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WHERE TO MOUNT THE TRANSDUCER
307120/B
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.
Another reason to go deep is the cavitation in front of
2
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 midway between the bow
and the stern to avoid heave effects
Heave is the up and down movement of the vessel. It disturbs the
echo traces in the echogram, so that a flat bottom is displayed
as a wave. A transducer location in the middle of the vessel
minimises the influence of vessel roll and pitch.
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
Where to mount the transducer
7
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