Installing Sensor Pockets

You need to install pockets on each trawl door to hold the door sensors.

Before you begin

  • Read Installation Principles to become familiar with installation requirements.
  • You need different pockets depending on your type of door sensor:
    • Spread Sensor / Slant Range XL bottle
    • Mini Spread Sensor (stubby bottle)
    • Mini Spread Sensor (stubby bottle) with slim housing
    • Mini Slant Range (small bottle)

See Pocket Drawings to know which installation you need.

About this task

Important: Make sure you install the sensor pockets in accordance with the installation principles: pockets are important for the correct functioning of the sensors. If they are misaligned or if the pocket hides the sensor signal, you will have issues receiving data.
Important: We strongly recommend to have alignment bars inside the pockets to hold the sensor in the correct position.
Important: Take care to gather as much information as possible from the trawl doors manufacturer before installation. Such as the angle of attack and towing angle.
Note: If your door model have the doors rigged “nose up” or “nose down”, you need to change the angle of the door pockets so that the sensor always point toward the bottom of the ship when being towed.
Figure 1. Nose down (left) and nose up (right)
Note: If you use the sensors for bottom trawling, install pockets on the upper part of trawl doors. Make sure the pocket's position does not influence too much the center of gravity of the door. Refer to door manufacturer for details.

Procedure

  1. Use drawings of door pockets to mark the shape to be cut off: Pocket Drawings.
    Note: Ask your local Marport sales office for scaled templates of door pockets.
  2. Cut round openings in the doors.
  3. When setting up the alignment bar in the sensor pocket:
    Note: Master and Starboard sensors need to be oriented in a way they can communicate with each other. The alignment bar in the pocket ensures correct positioning. The housing of the sensors have a slot so they can be inserted in the alignment bar.
    • The alignment bar must be downwards on the port door (Master sensor).
    • It must be upwards on the starboard door, or clump (Slave or Clump sensor).
  4. Place the sensor pocket with the bottom portion sticking out of back side of the door. Adjust accordingly to the elevation angle and angle of attack you need (see Pocket Angle of Attack). Picture below shows angles of attack seen from above the door.
  5. You can trace a line with a marker around the pocket at the point it enters the door to remember the correct position.
  6. Spread sensors: Check if angles are correct:
    1. Weld only a few points on two sides of the pocket to hold it on the door.
    2. Open Mosa2 software.
    3. Activate and deactivate the water-switch to connect the sensor to Mosa2 via a wireless signal.
    4. From Mosa2, click the tab Pitch and Roll.
    5. Click Pitch and Roll Calibration then click Auto Calibrate. Pitch and roll offset values change according to the position of the sensor on the door. Pitch should be between 15 and 20°, roll should be ±5°. Roll may need to be higher depending on the door model and operation: adjust accordingly.
    6. If you do not have Mosa2 software, manually check the angles.
  7. If values are not correct, move the pocket, then check again.
  8. If values are correct, permanently weld the pocket to the door.
  9. We recommend to use a protective cage made of metal bars around pockets to protect sensors, like the examples below.
    Note: Make sure there is sufficient space between the protective cage and the sensor pocket, so that if the cage becomes bent, you can still remove the sensor.