Simrad PI, Руководство по установке

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Installation manual
5
851--164472 / Rev.B
Propeller noise
A vessel’s main propeller is the dominant source of underwater
acoustic noise. When ever possible, hydrophone(s) should be
located as far a way as possible from the main propeller and
never closer than ten meters. Hydrophone(s) should not be
mounted in the direct acoustic path (line-of-sight) of the main
propeller unless absolutely necessary.
The primary cause of propeller noise is cavitation (small
bubbles generated by the partial vacuum created by the blades as
they pass through the water). The resulting underwater acoustic
noise from cavitation is normally weakest on the side of the
vessel were the propeller blades rotate toward the surface and
most pronounced on the side were they rotate toward the
bottom. Most vessels have clock-wise rotating propellers
resulting in their port sides being less effected by cavitation
induced noise than their starboard.
To minimise the negative effect of cavitation noise on
hydrophone performance, installation is generally recommended
as follows:
•
Single hydrophone - if only one hydrophone is to be
installed on a vessel with a clock-wise rotating propeller, it
should be located on the port side of the hull.
•
Dual hydrophones - if two hydrophones are to be installed,
they should be placed on either side of the vessel’s keel.
When in doubt about the best fore-and-aft location for
hydrophones, they can be placed at different distances from
the bow (for example the port hydrophone can be a little
further aft than the starboard, approximately three to five
meters for a thirty-five meter vessel). When trawling in both
deep and shallow water the hydrophones should also be tilted
differently with respect to each other. The hydrophone that is
closest to the propeller should have the greatest tilt and be
located on the port side of the hull for a vessels with
clock-wise rotating propellers.
Bow/sternthruster noise
Bow and sternthruster operation may severely effect
hydrophone reception. Hydrophone installation closer than four
meters to either is strongly discouraged.