The average difference in buoyancy of the same object in salt water versus fresh water is 2.5%. While differences in buoyancy of certain objects in saltier marine waters can be precisely measured, 2.5% is the generally accepted average difference.

If the average center body depth of a streamlined swimmer doing freestyle in calm seas is 30mm below the surface in fresh water, it seems plausible that the salt water center body depth would be 2.5% higher or 0.75mm higher (0.29 inches).

Over the course of 1 km, if a swimmer is riding 0.75mm higher in the water, with all things being equal between a fresh water and salt water swim (i.e., no currents, calm conditions, straight-line course, same energy output), we wonder how much faster would the swimmer be in terms of time in salt water vs. fresh water. Is there a reader in the open water swimming community who can provide an answer and explanation in scientific and layman’s terms?

Is there a reader in the triathlon community who can provide a similar answer and explanation comparing the relative speed of the same athlete over a 1 km course in fresh water vs. salt water who is swimming with a 2.5mm full body wetsuit?

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