Ed wrote in news:jD4kg.73886$QU3.46747
@bignews8.bellsouth.net:

They work OK at 20Kts but not over 200ft deep unless
I am going about 8Kts then it will read to 600ft..



The trouble with deep is that sound travels so SLOW you get away before the
ping has time to go down that far and get back. What comes back is very
weak, at best. The other trouble is thermoclines at that depth. It's what
our subs hide behind so the "bad guys" lose them as the layers between
underwater layers of different temperature waters are quite impervious to
sonar sound, reflecting and absorbing the pings every time they go through
them. At long depths, you'll see the signal simply vanish, even though you
know the bottom's right where it was. The bottom at depth is also
undisturbed for millions of years. It's a soft composite of layers and
layers of whatever dies and falls to the bottom or what falls into the
water or what grows on the bottom. None of it is a nice, hard surface to
bounce pings off of.

If you ever meet a sub sonarman who's been at sea a while, ask him about
what the obstacles are. His sonar is HUGE with hundreds of transducers
listening intently for the sounds of the sea. He knows all the sea's queer
sound deadening phenomenon. I'm always in awe of their skills in hearing
and knowing what they hear in their profession. Those guys are some of the
most important on the boats.