Kongsberg EM 122, Installation Manual

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Transducer arrays
Figure 3 Sketch of boundary layer underneath the vessel
The transducer arrays should therefore be placed far away from the propeller, which
means on the forward part of the hull. Positions outside the direct line of sight from the
propeller are favourable.
When a bow thruster operates, the noise and cavitation bubbles from its propellers may
make an echo sounder useless. Even when the bow thruster is not in operation, its tunnel
creates turbulence.
The tunnel may also drag air under the water, which escapes and make noise.
The transducer array should be placed with large distance from the bow thruster.
Noise from protruding objects on the hull
Objects protruding from the hull, such as zinc anodes, sonar transducers or even the
vessel’s keel, generate turbulence and flow noise. Also holes and pipe outlets are
noise sources. They may act as resonant cavities amplifying the flow noise at certain
frequencies.
Thus the transducer array should not be located in the vicinity of such objects, and
especially not close behind them.
Summary
Some of the above guidelines may be conflicting, and each case has to be treated
individually in order to find the best compromise.
317669/B
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