Metric versus Imperial System for Diving?

[victorzamora]

First of all, tank factor is water volume....kinda. It's the same number and math as in metric.

Secondly, you must SUCK at math. 2800/2640*95 is the volume in cubic feet. It's just a ratio. Underwater, it's WAY more than close enough. Quicker than you can do your mental math, I can mentally tell you you're rockin 100ft3 in them there tanks.

Thirdly, you must suck at diving and dive planning. Under no circumstances have I needed to calculate remaining air volume in the water. Planning and math are at the surface. When do you ever need to recalculate the exact number of "cubic liters" you have in your tank? Ignore the fact that cubic liters requires 9 spatial dimensions.

Fourthly, calling tanks by the air they can hold at rated pressure is great because I don't have to do secondary math when I'm doing gas planning. "I need 240ft3 of gas with reserves for this dive. Let me take two 120s." I like the metric system as well, but you can't say there are no advantages.

I feel like this post had multiple good points and they were all ignored over the "cubic liters" comment. So, I'll summarize them as questions and ask the Metric crowd to chime in. Please note, I agree that diving in metric is easier and have been very tempted to pull that particular trigger (it would just require different names for tanks and different SPGs, plus a few buttons on my computers).

1) What's wrong with tank factor? You don't dive 100 different tanks, most people only dive a few different sized tanks. By that token, memorizing a few numbers is no different than memorizing tank sizes the way the metric guys do. Then it's just multiply by pressure and you've got ft3 remaining. I only dive with like 3 different sized tanks, and if I were incapable of further math I'd simply remember the tank factors (which are: 2.7, 2.8, and 3.9).

2) Have the metric guys considered how easy the "ratio method" (my term for my method) is for calculating remaining gas? It's current pressure over rated pressure times rated volume. This is the same math as with tank factors, but easier as there's no memorizing tank factors. Not as easy as pressure*volume on paper, but my math is quicker than the math shown earlier.

3) What dive planning occurs underwater that requires quickly calculating remaining tank volume that tank pressures couldn't suffice. The example earlier was lost buddy search, which I posited tank pressures were MORE than sufficient and much easier (metric or impreial). I simply can't imagine a scenario where that's such a huge benefit, honestly.

4) What about the fact that I don't need to do anything but know total breathing gas needed and pick tanks that add up to it? If this dive requires 240ft3 of gas, my double 120s would be great. 300? My cave-filled 104s would be great. 350? I'm adding an AL80 to my 104s and carrying a smidgeon extra. In liters, if you need 10,000L (cubic or regular liters, your choice )....what tanks would you carry with you? 2*12L*230bar=5520L, but 2*15L*230bar=6900L, or 2*15L*300bar=9000L. This is an honest question. It's a piece of CAKE in imperial, but a pain in metric...to me. I'm unfamiliar with metric tank sizing, though so please tell me how you'd do it.

PS- Remember, I'm not saying metric doesn't make some things easier. My statement is that if I'm thinking in imperial and have to convert all of my numbers over mentally before using them it's more work. My diving in imperial is fine and I've yet to have a problem with it.

The first time I encountered Bar in diving (after diving all over the Caribbean, Roatan, Belize, Mx, etc) was my most recent trip to Playa. A Spaniard guide there was diving Bar and two guests were German diving Bar (and yoke, which I thought was hilarious). He asked what we'd rather do because we were mixing units. I told him we (wife and I) would just tell him when we were low at a preset limit. Deeper dives means higher pressures. I'd signal "low" and we'd surface. When he asked pressures, I told him I'd give it to him in Bar. My wife and I divided our PSI by 15 and called it close enough (14.5psi/bar). At 2100PSI I was at 140bar. I'd just tell him 140 (signalling "1-4"). He said we should just give it to him in PSI, but we told him Bar was fine and it'd keep all numbers consistent. We only used PSI with eachother and with the non-bar guides. Of course, we rarely gave actual pressure values to eachother....it was typically "half tank" and "low air" signals.

