Simrad PI, Installation Manual

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Simrad PI Catch monitoring system / Trawl hydrophone
10
851--164472 / Rev.B
Optimal location of trawl hydrophones
The most influential factors effecting hydrophone reception
common to most vessels are:
•
Noise from cavitation generated by the main propeller.
•
Air bubbles in the water around the hydrophone which
impede acoustic signals.
•
Noise from other acoustic equipment mounted in close
proximity.
If the shipyard or persons responsible for placement and
mounting the hydrophone(s) have knowledge and the proper
experience with installation of similar equipment, it should be
fully exploited when deciding where to locate the hydrophones.
This also holds true for adjusting the degree to which a
hydrophone should be tilted with regard to the both the vessel’s
physical characteristics and fishing method. Proper hydrophone
installation can increase overall system performance more than
any other single factor and therefore it is important that all the
variables involved be understood and taken into account. Often,
individual hydrophone installation requirements contradict one
an other and only an in-depth knowledge of the principles
involved can aid in deciding which should be given priority.
General rules-of-thumb
Although individual vessel vary greatly with regard to physical
construction and fishing methods, the following rules of thumb
apply under most circumstances.
•
Hydrophones should be located as far forward as possible,
normally one-third the length of the water-line from the bow.
•
If a vessel has a bow thruster, bubbles generated by its tunnel
can block sensor signals. Hydrophones therefore should be
either located forward of bow thrusters or far aft out of the
stream of bubbles found behind them. Vessels equipped with
bulbous bows can mount hydrophones in a specially designed
shoe on the after part of the bulb, forward of the bow
thruster.
•
The minimum distance a hydrophone should be located from
the main propeller is ten meters. Systems with hydrophones
mounted closer than this will have reduced range due to
underwater acoustic noise generated by propeller cavitation.
•
For trawlers that do not have to take a pursing wire into
consideration, hydrophones can be mounted in specially
constructed blisters offset from the vessel’s keel (preferably