Avoid Protruding Objects Near The Transducer - Kongsberg Simrad C-All Installation Manual

Simrad C‑All Installation Manual
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 normally prevent this.
Slamming
Slamming happens if the vessel hull climbs out of the water in heavy seas. The force
of the water when the hull falls down can push the transducer up, and this may cause
damage both to the transducer and to its mounting. This is especially important for
low frequency transducers with large faces. The effect of slamming can be reduced by
mounting the transducer as deep as possible on the hull.
Note
Kongsberg Maritime AS takes no responsibility for any damages to the transducer, the
cable or the mounting arrangement, caused by slamming.
Related topics
Preparations, page 20
Where to install the transducer, page 33

Avoid protruding objects near the transducer

Objects protruding from the hull will generate turbulence and flow noise. This will
reduce the overall performance of your system.
Protruding objects may be zinc anodes, transducers or even the vessel's keel. Holes and
pipe outlets are also important noise sources, as well as rough surfaces caused by bad
welding. Even traces of sealing compound, sharp edges, bolts or empty bolt holes will
create noise. All these protruding objects may act as resonant cavities amplifying the
flow noise at certain frequencies.
Do not place a transducer near protruding objects, and especially not close behind them.
Make sure that the surface of the transducer face, the hull plating and putty around the
transducer is as even and smooth as possible. Mounting screws or bolts must not be
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