L-3 Communications Navigation Echosounder LAZ 5100 - Manual (Page 13)

Page 2-1
L-3 ELAC Nautik
2 GENERAL INSTALLATION INSTRUCTION FOR ECHOSOUNDERS
2.1 TRANSDUCER INSTALLATION
The performance of an echosounder is limited by the acoustical propagation of sound in water.
Mainly this is influenced by the transducer mounting place, the operational frequency and the
transducer efficiency.
The transducer mounting place is to select in such a way, that the transducer surface is free of air
bubbles and turbulence. Air bubbles and turbulence will reflect the sound energy so that no echoes
from the bottom will return.
That's why transducers in general have to be installed in ship's bow.
If the ship has a bow thruster, the transducer has to be mounted ahead of it. Otherwise the
turbulence caused by the thruster hole will inhibit echosounding operation.
While the bow thruster is operating, no echosounding is possible because of the propeller rotation.
On ships with bulbs the transducer must be mounted as far ahead as possible.
Transducers mounted in ship's aft normally are limited in function during travelling, because this
area is very noisy. Due to engine noise, propeller rotation and air bubbles, the transducers are
only efficient during low speed travelling.
An indication for that is the disappearing of echoes, digital reading will indicate surface
reverberation ( 1-1.5 m ) or “?”.
While sailing only the front transducer should be used.
2.1.1 CABLE LENGTH, OPERATING FREQUENCY
Both the operating frequency and the length of cable between the echosounder and the transducer
influence the performance of echosounding.
General rules are:
At lower frequencies the influence of air bubbles and turbulence decreases, increased depth
measurements are possible, energy loss at longer cable length is minimised.
Higher frequencies are less sensitive against radiated water noise caused by the ships engine
and propeller rotation.
Following tables give information about echosounding performance depending on various
parameters.