Different Weight for Different Salt Water?

[Rick Murchison]

Note that Bermuda is in an area that's pretty salty... and deep...

Rick

 

[Charlie99]

A typical diver will need a 6 or 7 pound change in lead to move from fresh water to typical ocean water. 7 pounds for typical salinity of "35 whatevers" on that chart Rick posted. Or 1 pound for 5 of those salinity units. I only see a high of 37.5 somewhere in the mid-Atlantic and a 34 near the equator in the Pacific (ignoring the 33 in the arctic, since changing neoprene thickness overwhelms salinity changes). So that's about 3.5 unit change or 2/3 of a pound for the largest difference ocean waters in with normal circulation.

Rick's map doesn't have enough resolution to show areas like Sea of Cortez, variations in the Mediterranean, and the Red Sea, but if someone comes up with the data, the above simple sort of calculations show how much lead difference can be expected for a given change in salinity. Some data online seemed to indicate that although the Red Sea had an average salinity of 40ish psu, that the 1st hundred meters (where scuba is normally done) was about 37psu (practical salinity units). OTOH, another source said the Red Sea was 42psu. If it really is the very high 42psu on the surface vs the 35psu average value, then a typical diver would add about 1.4 pounds over ordinary saltwater.


Regarding the original poster, diving in Bermuda, I still stand by my assertion that I've seen bigger variations in lead weights, particularly when homemade out of scrap.

 

[CompuDude]

So what's the consensus here? Add a couple pounds for high saline areas (not talking about as high as the dead sea)?

 

[Rick Murchison]

So what's the consensus here? Add a couple pounds for high saline areas (not talking about as high as the dead sea)?

Consensus be damned! This is physics!
There is a correct and easily calculated answer, if you know a few things...
All you need to know is how much you and your gear weigh, what you need for neutral buoyancy where you are, the density of the water where you are, and the density of the water where you're going, and voilà! There you have it.
For example, if you go from California to the middle of the Atlantic there's a change of about 0.3% in density of the sea water (when it's at the same temperature... mustn't forget temperature...), and if you and all your gear weigh 300 pounds you'll need to add a pound in the Atlantic.
No consensus needed... it's just the way it is.
Rick

 

[The Kraken]

As I said.
Figger howzabout whaccha weigh with your fresh water rig and multiply it by 0.03, add that to your weight belt, with maybe one pound extra, and go dive.

Chances are you're already overweighted anyway.

the K