Re: Salt/Fresh water bouancy

[Subscuba <Subscuba@aol.com>]

Martin,

That's a good question. Since a depth gage only responds to pressure it
doesn't care what density medium it is placed in. However, if it is calibrated
for seawater and indicates 100 feet for depth then you would be at 100 feet in
sea water but in fresh water you would actually be at 102.6 feet ( seawater=64
freshwater=62.38), not a big difference, assuming my numbers are correct. From
a hull pressure viewpoint, the sub also would not care. However, to achieve
neutral buoyancy(I looked the spelling up!) in seawater the sub would have to
displace enough seawater to equal the sub's weight. If you then went into
freshwater you would displace less than the sub's weight due to the lower
density of freshwater and you would become negative, read that as sinking.
Ray's statement that you could be going deeper than desired is true. Actually
the density of seawater and freshwater also varies with dissolved materials,
temperature and other factors so achieving an actual neutral buoyancy is
difficult. I guess the modern nukes use an electronically controlled trim
system which dynamically adjusts the trim. The nuke people don't publish much
real data on their operating systems, I wouldn't.

Have fun,

Ken Martindale