Kongsberg Simrad EK80, Installation Manual

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Where to install the transducer
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 EK80 installation
must be handled separately depending on the hull design and the other electrical and
mechanical systems installed on the vessel.
Topics
Mount the transducer deep, page 48
Avoid protruding objects near the transducer, page 49
Mount the transducer at forward part of hull to minimize the effects from the flow
boundary water layer, page 50
Keep the transducer far away from the propellers, page 51
Mount the transducer at a safe distance from bow thruster(s), page 51
Summary and general recommendations, page 52
Mount the transducer deep
In order to achieve the best possible EK80 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
Simrad EK80 Installation Manual