Transducer Location; Go Deep; Vessel Heave; Noise From Protruding Objects On The Hull - Simrad TRANSDUCER - INSTALLATION GENERIC REV H Installation Manual

Simrad Echo sounder transducers

TRANSDUCER LOCATION

Go deep

Vessel heave

Noise from protruding objects on the hull

6
A single answer to the question where to locate the transducer
cannot be given. It depends very much on the vessel's
construction. However, there are some important guide lines.
The upper water layers of the sea contain a myriad of small
air bubbles created by the breaking waves. In heavy seas the
uppermost 5 to 10 metres may be air-filled, with the highest
concentrations near the surface. Air bubbles absorb and reflect
the sound energy, and may in worst cases block the sound
transmission totally. Therefore, mount the transducer at a deep
position on the hull.
Consider the situation when the vessel is unloaded, and when it
is pitching in heavy seas.
WARNING
The transducer must never be lifted free of the
water surface.
Not only will the sound transmission be blocked, but the
transducer may be damaged by slamming against the sea surface.
Another reason to go deep is cavitation in front of high power
transducers. Cavitation is the formation of small bubbles in the
water due to the resulting local pressure becoming negative
during parts of the acoustic pressure cycles. The cavitation
threshold increases with the hydrostatic pressure.
Heave is the up and down movement of the vessel. It disturbs the
echo traces in the echogram, so that a flat bottom is displayed
as a wave. A transducer location in the middle of the vessel
minimises the influence of vessel roll and pitch.
Objects protruding from the hull, such as zinc anodes, sonar
transducers or even the vessel's keel, generate turbulence and
flow noise. Also holes and pipe outlets are noise sources. They
may act as resonant cavities amplifying the flow noise at certain
frequencies. Do not place an echo sounder transducer in the
vicinity of such objects, and especially not close behind them.
For the same reason, it is very important that the hull area around
the transducer face is as smooth and level as possible. Even
traces of sealing compound, sharp edges, protruding bolts or bolt
holes without filling compound will create noise.
851-160164/H