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Fish Indications
Even using advanced sonar technology, it is sometimes hard to detect a
fish in the water. The body of a fish is just a little more dense than the
surrounding water. There is really nothing very solid for the sound waves
to bounce off of. The FishFinder L365 is very good at telling the difference
between a fish and the surrounding water. In fact, Raymarine is the
leader in this technology.
When the FishFinder finds a fish, it can be indicated by a fish symbol on
the display. In general, a larger symbol means a larger fish. This rule is
not always true, though. Let’s say that there are two fish of the same size:
one is close to the surface, and the other is near the bottom. The fish
which is close to the surface will have a larger symbol. This is because
the fish which is closer returns more of the sound waves back to the
FishFinder.
Actually, the sound waves are usually reflected by the air sac near the
center of the fish, and not by the body of the fish. The size of this air sac
is different for different kinds of fish. This can also affect the size of the
fish symbols on the display. A fish with a large air sac will produce a large
fish symbol, while a fish with a small sac will produce a small symbol.
The symbol also indicates which of the two frequencies was used to locate
the fish. If the fish was spotted by the wide 50 kHz beam, the symbol will
appear to be hollow. If the fish was detected by the narrow 200 kHz
beam, the symbol will be solid.
If the fish symbol feature is turned off, the FishFinder indicates fish in a
different way. See Fig. 3-5. An arch-shaped mark on the display usually
indicates a fish. Again, a larger arch usually indicates a larger fish.
Several arches together show a school of fish.
The return from a fish will have a different appearance, depending on the
frequency used. If a fish is spotted by the wide 50 kHZ beam, the arch will
be broad. When using the narrower 200 kHz beam, the same fish will
produce a narrower arch.
The shape of the arch is also affected by the speed of the boat. If you are
moving slowly, the arches tend to be longer. If the boat is moving more
quickly, the arches are short and peaked. If the boat is moving very fast, a
fish may be indicated by a single vertical line.
Operating Instructions