A control system for a towed object (1, 6; 20; 30; 50) in or on a body of water comprise one or more towing members (3) extending between the object (1) and a towing vessel (2). One or more ballast members (4) are movably connected to a respective one of said one or more towing members (3) and controllably movable at least a distance along its respective towing member. The towed object (1) may be controlled by moving one or more ballast members (4) on a towing member (3) in order to control the catenary (c) of a towing member (3). Individual ballast members (4) may be manipulated individually in order to correct, preserve or otherwise change the geometry of a trawl.

A control system for a towed object (1, 6; 20; 30; 50) in or on a body of water comprise one or more towing members (3) extending between the object (1) and a towing vessel (2). One or more ballast members (4) are movably connected to a respective one of said one or more towing members (3) and controllably movable at least a distance along its respective towing member. The towed object (1) may be controlled by moving one or more ballast members (4) on a towing member (3) in order to control the catenary (c) of a towing member (3). Individual ballast members (4) may be manipulated individually in order to correct, preserve or otherwise change the geometry of a trawl.

A method of controlling position of a trawl net is provided. The method may comprise: receiving, by a processor, a control input, wherein the control input comprises: (i) a selection of one of a plurality of position control modes, and (ii) a position control setpoint for the trawl net; receiving, by the processor, sensor data indicating a sensed position of the trawl net; generating, by the processor, a first trawl position control output based on the control input and the sensor data; determining, by the processor, a rate of change of bathymetry along a travel path of the trawl net; and in response to the rate of change of bathymetry meeting a threshold condition, generating a second trawl position control output by changing the one of the plurality of position control modes to another of the plurality of position control modes.

A method of controlling position of a trawl net is provided. The method may comprise: receiving, by a processor, a control input, wherein the control input comprises: (i) a selection of one of a plurality of position control modes, and (ii) a position control setpoint for the trawl net; receiving, by the processor, sensor data indicating a sensed position of the trawl net; generating, by the processor, a first trawl position control output based on the control input and the sensor data; determining, by the processor, a rate of change of bathymetry along a travel path of the trawl net; and in response to the rate of change of bathymetry meeting a threshold condition, generating a second trawl position control output by changing the one of the plurality of position control modes to another of the plurality of position control modes.

A method of controlling position of a trawl net is provided. The method may comprise: receiving, by a processor, a control input, wherein the control input comprises: (i) a selection of one of a plurality of position control modes, and (ii) a position control setpoint for the trawl net; receiving, by the processor, sensor data indicating a sensed position of the trawl net; and generating, by the processor, a trawl position control output based on the control input, the sensor data and predicted trawl net position data. The predicted trawl net position data may be generated by: defining, by the processor, a plurality of parameters; receiving, by the processor, input data comprising vessel speed data, tow line payout data, and a candidate drag coefficient value for the trawl net; and determining, by the processor, a tow angle based on the plurality of parameters and the input data.

A method of controlling position of a trawl net is provided. The method may comprise: receiving, by a processor, a control input, wherein the control input comprises: (i) a selection of one of a plurality of position control modes, and (ii) a position control setpoint for the trawl net; receiving, by the processor, sensor data indicating a sensed position of the trawl net; and generating, by the processor, a trawl position control output based on the control input, the sensor data and predicted trawl net position data. The predicted trawl net position data may be generated by: defining, by the processor, a plurality of parameters; receiving, by the processor, input data comprising vessel speed data, tow line payout data, and a candidate drag coefficient value for the trawl net; and determining, by the processor, a tow angle based on the plurality of parameters and the input data.

A spreading device for spreading gear, including fishing gear or seismic survey gear, towed behind a vessel in water, comprising a hollow body of concavo-convex shape and made of plastics material. The body has a general mirror symmetry about a plane which is substantially mid-height and/or mid-length in the body in use. The body has a fore-and-aft to top-to-bottom aspect ratio of between 1:2 and 4:1, and an inner concave side and an outer convex side. The device has a forward towing point on the inner concave side for a tow line to the vessel and aft towing point for attachment of the gear to be towed. The plastic material of the hollow body renders the body buoyant in water and enables ballast or additional buoyancy to be added.

A spreading device for spreading gear, including fishing gear or seismic survey gear, towed behind a vessel in water, comprising a hollow body of concavo-convex shape and made of plastics material. The body has a general mirror symmetry about a plane which is substantially mid-height and/or mid-length in the body in use. The body has a fore-and-aft to top-to-bottom aspect ratio of between 1:2 and 4:1, and an inner concave side and an outer convex side. The device has a forward towing point on the inner concave side for a tow line to the vessel and aft towing point for attachment of the gear to be towed. The plastic material of the hollow body renders the body buoyant in water and enables ballast or additional buoyancy to be added.