American and english units

[ianw2]

One problem with converting America to Metric would be construction. The difficulties in building roads based on metric plans were what finally killed the "forced" conversion of all highway projects using federal dollars.

For example: a standard highway lane is 12’ wide. That’s 3.658 meters. Most plans I saw used a 3.5 meter lane. That’s half a foot less. That means vehicles are a foot closer to each other on US Federal Metric Highways! If I were an attorney working for a client who had an accident on a federal metric highway, I would be emphasizing the fact that the highway was substandard based on AASHTO standards. My defense or claim would be based on the fact that the substandard highway contributed significantly to the accident.

There simply wasn’t any thought put into how to convert everyday article in common use. Do we use a hard conversion on a 2" x 4" beam? 50.8mm x 101.6mm? Or do we use a soft conversion? 50mm x 100mm? Is the 12" ID culvert going to be 304.8mm or is it going to be 300mm? Is the minimum sight distance along a road rated at 60mph (96560.83312166624333248666497333 kilometers per hour) going to be 182.88 meters or is it going to be 180 meters? 185 meters?

Converting to metric is far more than just learning to say meters instead of feet!
BTW - I’m classically trained as a scientist, too (chemist) and now have my own private practice as a land surveyor in California (hence my knowledge of making metric plans work on the ground).

 

[Marcin2005]

ianw2, Canada did it 30 years ago and we managed not to kill ourselves in the process. BTW we still say 2x4 and a standard sheet of plywood is 12X8.

Anyhow, sorry to take this off topic. Let's talk scuba tanks

 

[Plug]

Walter,

For metric all you need to know is the water capacity and the pressure in your tank, an 11 litre tank at 200 bar has 2200 litres of air (11 x 200) if there is 150 bar in the tank the 11 x 150 = 1650l, the only difference with Leadkings method is I don't have to work out how full my cylinder is, "3000 psi 80cf tank is 2000 psi is .66 x 80= 53 cf ".
But I am sure if you are used to doing it that way it easy as well.

Now what confused me was when I lived in Canada and my gear was metric while everyone else’s was imperial.

Plug

 

[Packhorse]

With an 11 liter tank, you have to know the working pressure to know how much air is available to you.

With metric you DO NOT have to know the working pressure. Im not sure where you got that idea. You need to know the acual pressure and WC. Thats all.

I don't care how much air a tank holds when it's empty, I want to know how much it holds when it's full.

Id much rater know how much air the tank has in it at any one time. eg at the start of a dive, in the middle of a dive or at the end of a dive.

With metric its easy as WC x BAR or 10L X 150 bar
With imperial its Rated CF/ Rated pressure x actual pressure or 80 (or is it 77)/ 3000 x 1350.

And you think imperial makes more sence? Only because you are used to it. Metric is easier over all. If you knew neither and had to start using one which would you choose?

 

[Walter]

Unless one is severely brain damaged, it's easy to tell how much air a tank has at any given time in either system. I don't understand why you'd ever need to know how much a tank holds empty, yet that how the metric system defines its tanks. If I want a particular volume tank, in imperial, I can simply state the size tank I want. In metric, I must state both the tank size and the pressure. Yes, imperial makes more sense.

 

[Packhorse]

Dont think of the WC as being how much it is when the tank is empty. Think of it as the multiplyer.
WC X WP (working pressure) = Rated contents
WC X BAR = Air available
WC X Bar used = Litres used
WC X BAR resreve (eg 50bar)= Litres of reserve air.

How often does a 80 CF tank actulty have 80 CF of air in it anyway?
What more important knowing how much the tank is rated to or how much gas you actual have?
Convince me that rated contents are more important than actual contents and I will convert to imperial ASAP.

 

[grazie42]

Originally Posted by Walter
If I want a particular volume tank, in imperial, I can simply state the size tank I want. In metric, I must state both the tank size and the pressure. Yes, imperial makes more sense.

But so much more than volume of gas is involved in tank choice.
8lx300bar=12x200bar in volume, but differ significantly in lead required and bouyancy characteristics. Same for 10x300bar=15x200bar though even more so!

I´d hate to leave a choice that impacts my dive that much to chance.

 

[Walter]

But so much more than volume of gas is involved in tank choice.

True, but if I have the volume I need, I can make the rest work.

 

[Dan Gibson]

I still have a few metric designed road projects left over. A standard 12 ft lane is 3.6 m, not 3.5 m. That's a little over 2 inches difference. btw, FHWA approved the AASHTO metric Greenbooks, therefore it would not be substandard. I doubt you would win in court.

One problem with converting America to Metric would be construction. The difficulties in building roads based on metric plans were what finally killed the "forced" conversion of all highway projects using federal dollars.

For example: a standard highway lane is 12’ wide. That’s 3.658 meters. Most plans I saw used a 3.5 meter lane. That’s half a foot less. That means vehicles are a foot closer to each other on US Federal Metric Highways! If I were an attorney working for a client who had an accident on a federal metric highway, I would be emphasizing the fact that the highway was substandard based on AASHTO standards. My defense or claim would be based on the fact that the substandard highway contributed significantly to the accident.

There simply wasn’t any thought put into how to convert everyday article in common use. Do we use a hard conversion on a 2" x 4" beam? 50.8mm x 101.6mm? Or do we use a soft conversion? 50mm x 100mm? Is the 12" ID culvert going to be 304.8mm or is it going to be 300mm? Is the minimum sight distance along a road rated at 60mph (96560.83312166624333248666497333 kilometers per hour) going to be 182.88 meters or is it going to be 180 meters? 185 meters?

Converting to metric is far more than just learning to say meters instead of feet!
BTW - I’m classically trained as a scientist, too (chemist) and now have my own private practice as a land surveyor in California (hence my knowledge of making metric plans work on the ground).

 

[Benny-c]

Hi,

we use a metrical units and i would like to know, what volume unit do you use on your tanks. For the pressure is clear for me: PSI but for the Volume????? What do you see on your tanks graved???
Thank You very much

Don't Know were you got 'english units' from but metric is a simpler system from a diving perspective eg:
1kg Atmospheric pressure=1atm=Sea level pressure/0meters,
2atm=10metres(33ft)
3atm=20metres(66ft)
4atm=30metres(99ft)
etc.

For you non-metric users 1metre is a little more that a Yard

Benny