Change water type?

[jhaifley]

Quick question, I tool the SDA diving for the first time yesterday. Everything worked great and I am very happy but I forgot to change the water type from salt to fresh. Unfortunately, myUemis won't let me edit that field of the dive, it is grayed out. Does anyone know how to fix that? I would hate for the dive to be inaccurate in the log.

 

[jhaifley]

Just to follow up and I submitted a ticket. Basically, the answer is no, there is no way to fix that. I wonder how much difference it makes to the calculations between fresh and salt. I don't recall ever setting that on other computers I have used.

 

[Marek K]

I wonder how much difference it makes to the calculations between fresh and salt. I don't recall ever setting that on other computers I have used.

I've wondered the same thing.

For a given pressure, you'd be a bit shallower absolute in salt water (denser) than in fresh water. But your computer (or depth gauge, for that matter) would show the same depth, and your computer wouldn't know or care whether it's salt or fresh water that's pressing down.

But it seems as though it wouldn't make any significant difference as far as nitrogen absorbtion... you'd absorb (or offgas) the same for a given pressure, salt or fresh. No?

The Oceanic/Aeris-type of hockey-puck computers adjust automatically at elevations higher than 2,000 ft, to display fresh-water depth... but I assume that's to accurately measure physical depth, rather than affecting any calculations.

 

[MarineResearch]

At standard surface conditions the densities of fresh and salt water are about 1,000 and 1,020 kg/m³, respectively. This is a pretty insignificant difference as far as calculating differences in pressure versus depth. However, it seems far more significant when looking at your personal buoyancy where your arse is about 98 percent water. In that case, the small difference in density has about a 50 percent impact on your weight requirements.

As already mentioned, pressure is the only real concern when it comes to nitrogen absorption.

 

[Vipa]

From the online manual...

"The type of water influences the depth measurement and associated screens and warnings."

I think it may also affect the skin cooling calculations as I would have thought fresh/salt water will have marginally different thermal conductivity properties?