Matsya
Contributor
Very basic and embarrassing question but I will never know if I don't ask !! What does "FSW" stand for in relation to depth?
What does "FSW" stand for?
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Feet of Sea Water or Feet of Salt Water. It is a unit of pressure, not distance. FFW = Feet of Fresh Water.
OP
Matsya
Contributor
Hey Walter,
Thanks so much.
Thanks so much.
Any time.
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OK ... and now that Walter has answered the question ... do you understand why a diver would want to specify depth in FSW or FFW, as opposed to "feet" ???ramsabi:
... Bob (Grateful Diver)
Hank49
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Uhhh....to pass the OW quiz?
opalobsidian
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ummm because how saline the water is affects buoyancy???
H2Andy
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well... not to ruin Bob's excellent question, but perhaps as a hint
ramsabi, when expressed in feet of salt water (FSW) one atmosphere = 33 feet
when expressed in feet of fresh water (FFW) one atmosphere = 34 feet
ramsabi, when expressed in feet of salt water (FSW) one atmosphere = 33 feet
when expressed in feet of fresh water (FFW) one atmosphere = 34 feet
Fish_Whisperer
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Good question, Bob.
Example: I was diving (site name, wreck, reef, or quarry), and was at 55', or whatever number of feet. When I was flying, I would often state that I was ____ feet agl. (above ground level, as opposed to, above sea level)
Example: I was diving (site name, wreck, reef, or quarry), and was at 55', or whatever number of feet. When I was flying, I would often state that I was ____ feet agl. (above ground level, as opposed to, above sea level)
nolatom
Contributor
H2Andy:well... not to ruin Bob's excellent question, but perhaps as a hint
ramsabi, when expressed in feet of salt water (FSW) one atmosphere = 33 feet
when expressed in feet of fresh water (FFW) one atmosphere = 34 feet
Our computers and depth gauges read only the pressure to get the depth, right? I assumed mine's set to salt water, and I'm actually 2-1/2 percent deeper than it says if diving fresh, since fresh water's less dense? I usually dive salt so don't think about this much.
Unrelated trivia: ships, like people, float higher in salt water. When entering a fresh water river from the sea, they have to calculate in advance how much the ship will "sink" when it enters fresh, so they'll still have enough depth of water and stay afloat. Fresh is 1.000, salt is 1.025 as I recall. If you look on the middle of the side of a cargo ship, you'll see the Load Line markings diagram--on the left are the "Salt" maximun allowed loads, and on the right side of the mark, and slightly higher up (and hence deeper ship draft) are the corresponding "fresh" ones. These marks were developed to keep ships from being overloaded and sinking at sea. Ultra-trivia: they're called "Plimsoll" marks, after the Brit who invented the concept.
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