Accessory EquipmentHydrodynamic designed otter boards are used for midwater trawling. The fishing depth is usually controlled by means of a netsounder (netsonde) or depth recorders. As for other types of Trawl nets, catch sensors can be installed in the codend to give information about the amount of caught fish. Tension sensors can also be used in combination with balanced winches to guarantee a stable, optimal opening. Horizontal sonars and fish finding equipment is a prerequisite for successful operations.