Simrad SC90, Installation Manual

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419050/B
The reverberation is caused by the transmission pulse itself and can only be reduced by
shortening the pulse duration or using a narrower beam width. The bottom reverberation
usually makes it difficult to investigate targets located close to the seabed.
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 SC90 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 SC90 installation
must be handled separately depending on the hull design and the other electrical and
mechanical systems installed on the vessel.
Reducing flow noise
• 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 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 should be damped or coated to reduce the
vibrations.
Simrad SC90 Installation Manual