Furuno FCV-1200LM Manuel d'utilisateur télécharger pdf (Page 69)

4-3

Bottom nature

The nature of the bottom is known from the intensity and length of the bottom tail. Generally,

when observing the bottom nature, the lower sounding frequency is used, the pulselength is set

to long, and the gain setting is not disturbed. In the hard and craggy bottom, the bottom appears

more reddish and with a long tail. However, the bottom with a sediment may give a short tail if a

low frequency sounding is used.

Rock base

Mud & sand

Bottom nature

4.4 Fish Schools

Fish quantity

Fish quantity can be estimated to a certain extent from fish echoes on the screen if fish school

size and fish school density are kept in mind.

Fish school size

Usually the size of fish echoes on the screen is proportional to the actual size of the fish school.

However, if two fish echoes appear at different depths with the same size, the fish school at

shallower depth is smaller because the ultrasonic beam widens as it propagates and a fish

school in deep water is displayed larger.

Size of

fish school

Small

school

Large

school

School depth

and sounding

time

Deep fish school sounding time

Shallow fish school sounding time

Fish school size Difference of fish school sounding times

1 2 ... 64 65 66 67 68 69 70 71 72 73 74 ... 93 94

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Furuno FCV-1200LM Manuel d'utilisateur Page 69