Installation manual

Purse seine hydrophone installation

851-165187 / Rev.A

When not in operation, bow/sternthruster tunnels create

turbulence and hence underwater noise when a vessel is under

way. Also, as a vessel pitches in heavy weather, thruster tunnels

may fill with air or aerated water which can disturb hydrophone

reception when released. Hydr ophone installation should take

into regard the noise and down stream disturbances found

around and aft of thrusters.

Note: Hydrophone installation must take into regard the noise and

down stream disturbances found around and aft of thrusters.

Noise from protruding objects and other sources

The primary sources of underwater disturbance (other than a

vessel’s main propeller and bow/sternthruster) that affect

hydrophone reception are:

• Main or bilge keels

• Zinc anodes

• Cooling elements protruding from the hull

• Equipment such as sonar hydrophones and pitot tubes

• Sea chests

• Overboard discharges

• Dents in the hull

All appendages to the hull, indentations and pipe outlets are

potential sources of underwater noise. They may act as resonant

cavities amplifying noise at certain frequencies, create cavitation

or turbulence. Hydrophones should not be located in the vicinity

of such objects and especially not immediately aft of them.

Minimum distance to sonar and echo sounder

transducers

To avoid interference, PI54 hydrophone(s) must be installed as

far away as possible from other sources of underwater acoustical

energy such as active sonars and echo sounder transducers.

Hydrophones should be placed at least two meters from such

equipment when ever possible and distances of less than one

meter avoided. Hydrophones installed in close proximity to

underwater acoustical sources should be located as far aft as

possible from them, and most importantly, not be subjected to

direct (frontal) transmission from such equipment.

Drop keel

In the event the vessel is equipped with a drop keel, the

hydrophones should be mounted aft of it. The choice between

installing a one, or two hydrophone system should be based on

the same horizontal and vertical coverage requirements for

vessels operating under similar conditions with fi xed keels.