 

[Diver0001]

Storker... easy.

Like I pointed out above, someone can learn to find imperial "natural" and metric "foreign". I would say that you may be that way too but in reverse.

For people whose thinking or performance is not inhibited by that, there is no problem. You and victor are trying to convince each other that your own way of thinking is "easier". Forget it. Like I did with my father (see above post) you both have to accept and believe that for the other it must be easier.

.... and for the time being at least (our generation and the next) there won't be a change because the costs involved in standardizing world-wide on the metric system is too high.

so we just have to accept that the two systems aren't going to disappear any time soon. Maybe they will as some point, but you, me and victor will all be reduced to ash and bone well before that end game is played. It's not a job for our time line. OUR job is to accept the status-quo and find a mode to translate because that's all we have. Maybe at some point in the future it will make sense to take a stance but in our current time line we're not going to win any ground by pointing at a point on the horizon that we can't reach without intermediate steps.

My father's wisdom fits nicely here.... 100 more years, all new people. This is the time scale we need to be looking at.

R..

 

[victorzamora]

you can round up 14.8 to 15 or 14. if you round up to 15 you get 190 * 10 + 190 * 5 = 1900 + 190/2 * 10 = 1900 + 950 = 2850 cubic liters. 2800 is a good estimate (assuming we chose 15 instead of 14.8).

Just for future's sake, I wanted to clarify WHO posted cubic liters.

 

[Storker]

I pity those unfortunates who are deprived of the joys of fractional calculations. The appeal is almost erotic in its intensity.

I'm not the one to judge people by their preferences, whether here or there. Consenting adults and all that. Live and let live is what I live by.

That said, complex fractions isn't my... preferred... math. Having been brought up with the metric system, I much prefer decimals.

---------- Post added October 28th, 2014 at 08:45 PM ----------

Like I pointed out above, someone can learn to find imperial "natural" and metric "foreign". I would say that you may be that way too but in reverse.

Replace "foreign" by "obsolete", and we can agree perfectly

 

[mrdre]

Just for future's sake, I wanted to clarify WHO posted cubic liters.

On my part it was obvious mistype, nobody ever would think about 9 dimensional measurement. Nobody even paid attention. But you started with outright attacks that I suck in everything I do begging for me to simply ignore you and all your "good points". That's just for "future's sake". Maybe one day you learn how to argue in a civilized manner and you may deserve my reply.

 

[agilis]

I'm not the one to judge people by their preferences, whether here or there. Consenting adults and all that. Live and let live is what I live by.

That said, complex fractions isn't my... preferred... math. Having been brought up with the metric system, I much prefer decimals.

Perhaps the use of metaphors does not translate well into metric thinking.

Decimals and fractions are simply different notational symbols for exactly the same things: segments of a unit. They are equally convenient and equally easy to calculate, unless the capacity for envisioning abstract numerical relationships has become atrophied from disuse. I tend to do both simultaneously. They are nothing more than two perspectives, two vantage points for observing the same object; to employ another metaphor, the facilitation of three dimensional perception.

 

[JohnN]

On my part it was obvious mistype, nobody ever would think about 9 dimensional measurement. Nobody even paid attention. But you started with outright attacks that I suck in everything I do begging for me to simply ignore you and all your "good points". That's just for "future's sake". Maybe one day you learn how to argue in a civilized manner and you may deserve my reply.

Damn, I wish the rest of us were that lucky. . .

 

[dfx]

1) What's wrong with tank factor? You don't dive 100 different tanks, most people only dive a few different sized tanks. By that token, memorizing a few numbers is no different than memorizing tank sizes the way the metric guys do. Then it's just multiply by pressure and you've got ft3 remaining. I only dive with like 3 different sized tanks, and if I were incapable of further math I'd simply remember the tank factors (which are: 2.7, 2.8, and 3.9).

Because it's a pointless exercise, that's why. The imperial system is full of pointless exercises, none of which are required in metric, because it's simply better designed (I would even argue that the imperial system isn't "designed" at all, which is the main problem). You don't have to "remember" tank sizes in metric, because the internal volume is what determines the type of tank. There's 12L tanks, 15L tanks, etc. It's just what they are. But in imperial, you don't dive "factor 2.9" tanks, you dive 95 ft³ tanks. This factor business is nothing but a crutch.

4) What about the fact that I don't need to do anything but know total breathing gas needed and pick tanks that add up to it? If this dive requires 240ft3 of gas, my double 120s would be great. 300? My cave-filled 104s would be great. 350? I'm adding an AL80 to my 104s and carrying a smidgeon extra. In liters, if you need 10,000L (cubic or regular liters, your choice )....what tanks would you carry with you? 2*12L*230bar=5520L, but 2*15L*230bar=6900L, or 2*15L*300bar=9000L. This is an honest question. It's a piece of CAKE in imperial, but a pain in metric...to me. I'm unfamiliar with metric tank sizing, though so please tell me how you'd do it.

You're doing it backwards. If you need 10,000L of breathing gas (sounds like a lot to me), divide by your fill pressure and you know how much tank volume you need. 10,000/200 = 50L. You'd need 2x 25L tanks (I don't think they make them that big lol), or 5x 10L tanks, or w/e. Or if you can do 300 bar fills, 10,000/300 = 33L. 3x 12L would fit nicely. Or you can divide your 10,000L by the combined volume of all the tanks that you have and figure out how high of a pressure you'd need. Let's say you have 2x 15L tanks, 10,000/30 = 333 bar.

BTW this isn't really a feature of either system, it's just a convention. You could label tanks by how much gas they hold in metric too (you'd have 3,000L tanks) or you could label tanks by internal volume in imperial (e.g. a 3 3/4 gallon tank ). It's just that they don't. I recognize the convenience the imperial convention provides, but I still prefer the metric convention because it doesn't depend on the fill pressure. A 95 ft³ tank only holds 95 ft³ of gas if it's filled to a particular pressure, while a 12L tank is always 12L no matter what.

PS- Remember, I'm not saying metric doesn't make some things easier. My statement is that if I'm thinking in imperial and have to convert all of my numbers over mentally before using them it's more work. My diving in imperial is fine and I've yet to have a problem with it.

And I could dive in Burmese units and also not have a problem with it. And I would also come up with all kinds of crutches to solve the little problems that such a system provides, and I'd be fine using those crutches and remembering all the little magic numbers that I need, because that's just what I know and that's what I've been doing all the time. But there's a better system where you don't need any crutches! And even better, everybody else is using it too. What should I do, embrace it and try to make the change to benefit in the long run, or be like "oh this works for me, so no thanks?"

---------- Post added October 28th, 2014 at 04:04 PM ----------

I pity those unfortunates who are deprived of the joys of fractional calculations. The appeal is almost erotic in its intensity.

Fractions are awesome. My favourite one is -1/12. Exponentials are awesome too, and so are imaginary and complex numbers. And roots. Not the ones you trip over though. Did I mention logarithms?

I use none of these in everyday life.

 

[Tigerman]

....
A 95 ft³ tank only holds 95 ft³ of gas if it's filled to a particular pressure, while a 12L tank is always 12L no matter what.
...

not only that, but an al80 dont even hold 80 cuft when filled to its rated pressure, just to make it extra confusing...

 

[mrdre]

Besides this thread (these conversations happen all the time everywhere) the line of reasoning usually goes like that: "I'm not saying metric system bad, it definitely has some advantages, I use both systems, I can use both systems if I want to, but I don't want to, I don't need it, it sucks, Europeans suck - traitors, Canadians suck - traitors, I don't need to do any math, I don't need that accuracy, I'm fine where I am, I have rights, I can do whatever I want, don't tell me what to do."