FSW - What is this telling me?

[gcarter]

I see a lot of posts where rather than just say, for example 90 feet, someone will say 90 FSW. Other that telling me that it is in salt water, is there any other reason to use this convention?

It may seem like a silly question, but I honestly don't usderstand the reason for the convention.

 

[Kern]

Some dive in fresh water. Fresh water has different buoyancy characteristics to salt water. So some differentiate between the two.

 

[gcarter]

Some dive in fresh water. Fresh water has different buoyancy characteristics to salt water. So some differentiate between the two.

I get that. Just not sure it adds anything in most cases. If I am diving a quarry, it's a pretty safe bet it is fresh, and if I talk about reef diving, it is a pretty safe bet it is salt.

Maybe I'm just over thinking it.

 

[BabyDuck]

yes, but if you're talking about weighting, sometimes ffw or fsw is helpful, and so some people just get in the habit of differentiating.

 

[MauiScubaSteve]

I prefer to use "fsw/ffw" when ending a sentence, since ( .... 100 fsw. ) looks better to me than either ( .... 100'. ) or ( .... 100.').

 

[boat sju]

Maybe I'm just over thinking it.

You got it.

 

[gcarter]

You got it.

That's OK. I really don't mind looking stupid as long as I am learning something.

:bonk:

 

[PhuketPaul]

Hi

FSW is also used as a measure of pressure, not just your depth.

It also makes it clear for those of us used to using the metric system (Metres and Bars) what system you are using - very easy to miss the '

 

[ianr33]

I have a Uwatec bottom timer. It's calibrated for fresh water. (presumably because Switzerland is land locked?).
If I'm diving in the ocean it will read 103' (FFW) even though I am only at 100' (Actual depth,FSW)

Specifying what your computer/gauge is using makes it a bit more accurate although the practical difference is minimal.

Many/most? computers assume a dive at an altitude of zero feet is salt water. Dive a freshwater lake at sea level,or close to sea level, and the computer will assume you are in the ocean and give (slightly) inaccurate depths.
None of this has any impact on NDL calculations as that only depends on pressure.

 

[lamont]

Diving is all about pressure depth. All your dive tables are in fsw which is a pressure measurement.

You can continue to use your dive tables in fresh water just by keeping your gauge set to fsw even though you are diving in fresh water.

Similarly, if you dive in extremely brackish water with higher salt content and density, it doesn't matter that the 90 fsw your depth gauge registers does not correspond to the linear depth of water over your head -- your dive tables still work because its the pressure that controls your decompression or NDL limits.