"Habda" wrote in message
...



If I am in what I know to be about 15ft of water... the depth that is
displayed numerically is like... 549ft or so... give or take a few 10ft.
If
I set the depth range to 30ft..... the terrain that is graphed on the
screen
is what I believe to be correct...

When you turn the unit on, does it come up in the last mode you selected, or
does it always start at some default?

It sounds to me like the gain is set too high for proper operation in
shallow water. If the unit is in a mode where it automatically selects the
appropriate depth range then it can easily get confused if the gain is too
high.

Here is what happens:

The transducer sends out a pulse of sound and then waits for an echo return.
The first echo it gets could be from the bottom, or it could be from a fish
swimming by so it will note the arrival time and keep listening. The longer
it waits represents a deeper depth, which also means that the expected
strength of the signal will be much less. To compensate for this the unit
will increase "turn up the volume" the longer it waits. The last echo that
it gets it considers to be the bottom, and it selects a depth range that is
appropriate.

If you are in shallow water and the initial gain is set too high, the unit
gets fooled by reflections. The original signal travels down and bounces
off the bottom. The returning signal is very strong because it hasn't had
to travel very far. This strong signal bounces off the bottom of the boat
and heads back to the bottom. A second bounce off the bottom and you get a
second reading that is twice the actual depth. This continues, giving you
echo returns at 1x depth, 2x, 3x, 4x, etc.

I know that I can get three bounces off of mine in an actual depth of 20
feet and off a very soft, muddy bottom. You seem to be getting 40 bounces,
which seems to be a bit much. Are you over a hard, rocky bottom?

If you are getting the bounces then you should see lines every 15 feet on
the graphical display. Of course, a line every 15 feet on a depth range of
600 feet would pretty much make the display a solid mass of lines.

So, long story short: turn the gain down. Or give it a clue by manually
selecting the depth range.

Rod