f -> fsw -> msw -> m

[gcarter]

would someone please explain this paragraph to me? As I understand it, it makes no sense, so...


"The conversion between feet and meters of sea water is 1 fsw = 0.307 msw. This conversion is for the pressure units (msw and fsw), not the units of length,meter and foot which is : 1 ft = 0.305 m."

Relevant words highlighted.

 

[Thanshin]

One linear foot or 12 inches = 0.3048 Meters exactly (25.4 mm/Inch, as of July 1, 1959)
Inch - Wikipedia, the free encyclopedia

Therefore:
A: 1 FSW = 0.3048 MSW, not 0.307 MSW. Note that 1 FFW also equals 0.3048 MFW
B: 1 Linear foot equals 0.3048 Meters (not rounded to 0.305)
C: OK
D: OK

I can obviously agree with that (as C and D are mine and A and B from the manual, but what you're saying there is that the NOAA diving manual is just wrong.

Except in the quote of the OP the argument was that while 1ft = 0.305 m, 1 fsw = 0.307 msw, and never mentioned freshwater with a single letter...

I might be tired, but to me the quote of the OP seems to be just wrong tho.. If youre submerged 1 foot in seawater you are submerged 0.305 meters in seawater as well, and not magically 0.002 meters deeper because youre in the water instead of on land..

That's exactly the problem, yes.

a diver who is .305 meters below the surface of the sea will be subject to a slightly greater pressure. In fact, this pressure is .307 msw.

What you're saying there is that feet transform to "feet of salt water" in a relation of 1:1 but that doesn't apply to meters?!

I don't think feet, as a unit, have the inherent capability of always matching 1:1 with fsw while meters have a 0,305:0,307 relationship with msw.

For perhaps a bit more clarity, miles & kilometers are a measure of distance while mph and kph are a measure of speed.

Perfect example. Let me use it to illustrate my doubt:
- 1 m = 1.609344 kilometers
- 1 mph = 1.609344 km/h

Now imagine I say that 1m is 1.609344km but that 1mph is 2km/h.

one foot sides remain equivalent to .305 meters regardless of whether the container holds fresh or sea water. [...]And when we calculate the proportions, we find that 1 fsw is equivalent to .307 msw in terms of its weight.

Again, what you're saying there is that water is calculated in feet, giving a 1:1 relation between f and fsw, and then translated to meters, which gives 0,305m:0,307msw. As if feet were, somehow, the right way to measure water.



So, to wrap this up in a single question:

Is really, as implied by the quote, the relation between feet and feet of salt water 1:1, while the relation between meters and meters of salt water 0,305:0,307?

 

[Quero]

I can obviously agree with that (as C and D are mine and A and B from the manual, but what you're saying there is that the NOAA diving manual is just wrong.


What you're saying there is that feet transform to "feet of salt water" in a relation of 1:1 but that doesn't apply to meters?!

I don't think feet, as a unit, have the inherent capability of always matching 1:1 with fsw while meters have a 0,305:0,307 relationship with msw.



Again, what you're saying there is that water is calculated in feet, giving a 1:1 relation between f and fsw, and then translated to meters, which gives 0,305m:0,307msw. As if feet were, somehow, the right way to measure water.



So, to wrap this up in a single question:

Is really, as implied by the quote, the relation between feet and feet of salt water 1:1, while the relation between meters and meters of salt water 0,305:0,307?

No, I'm not saying that at all. If anything, it makes more sense to claim that I'm saying that there is a 1:1 relationship between meters and fresh water. In other words at one meter of depth of fresh water, the pressure is 1 mfw. When we convert to feet, what we get is that 1 foot of depth is equal to .305 mfw. Because salt water is denser and exerts more pressure at the same depth than does fresh water, at 1 foot of depth in sea water the pressure is .307

 

[Tortuga68]

Maybe this will help...

1 foot = 0.305 metres
0.305 metres of seawater = 0.0307 bar
0.0307 bar = 1 foot of sea water

 

[Tigerman]

I think what helps is to just say the OP quote is wrong (typoed) and that that the correct statement is that;

1 ft = 0.305 m
1 fet of saltwater (fsw)= 0.305 meters of saltwater (msw)
1 feet of freshwater (ffw) = 0.305 meters of freshwater (mfw)
1 feet of saltwater (fsw) = 0.307 feet of freshwater (ffw)

As long as both the medium and the the linear distance is constant I just cant see how the ratio between linear distance and pressure should somehow magically change and the OP quote who dont seem to make sense to the OP (nor me) indicates that the linear distance and the medium dont change.

 

[Thanshin]

Maybe this will help...

1 foot = 0.305 metres
0.305 metres of seawater = 0.0307 bar
0.0307 bar = 1 foot of sea water

It does help. So, you're saying that 0.305 metres of seawater = 1 foot of sea water. Which I agree with.

However, that would mean that the NOAA is simply wrong.
"The conversion between feet and meters of sea water is 1 fsw = 0.307 msw. This conversion is for the pressure units (msw and fsw), not the units of length,meter and foot which is : 1 ft = 0.305 m."

 

[Thanshin]

I think what helps is to just say the OP quote is wrong (typoed)

Indeed.

Which is kind of bothering, taking into account it's a unit conversion typo in a manual that's explaining at which depth you die.

 

[Quero]

The medium is not constant. Sea water and fresh water are different media with different densities and each exerts a different pressure given the same depth.

It's not a typo. It's a mental block that prevents you from comprehending the physics of the subject.

 

[Tigerman]

The medium is not constant. Sea water and fresh water are different media with different densities and each exerts a different pressure given the same depth.

It's not a typo.

IT IS!
The OP says 1 foot SEA water and 1 meter SEA water.. Go read it again..

 

[Quero]

It is not. The OP says only that 1 fsw = .307 msw. It goes on to say that the terms fsw and msw are pressure units rather than units of length. The fact that 1 foot of length equals .305 meters of length has no bearing. There is no typo.