Installation manual

Trawl hydrophone installation

851-165187 / Rev.A

also aid in reducing the effects of turbulence, hydrophones

should be installed as deeply as possible (pr eferably 600 mm,

but not less than 400 mm) from the vessel’s outer hull. When

ever possible, the distance from the keel to the bottom of the

hydrophone blister should not exceed 50 mm which can be

adjusted by countersinking the installation.

• Keel installation of hydrophones is recommended for

combined trawl/purse seining vessels that can not have

blisters projecting from their hulls.

On the starboard side of such vessels a purse seine

hydrophone can be installed together with a trawl

hydrophone.

• Hydrophones should have and unobstructed “view” of the

sensors attached to the gear, but not be located in the

line-of-sight of the main propeller.

• Hydrophones should be located aft of echo sounder

transducers or sonar installations, pref erable at a distance of

two meters or more. A proximity of less than one meter

should be avoided and hydrophones should never be subject

to their direct (frontal) transmission.

• Objects protruding from the hull will generate noise, the

areas aft of which should not be used to mount hydrophones.

• Thruster tunnels generate air bubbles which disrupt signals

from the sensors. The areas aft of thruster tunnels or other

sunken areas of the hull should not be used to mount

hydrophones.

• If there is any doubt about the f ore-and-aft positions fo r the

hydrophones, they should be located at different distances

from the bow (three to five meters relative to each other for a

thirty-five meter vessel). The hydrophone that is closest the

main propeller should be located on the port side of the

vessel.

• Hydrophones have a horizontal coverage of approximately

50 degrees. To maximise coverage using two hydrophones

they should be offset preferably 20 degrees outboard. With

this configuration the two hydrophones will overlap each

other by preferably 10 degrees and provide a total system

coverage of 90 degrees.

• Hydrophones have a vertical coverage of approximately 30

degrees. T he normal tilt angle is 20 degrees; if the system is

to be used in deep water the hydrophones should be tilted

preferably 30 degrees and in shallow water preferably 10

degrees. To maximise coverage using two hydrophones when