ISYM Pair Trawl

Monitoring and control system for pair trawl.

Combined with modern radio technology Scantrol iSYM gives pair trawl skippers comprehensive information and possibilities for full automatic control of winches, engine power and steering.

Information from winches and navigation data are transmitted between the ships over a coded radio link and presented on the trawl screen on the partner ship. Interface to main engine control, propeller pitch, and autopilot are included to give the skipper the choice of having automatic control of net symmetry and vessel distance.

Pairlink comes in two versions, one with full autotrawl (Pairlink), and one that connects to other autotrawl systems via NMEA (Pairlink LT). The system can monitor one or two winches, and can be used with bottom and pelagic trawls.

Automatic Symmetry Control

The symmetry of the net is depending on the pulling power of the two ships. The most efficient way of controlling the net symmetry is to monitor the direction of the water flow and make sure the water flows directly into the trawl opening.

Pairlink can control the engine power automatically to keep the net symmetric by using information from a Scanmar symmetry or trawl speed sensor.

Winch Control

Wire lengths and wire tensions are transmitted between the two ships, and the data from the partner ship are immediately updated on the trawl screen. Also the length set points are transmitted to make it easy to see what the partner ship is doing.

The slave can choose to let the winches follow the master automatically. If the master changes the wire length, the slave’s winches will follow automatically.

Pairlink can monitor and control one or two winches for both bottom and pelagic trawls.

Vessel Distance

The distance between the vessels is calculated form the GPS positions transmitted over the radio link. The distance is displayed on the trawl screen, and the vessels positions are plotted. A warning can be activated if the distance is out of limits.

Pairlink includes an interface to the autopilot to allow automatic control of the vessel distance. The slave vessel can choose to follow the master at a constant distance.

Radio Communication

Pairlink includes a coded radio link with a range of 3000 meters. The frequency is 450Mhz, and there are 20 different channels that can be used to avoid interference from other pair trawl teams.

All data are coded by the transmitter, decoded and checked by the receiver. The transmission delay is less then one second.

Master- Slave Operation

The vessel that is identified as master can read information from the slave vessel.

The vessel that is set up to be the slave can read information from the master, and has the possibility to activate following automatic controls to follow the master: