Metric or Imperial?

[BoltSnap]

You regard the use of a watch, a depth gauge and an SPG while submerged during a dive as a math application? Using the tables is basic and simple, more application, not really calculation.

Serious calculation belongs in pre-dive planning. Most contingencies should be covered by substantial safety margins and common sense.

Agree, and writing contingency plans that were worked out on the surface on a slate as to prevent/reducing the chance needing to do calculations at depth especially when under narcosis and one doesn't have the luxury of time to do the math and double/triple his calculations as he would have on the surface.

 

[Patoux01]

in the US, you are told the total capacity of the Tank (how much volume of gas it will hold), i.e. 130ft3, 100ft3, 40ft3, etc.

It's just too bad that an al80 doesn't hold 80cuft... (and so it goes for a few others as well, like the + tanks that lose 10% of capacity, as they're given with "total capacity at 110% of service pressure")

 

[BoltSnap]

It's just too bad that an al80 doesn't hold 80cuft... (and so it goes for a few others as well, like the + tanks that lose 10% of capacity, as they're given with "total capacity at 110% of service pressure")

Why would they lose their + capacity??? If you go to a hydro test facility that actually knows the standards and knows what they are doing, they would put the + (if appropriate). The steel tanks made in Europe don't have the + sign BTW, what it says on the tank is what it is and one doesn't worry about the +.

The Al80 made by Luxfer actually holds 77.4 ft3 when filled to its service pressure, hardly anything to complain about here with less than 3ft3 discrepancy. If you want to be precise about it and don't want to round up, you can still say 77.4ft3 and you will still get information about the actual capacity of the tank from one piece of information without having to get another piece of information yet to multiply it to get the final piece of information

XS Scuba Luxfer Aluminum Scuba Cylinder Specifications

No "+" here:

http://www.xsscuba.com/downloads/Faber-Steel-Specs.pdf

 

[Kevrumbo]

You regard the use of a watch, a depth gauge and an SPG while submerged during a dive as a math application? Using the tables is basic and simple, more application, not really calculation.

Serious calculation belongs in pre-dive planning. Most contingencies should be covered by substantial safety margins and common sense.

Basic Instruments as taught in beginning open water: 1) a watch indicates elapsed Time (minutes); 2) a Depth Gauge (meters or feet); and 3) SPG (pressure in bar or psi).

Knowing your own consumption rate, you claim there is no motivation to mathematically derive & apply the instrument readings of 1 and 2 above to be confirmed quantitatively at depth by 3 . . . ???

So in any case then, again explain objectively your opinion how "it has nothing to do" with math application of a depth gauge, timer and SPG: Basic Tools in either metric or imperial that we were all fundamentally taught to use from basic open water course, and learn how to use smartly as we progressed with experience and advanced courses.

Better yet, show some "serious calculations" for your Pre-Dive Plan. . .

 

[Kevrumbo]

Agree, and writing contingency plans that were worked out on the surface on a slate as to prevent/reducing the chance needing to do calculations at depth especially when under narcosis and one doesn't have the luxury of time to do the math and double/triple his calculations as he would have on the surface.

Yes, it's good practice when first learning Gas Management to write the evaluations on a slate or wetnotes. But after experience and rote practice & learning the same profiles over and over many logged dives, these "serious calculations" can be applied smartly and expeditiously, even at depth. (As an Instructor, you should know this . . .don't you?)

The point is that it's easier and takes less cognitive "bandwidth" to do the math both pre-dive and realtime on-the-fly using the Metric System: Again what's so hard arithmetically working with quantities like 1 or 2 (bar per minute) to start with, or any real number in between?

 

[agilis]

Basic Instruments as taught in beginning open water: 1) a watch indicates elapsed Time (minutes); 2) a Depth Gauge (meters or feet); and 3) SPG (pressure in bar or psi).

Knowing your own consumption rate, you claim there is no motivation to mathematically derive & apply the instrument readings of 1 and 2 above to be confirmed quantitatively at depth by 3 . . . ???

So in any case then, again explain objectively your opinion how "it has nothing to do" with math application of a depth gauge, timer and SPG: Basic Tools in either metric or imperial that we were all fundamentally taught to use from basic open water course, and learn how to use smartly as we progressed with experience and advanced courses.

Better yet, show some "serious calculations" for your Pre-Dive Plan. . .

Know your consumption rate? My consumption rate is extremely variable, depending on level of activity, water temps, depth, all kinds of things that are only partially predictable. Perhaps your consumption rate is more predictable than mine.

I learned to dive in the early 1960s from a book, and was certified about 10 years later. SPGs were not part of my first decade of diving. We used J valves and a lot of pre-dive planning, especially when diving the deep cold offshore wrecks.

Truthfully, I can't relate to what passes for dive training in this millennium; I'm unfamiliar with too many of the concepts. When I found out that doff and don drills were no longer part of basic pre-certification requirements I was horrified and lost interest.. Too many things have changed, and too many divers are not completely comfortable in the water.

I'm quite old now, but when doing recreational dives in the tropics I've noticed that the DM and I tend to return with more gas than most of the other divers. A hell of a lot more. I'm not sure what this signifies, but I do watch my SPG as compulsively and frequently as I once checked the position of my J valve actuator rod, only to find myself hanging on the ascent rope with enough gas for another dive while the DM is offering sips of air from his octo to divers with worried looks and bulging eyes.

This seems to be true of those using metric (the majority in the islands I favor) as well as imperial.

 

[BoltSnap]

Yes, it's good practice when first learning Gas Management to write the evaluations on a slate or wetnotes. But after experience and rote practice & learning the same profiles over and over many logged dives, these "serious calculations" can be applied smartly and expeditiously, even at depth. (As an Instructor, you should know this . . .don't you?)

The point is that it's easier and takes less cognitive "bandwidth" to do the math both pre-dive and realtime on-the-fly using the Metric System: Again what's so hard arithmetically working with quantities like 1 or 2 (bar per minute) to start with, or any real number in between?

I am not sure what we are arguing about here or if we are on the same channel. At the end, it is really up to where you are and what your dive buddies are using. You are controlled to a great extent by local culture and standards.

In regards to learning by "rote," I am not sure that I'd agree here. We are talking about recreational diving within recreational diving limits here. One needs to plan their dives on the surface and accounting for emergencies during the dive plan on the surface not U/W. If I have an "emergency" U/W, I'd go up and not wait at depth (in most circumstances). I'd activate my contingency plans I prepared on the surface.

BTW, it is very difficult to understand what you are getting at here to justify having to do "back of the envelope" calculations underwater. Perhaps you can provide a real life experience you have had so that we can have a more focused discussion.

BTW, when doing the same profile and with lots of experience, I can "guesstimate" how long my air is going to last me at a certain depth at a certain effort without having to do any calculations. It is a guesstimate based on decades of experience and thousands of dives where one develops "feeling" for their limits and performance U/W. For "ME," the imperial system gauges/units provide me with better "feeling" and much higher resolution for the data I need for my equipment. It is no big deal however and the controlling factor here will be the locale and dive buddies and what they use.

 

[Lorenzoid]

From looking at the different dive computers, at least the ones I'm reading about calculate in both. My big issue is I am not too good with math, but doing calculations in metric I feel a lot less dumb. lol

I was referring to gas calculations, not the computer's calculations. You mentioned wanting to do tech diving. In tech diving, you're doing calculations involving gas consumption. You might, for instance, have to figure out what "turn pressure" each of you needs to see on your gauge to indicate that two thirds remain of the original gas volume in whoever's tank held the least volume at the start of the dive. And each of you needs to agree that the other's calculation of his turn pressure is correct. If one of you has a gauge in bar and did his calculation in bar, while the other has a gauge in psi and did his calculation in psi, well, you can see the complication and unnecessary increase in the likelihood someone is going to make an error.

 

[JohnnyC]

Ok, you got me. An LP72 has 72cuft of gas in it at 3psi. Right? Because sure the pressure of the vessel doesn't make any difference.

And your imperial spg faceplate, that's moving the same degree of swing as my metric faceplate spg is totally more accurate. Right? I mean, I guess I could paint individual bar marks on my SPG's and have higher resolution, after all, despite the fact they move the same distance and display the same volume of gas, it's all about what you think is correct right?

Not to mention metric depth gauges display in tenths of meters, which is higher resolution than your imperial depth gauge if you want to make the argument that resolution of display convention makes any amount of difference.

Seriously dude, you're wrong. Pressure is absolutely a part of determining usable gas volume in both metric and imperial. Only in imperial you have an even more complex calculation. And spg's, 100% identical except for the screen printing on the faceplate, with the exact same amount of swing showing exactly the same amount of volume, moves exactly the same distance for volume consumed. Now, that's not even taking into consideration the error inherent in mechanical spg's, nor is it remarking on the fact that if you're planning gas down to the psi you're and idiot who shouldn't be diving because you've decided red c*nt hair margins for safety are ok.

 

[Storker]

6.6% which is [...] Still not insignificant

I've got an AI computer, so my gas consumption is logged for every dive I do. My SAC/RMV/whatever you call it varies from 14 SLM to 20 SLM, my normal range is 15-18 SLM. That's some 20% difference. Compared to that, a 6% difference due to nonideality isn't particularly significant. The ~10% difference between a 200 bar and a 300 bar tank that I quoted is marginally significant.