find a local shop that can give you cave fills, but I have a hard enough time getting a decent HP fill locally let alone convincing the fill dude that a cave fill is perfectly fine. So my LP tanks mostly gather dust.

 

[Manatee Diver]

Yes but calculating consumption is easier

For a 12l tank, 1 bar=12l on a 15l tank, 1 bar=15l, So if you know you're breathing 15l/m at the surface you can easily figure that to be 4bar/m at 30min

It isn't hard to do the math using cuft/min either.

I am versed in both systems, I think they both work, but what you are used to is more important. Because when you are adrenaline spiked, or narced you need to use something that you can work with without thinking.

 

[TGIF]

I switch between imperial and metric all day. The bit that drives me nuts is the difference between metric and imperial tons and and the different gallons.

 

[broncobowsher]

Ever go shopping for car tires? Tire width is metric, rim diameter is imperial inches.

Those 80's Michelin TRX metric tires never caught on.

 

[Searcaigh]

Having a scientific background metric is totally ingrained in my brain, but also hailing from part of the UK I totally understand Miles per Gallon even though fuel is measured in litres now.

When I was sitting exams as a chamber operator back in the 80s I converted all imperial measurements to metric then converted them back to imperial (showing my working of course).

When learning to fly I was never bothered that altitude was measured in feet rather than metres, it somehow made more sense to me, I don't know why.

 

[Lorenzoid]

True, but cave fills are the exception rather than the norm.



LP tanks are great if you can find a local shop that can give you cave fills, but I have a hard enough time getting a decent HP fill locally let alone convincing the fill dude that a cave fill is perfectly fine. So my LP tanks mostly gather dust.

Right--that's exactly what I meant. These days, it's pretty much only people in "cave country" who prefer LP tanks. So, like yours, LP tanks are mostly gathering dust. Hence, there is little utility nowadays in being able to readily determine that an "HP 100" contains roughly as much gas as an "LP 100" by virtue of the tank capacity being stated in cubic feet at working pressure.

 

[loosenit2]

I wonder how many Scubaboard users are familiar with metric measurements (m, kg, litres, °C, bar, etc)? Obviously, everyone outside of the US now uses metric but how many American divers get it?

I am familiar with metric and can use the metric system, but we don’t necessarily “think” in metric. Big difference between being able to speak another language and truly think in another language.

 

[Bob DBF]

For a 12l tank, 1 bar=12l on a 15l tank, 1 bar=15l, So if you know you're breathing 15l/m at the surface you can easily figure that to be 4bar/m at 30min

For a 80cuft tank, 1 bar=80cuft on a 100cuft tank, 1 bar=100cuft, So if you know you're breathing 1cuft at the surface you can easily figure that to be 4atm/m at 30min


Before you start with an Al 80 is only 77.4, read Calculating SCUBA Cylinder Capacity | Dive Gear Express®

From the article:
" A 10 L cylinder at 232 bar does not contain 2320 free liters of air! Divers using metric cylinders are fond of saying they don't have to deal with this stuff, just multiply the water volume in liters by the working pressure in bar, but that's not entirely correct. Many divers think that atmospheric pressure is defined as 1 bar. A bar is actually defined as exactly 10 meters of sea water, not 1 atmosphere. The metric calculation typically used by divers omits the division by atmospheric pressure, which is 1.01325 bar. That makes the ideal capacity overstated by 1.3% plus the difference between ideal and true capacity for a total variance of ≈8% at 232 bar and ≈11% at 300 bar. Notice the "Ali 80" actually has a larger true capacity compared to the "10 Litre" with a larger ideal capacity; that's the effect of compressibility between the two different working pressures."

So 'close enough for government work' is the operative phrase whether you use metric or imperial.


Bob

 

[ScubaWithTurk]

I am American and never used metric except as a machinist. I know the conversion factors by heart.

During my OWC I hated the questions where I needed to figure out how many ATMs is 57'.

Then I came to the UAE and was told I would need to use metric. well damn!! Then I saw how easy it was. 10 meters = 2 atms, 3 =4 and so on. Pretty simple. Liters of gas is much easier to work out than doing PSI IMO. The math is easy and has less steps.

I still can't think in metric. I can't visualize 39 cm. I know I am certified to 50 meters but I need to convert to wrap my head around it. Although I usually don't care as my computer, deco software, etc is all set to metric.

IMO, metric in diving is MUCH more user friendly and that is my 2 bar.