[Public-list] depth sounder puzzle

[Gordon White]

I was out this weekend for the first time this season and everything 
seemed to work o.k - depth sounder, speed meter, auto pilot, etc. The 
depth sounder has always been a foot on the conservative side - reads 
six feet where there are actually seven from the surface. I checked this 
in the slip with a pvc pole with a small plate on the end so it does not 
go down in the mud and mislead me - Everything was fine.

    The depth readings just outside the slip were fine - 4.5 to 6 feet 
(actual depths 5.6-7) but about 150 yards down the creek the depth 
sounder began reading 1.5, 2. 1.5 feet. etc. Obviously it's not that 
shallow or I'd have been pretty hard aground. The actual dept in that 
stretch are 5.5 - 8 feet at that state of the tide.

    The shallow readings continued for 3/8 of a mile, then went back to 
what they should be and remained o.k. all day until I rerturned and in 
the same stretch of my creek (Moore's Creek off the Piakatank Rover)  I 
got extremely shallow readings in the same stretch. It read accurately 
when I got back in my slip.

Anyone have any suggestions? At first I thought it was a glitch in the 
instrument, but now I doubt that.

- Gordon White
Brigadoon II