Installation manual

Simrad PI54

851-165187 / Rev.A

Optimal location of trawl hydrophones

The most influential f actors effecting hydrophone reception

common to most vess e ls are:

• Nois e 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. Pr oper 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 f i shing 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

1200 mm, but no less than 700 mm) to avoid turbulence. To