Humminbird 400TX Fish Finder User Manual


 
Wave action also affects the bottom depiction. The information drawn is a distance measurement,
so if the boat is moving up and down over flat bottom, the bottom depiction often appears in
regular variations that match wave timing.
Structure. Structure is defined as any object physically attached to the bottom. The sonar
configuration of the 400TX is optimized to give the most accurate depiction of bottom structure
possible. Grass, trees, stumps, wrecks or other debris are accurately displayed, however the
depiction of these objects varies with boat speed and direction. The best way to learn to interpret
structure is to operate the 400TX over a variety of known conditions and experiment with user
functions to best represent those conditions on-screen.
Surface Clutter. Surface clutter is the layer of water
near the surface that is rich in algae and other
growth, and often is aerated by wind or wave action.
This area of water interferes with sonar transmission
and often appears on-screen as regular clusters of
individual dots near the "0" line.
Thermoclines. Thermoclines are sharp differences in
water temperature. These are easily identified by the
continuous nature of the return.
Second Returns. When a sonar signal is reflected off
the bottom back to the transducer, there is often
enough energy left in the signal to be reflected off the surface of the water back to the bottom a
second time. Second returns appear as a slightly weaker bottom representation exactly twice the
depth of the primary bottom return. The second return is most likely to occur in shallow water and
in areas of relatively hard bottom.
Fish ID. The 400TX uses advanced signal
processing to further evaluate any sonar return
between the surface and the bottom. For instance,
a small school of bait fish usually appears as a
dense cluster of individual dots. If the return meets
certain additional criteria, a fish symbol will be
assigned. There are three different size fish
symbols used to indicate the intensity of the sonar
return. While signal intensity is a good indicator of
relative fish size, different species of fish have
different sonar characteristics, so it is not always
possible to distinguish fish size between varying
species. The signal intensity is "normalized" for
depth so that a small fish close to the boat does
not appear as a large fish symbol.
ID+ adds an additional piece of information to help the user locate fish. On selected fish symbols,
the digital depth of the designated fish is drawn to help locate the fish vertically. This is especially
helpful in setting bait depths or for downrigger operation.
The specific fish symbol indicates the type of sonar beam the fish is detected in. This gives you a
reliable indicator of side to side location relative to boat movement. Fish symbols which are
hollow are detected in the outside two beams. Hollow fish symbols facing to the right are in the
right beam and therefore are to the right side of the boat (as viewed from