Propeller Noise - Simrad 38-200 COMBI D - INSTALLATION REV A Installation Manual

Installation manual

Propeller noise

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.
Bow thruster propellers are extremely noisy. When in operation,
the noise and cavitation bubbles 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.
Therefore, an echo sounder transducer should be placed well
away from the bow thruster.
5
851-165215 / Rev.A