Simrad ES38-12 - REV C, Руководство по установке, Страница: 11 / 46

Where to mount the transducer
Mount the transducer far away from the propellers
The propulsion propeller is the dominant noise source on most fishing vessels, research
vessels, merchant vessels and pleasure crafts. The noise is transmitted through the sea
water. For this reason, the transducer should be placed far away from the propeller,
which means on the fore part of the hull. Positions outside the direct line of sight from
the propeller are favourable. On small vessels with short distances it is advised to mount
the transducer on that side of the keel where the propeller blades move upwards, because
the propeller cavitation is strongest on the other side. The cavitation starts most easily
when the water flows in the same direction as the propeller blade, and that is to some
degree the case at that side of the keel where the propeller blades move downwards.
Mount the transducer far away from the bow thrusters
Bow thruster propellers are extremely noisy. When in operation, the noise and cavitation
bubbles created by the thruster make the echo sounder useless, almost no matter where
the transducer is installed. And when not in operation, the tunnel creates turbulence,
and if the vessel is pitching, the tunnel may be filled with air or aerated water in the
upper position and release this in the lower position. In general, all transducers must
be therefore placed well away from the bow thruster. However, this is not an invariable
rule. Certain thruster designs combined with its physical location on the hull may still
offer suitable transducer locations near the thruster. If you are in doubt, consult a naval
architect.
Mount the transducer with a slightly inclined transducer face
Ideally, the transducer face should be mounted in parallel with the sea surface when
the vessel is in normal trim, as this will provide the most accurate echo information.
However, it is also very important that the water flow over the transducer face is laminar.
In order to ensure laminar flow, the transducer face may be tilted slightly upwards in
relation to the water flow. This allows the flowing water to meet the face directly, and
assures laminar flow. The inclination angle must however be determined carefully. The
angle must be small on transducers with narrow beam angles. As a rule of thumb, mount
transducers with beam angles smaller than seven degrees with minimum inclination
angle. The smaller beam angle your transducer has, the smaller the inclination angle can
be. Ensure that you do not mount the transducer with a negative inclination angle. This
may cause turbulence under the transducer face, and reduced echo sounder performance.
Summary and general recommendations
Some of the above guide lines are conflicting, and each case has to be treated individually
in order to find the best compromise. Generally the propeller noise is the dominant factor,
and a recommended transducer location is in the fore part of the hull, with maximum
distance from the bow equal to one third of the total length of the hull at the water line.
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