High altitude fresh water diving
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oh my, you really worded that as complicated as possible, didn't you?
After reading it four times, I still am not sure what the question is. I'll make a guess.
You wanna calibrate your depth gauge to account for the reduced density of water at higher altitudes? You're thinking is that the "less dense water" will screw up your gauge accuracy? Hmmm... I don't believe I've ever heard this question before. I have no idea what reduced atmospheric pressure will do to the density of water.
I only work with "high density water", at the bottom of the sea. Water's densest at its coldest liquid phase.
After reading it four times, I still am not sure what the question is. I'll make a guess.
You wanna calibrate your depth gauge to account for the reduced density of water at higher altitudes? You're thinking is that the "less dense water" will screw up your gauge accuracy? Hmmm... I don't believe I've ever heard this question before. I have no idea what reduced atmospheric pressure will do to the density of water.
I only work with "high density water", at the bottom of the sea. Water's densest at its coldest liquid phase.
The important thing is to have a depth gauge that can be adjusted to accomodate the reduced atmospheric pressure at the surface at altitude so that the needle really reads zero at the surface.
Assuming you can zero the needle on the depth gauge, the inaccuracy in the the depth gauge reading under the surface will be due to the differing densities of fresh water versus sea water. This is only about a 3% difference so if you are diving in fresh water at an indicated depth of 99 FSW you would actually be at about 102 ft. But the important thing is that the absolute pressure would still be 4 ATA and it's the pressure that is important, not the depth gauge reading.
Personally, I have never seen the need to reference anything to feet or meters fresh water, as pressure is pressure and pressure is what counts. As long as the tables are calibrated in feet or meters sea water, everything works better if the depth gauge reads in feet or meters sea water.
The Cross corrections for theoretical ocean depth on the US Navy tables assume the depth gauge is reading in feet sea water, so no correction is required nor should the gauge reading be corrected to the fresh water value.
Assuming you can zero the needle on the depth gauge, the inaccuracy in the the depth gauge reading under the surface will be due to the differing densities of fresh water versus sea water. This is only about a 3% difference so if you are diving in fresh water at an indicated depth of 99 FSW you would actually be at about 102 ft. But the important thing is that the absolute pressure would still be 4 ATA and it's the pressure that is important, not the depth gauge reading.
Personally, I have never seen the need to reference anything to feet or meters fresh water, as pressure is pressure and pressure is what counts. As long as the tables are calibrated in feet or meters sea water, everything works better if the depth gauge reads in feet or meters sea water.
The Cross corrections for theoretical ocean depth on the US Navy tables assume the depth gauge is reading in feet sea water, so no correction is required nor should the gauge reading be corrected to the fresh water value.
You do not need to account for the difference in water density or depth. Your depth gauge is really reading pressure and then converting it to a depth. So the water pressure is the same whether you are at 100' in the ocean or 103' in the ocean. Since the tables are baased on water pressure (just reading depth), no compensation is needed for thefresh water.jap:
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