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Simrad ES38-18/200–18C Installation manual
Introduction
A single answer to the question "where to install the transducer" cannot be given.
The physical location of the transducer depends on the vessel's design and construction, how
the hull is shaped, and how the water runs along the hull. There are however a number of
important guidelines, and some of these are even conflicting.
Note
The information here must be considered as general advice. Each ES38-18/200–18C
installation must be handled separately depending on the hull design.
Mount the transducer deep
In order to achieve the best possible ES38-18/200–18C performance, mount the transducer
as deep as possible under the vessel's 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 cavitation.
Cavitation is the formation of small bubbles in the water close to the transducer face
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 it beyond repair. Mounting the transducer
at a deep position on the hull will in most cases prevent 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.
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