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A single answer to the question where to locate the transducer cannot be given. It
depends very much on the vessel's construction, how the hull is shaped and how the
water runs along the hull. There are however a number of important guide lines, and
some of these are even conflicting.
Mount the transducer deep
Mount the transducer at a deep position on the hull. Consider the situations when the
vessel is unloaded, and when it is pitching in heavy seas.
There are several reasons for this.
1
The upper water layers of the sea contain a myriad of small air bubbles created by the
breaking waves. In heavy seas the upper 5 to 10 metres may be filled with air, and
the highest concentrations will be near the surface. Air bubbles absorb and reflect the
sound energy, and they may in worst cases block the sound transmission altogether.
2
Another reason to go deep is the cavitation in front of high power transducers.
Cavitation is the formation of small bubbles in the water due to the resulting local
pressure becoming negative during parts of the acoustic pressure cycles. The
cavitation threshold increases with the hydrostatic pressure.
3
The transducer must never be lifted free of the water surface. Transmitting into
open air may damage the transducer beyond repair. Mounting the transducer at a
deep position on the hull prevents this.
4
If the transducer is lifted up from the water during heavy seas, it may be damaged
when the hull strikes back at the sea surface. This is especially important for low
frequency transducers with large faces.
Mount the transducer away 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. Holes and pipe outlets are also
important noise sources. They may act as resonant cavities amplifying the flow noise
at certain frequencies. Do not place an echo sounder transducer in the vicinity of such
objects, and especially not close behind them. For the same reason, it is very important
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Where to mount the
Where to mount the transducer
transducer
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