Installation Principles

Door sensors need to be installed in pockets welded on trawl doors. Carefully read these installation principles before installing sensor pockets.

Note: For bottom trawling, install sensors on the lower part of doors.

Angle of Attack

The angle of attack is the angle of the door in relation to the towing direction. This angle is important for the efficiency of the doors. It varies between trawl door models, so refer to manufacturer to know the exact angle. The angle is usually from 25° to 40°.


	1. Angle of attack: 25-40° 2. Opening angle 25-40°

Opening and Elevation Angles

The opening and elevation angles depend on the pocket installation on the door.

The opening angle is the horizontal angle of the pocket in relation to the door. It should be between 25° and 40°. Opening angles should be in line with the angle of attack. You need to indicate the opening angle on Mosa2.

The elevation angle, or tilt angle, is the vertical angle of the pocket in relation to the door. It should be between 15° and 20°. The sensor must point toward the vessel: adjust the elevation angle based on the operational depth of the door during fishing operations.


	1. Elevation angle: 15-20° 2. Opening angle: 25-40°


	1. Elevation angle: 15-20°

The down sounder must have a roll angle of 25° in relation to the door. If not, the door will disturb the signal.

Roll Angles

Roll angle of the sensors depends on the tilt of the doors when fishing. If doors are straight during fishing, you can apply a roll angle of 90°. If doors are tilted inward during fishing, slightly roll the pocket so that lines of communication between the sensors stay aligned. If not, you will have sporadic spread readings.

1. Adapt roll angles of pockets according to the tilt of the doors.

Installing a Door Explorer on a Clump

The sensor must be installed on the port side of the clump so that the clump does not block the down sounding.


	The roll of the sensor must be 0°, so that the down sounding has an angle of 25° toward the port side. This way, the down sounding will not be blocked by the clump. Make sure the soundings toward port and starboard doors are not disturbed either.
	The sensor must have an elevation angle between 15° and 20° in order to communicate with the vessel. In the same way as for the doors, adjust the angle according to the depth of the clump during fishing operations.