Kongsberg Simrad CP200-5C, Installation Manual

Page: 49 / 110

484164/A
47
D
The converters transform the analogue echoes to digital format.
E Signal processing circuitry can create digital noise.
Related topics
Preparations, page 22
Acoustic noise, page 45
Self noise
Any vessel equipped with a hydroacoustic system (for example echo sounder or sonar) will
produce more or less self noise.
There are many sources of such self noise. It is necessary to analyse the different sources
of self-noise on a vessel, and find out how each source can affect the noise level of the
hydroacoustic instruments.
Machinery noise
The main contributor to machinery noise is usually the main engine on board the vessel. The
contribution from auxiliary machinery may, however, be considerable, especially if it is in
poor shape. The machinery noise can be transmitted to the transducer as:
• Structure-borne noise through the ship structure and the transducer mountings.
• Water-borne noise through the hull into the water to the transducer.
Electrical noise
Modern vessels are normally equipped with a lot of electric instruments such as
hydroacoustic systems, radars, navigation systems, and communication equipment. Any
electric instruments may in some cases cause electrical interference and noise. International
regulations and certifications are used to control and reduce this, but even these are limited if
the electrical systems are poorly installed and/or maintained.
Propeller noise
Propeller noise is often the main source of noise at higher vessel speeds. Variable pitch
propellers or fast moving propellers usually make more noise than fixed propellers or slow
moving propellers.
Propeller noise is usually water-borne. In some cases, however, shaft vibrations or vibrations
in the hull near the propeller may be structure-borne to the transducer. If a propeller blade is
damaged, this may increase the noise considerably.
Propeller cavitation is a severe source of noise. "Singing" propellers might be a source of
noise, which interferes at discrete frequencies. In some cases static discharge from the
rotating propeller shaft may be quite disturbing.
Preparations