Force Vectoring Principles
Firstly, some very basic vector definitions:
The term vector is used to indicate a quantity that has both magnitude and direction
A vector is often represented by an arrow and a line segment. The length of the line represents the magnitude and
the arrow points in the direction of the vector
A vector can be split into components e.g. at right angles to each other
Vectors can be added together, subtracted and multiplied
For a system to be in equilibrium, the vector sum must be equal to zero
Now, applying these to trawling....
To position the trawl at a certain depth, the vertical component of the tension in the warp must be balanced by a
force acting in the opposite direction.
This required force Fv is the vector sum of the weight component of the device and the vertical component of the lift
generated by the device. The warp length and trawl speed are two variables which determine the required force.
To spread the trawl, an equal and opposite horizontal component of force Fh is required from each device. The trawl
speed and the fluid dynamic characteristics of the net determine the force required.
(To position the trawl laterally, while maintaining the same spread, the horizontal component of the one device must
be increased, while the horizontal component of the other device must be decreased by a similar amount.)
The vector sum of the vertical force Fv and the horizontal
force Fh gives the resultant force vector FR.
The length of this vector is equal to the magnitude of the lift
force that the device must generate, and the angle of FR to
the horizontal is equal to the heel angle of the device.
This is illustrated graphically on the left.
Thus, if the vertical and horizontal forces necessary to
position the trawl are known, the resultant force and heel
angle can be derived.
Below is a graph which typically illustrates the forces and heel angles required to maintain a trawl at a particular
depth. For example, for a depth of 500m the required resultant forces is 1300 kg and the heel angle -11 degrees.
.

Copyright Active Fishing Systems 2016

Active Fishing Systems

The Emerging Light in Fishing Technology

Active
Trawl
System