Some means to reduce acoustic noise
Several factors are contributing to the performance of the hydroacoustic equipment used on board a vessel. Careful planning of the MS70 installation may reduce the acoustic noise.
Unfortunately, it is impossible to simply provide a number of specific procedures to reduce the noise.
An important factor is the physical location of the transducers. This depends on the vessel's design and construction, how the hull is shaped, and how the water runs along the hull. Other factors deal with other equipment mounted on board, and this will also be vessel dependant. At moderate ship speeds the machinery noise is usually dominant. At medium speeds the flow noise increases more rapidly and takes over, while at higher speed the propeller noise will be the main contributor.
Note
The information here must be considered as general advice. Each MS70 installation must be handled separately depending on the hull design and the other electrical and mechanical systems installed on the vessel.
Reducing flow noise
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•  The shape of the transducer (or dome around it) must be as streamlined as possible.
•  The hull plating in front of the transducer must be as smooth as possible.
Important
Be especially aware of bilge keels and zinc alloy anodes. The keel must be rounded off without sharp edges. Neither extruding objects nor abrupt transitions must be present.
•  The transducer must be mounted with a small inclination angle (approximately 2 degrees).
Reducing machinery noise
•  The transducer must be installed as far away from the engine room as possible.
•  The main engine and relevant auxiliary engines and equipment must be fixed to rigid foundations to avoid vibrations.
•  Any hull structure that may vibrate should 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 transducer must be installed as far away from the propellers as possible.
•  Sufficient clearance between the propellers and the hull, the rudder and the keel must be provided.
•  Place the zinc alloy 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.
Reducing electrical noise
•  Place the transducer cables in a metal conduit from the transducer to the Transceiver Unit. Terminate the conduit as close to the transducers and Transceiver Unit as possible.
•  Make sure that all units are properly grounded, as this is important to avoid electrical noise.
•  Use shielded cables with correct grounding.
•  Separate MS70 cables from other cables with high voltages, large currents or transients. Place all high voltage power cables in metal conduits.