Kongsberg Simrad MF90, Installation Manual

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Reducing flow noise
The shape of the hull plating around the installation trunk opening must be as streamlined as
possible. It is particularly important that the hull plating in front of the installation trunk
is as smooth as possible.
Important
Be especially aware of bilge keels and sacrificial anodes. The keel must be rounded off
without sharp edges. Neither extruding objects nor abrupt transitions must be present.
The fairing around the installation trunk must be streamlined. The transducer must be
protruding far enough down to reach out of the boundary layer.
Reducing machinery noise
The hull unit must be installed far away from the engine room. The main engine and relevant
auxiliary engines and equipment must be fixed to rigid foundations to avoid vibrations. Any
hull structure that may vibrate must be damped or coated to reduce the vibrations.
The use of shock absorbers or floating rafts may sometimes reduce this noise. The
structure-borne noise may be reduced by isolation, for example by providing vibration
clamping between the transducer and the hull structure.
Reducing propeller noise
The hull unit must be installed far away from the propellers.
Sufficient clearance between the propellers and the hull, the rudder and the keel must be
provided. Place the sacrificial anodes in places where the water flow is the least disturbed.
Ensure that the propellers blades are correctly designed and without damages.
The use of a baffle between the propellers and the transducer may reduce noise appreciably.
Static discharges caused by the rotating propeller shaft may be removed by proper grounding
or by mounting a coal brush from the shaft to vessel ground.
Reducing rattle noise
Ensure that no parts near the transducers can rattle as a result of water flow or vibrations.
Reducing interference
Interference from the transmission pulses from other hydroacoustic instruments on board
the vessel is difficult to avoid. The problem may be reduced by choosing the working
frequencies carefully and to some extent by separating the different transducers. On vessels
with a large number of separate hydroacoustic systems installed and in simultaneous use, a
separate synchronizing system (for example the K-Sync) should be considered.
Simrad MF90 Installation Manual