Simrad EC150-3C, Installation Manual

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Introduction to transducer location
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 EC150-3C installation
must be handled separately depending on the hull design and the other electrical and
mechanical systems installed on the vessel.
Related topics
Where to install the transducer, page 45
Installation summary, page 30
Mount the transducer deep
In order to achieve the best possible EC150-3C performance, mount the transducer as
deep as possible under the vessel’s hull.
There are several reasons for this recommendation.
Flow noise
Consider the situations when the vessel is unloaded, and pitching in heavy seas. The
vessel is riding high, and the bow may even be lifted out of the water. This will cause a
lot of air to follow the shape of the hull.
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.
Cavitation
Cavitation is the formation of small air bubbles close to the transducer face. The bubbles
appear because the local pressure becomes negative during parts of the acoustic pressure
cycles. The cavitation threshold increases with the hydrostatic pressure. The noise is
made when the bubbles implode.
Transmitting in air
The transducer must never be lifted free of the water surface. If the transducer is
activated when out of the water it may be damaged beyond repair. Mounting the
transducer at a deep position on the hull will in normally prevent this.
Simrad EC150-3C Installation Manual