Introduction To Transducer Location; Mount The Transducer Deep - Simrad ES120-7C Installation Manual

Where to install the transducer

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 ES120-7C installation
must be handled separately depending on the hull design and the other electrical and
mechanical systems installed on the vessel.

Mount the transducer deep

In order to achieve the best possible ES120-7C 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.
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