Simrad PI GEOMETRY - DATASHEET REV A Datasheet page 3

On the left trawl,
distance "A" on the
port side is longer
than distance "B"
on the starboard
side. The trawl is
unbalanced. On
the right trawl,
the distances are
identical. Measuring
the door spread
("C") will not detect
a distorted trawl
geometry.
(CD012221-008)
Why use the PI Geometry sensor system?
In order to maximize the performance
and the catch efficiency, the trawl and the
warps must be adjusted properly. This
is essential to ensure a square trawl and
minimum skew. This is also important
for danish seines, as the ropes must have
identical length.
Any disturbance to the trawl movements
may have a negative effect on the catch.
This is particularly important on a bottom
trawl. A skewed bottom trawl will result
in unstable bottom contact, and create
escape routes for fish below the gear
and through the side panels. On pelagic
trawls and danish seines a skewed net
will make the gear unstable, and the catch
be reduced. Optimal trawl geometry is
therefore vital for maintaining the catch
efficiency.
A trawl or danish seine may be skewed
C
A
B
for several reasons. Some of these reasons
are:
• Incorrect rigging of trawl, sweep
lines or trawl doors
• Misadjusted warp lengths
• Side current
• Towing in steep or sloped edges
If the rigging of the trawl is correct,
you can easily compensate for skew by
adjusting either port or starboard wire
length.
The PI Geometry sensor system is based
on the fact that a correct rigged trawl and
danish seine has exactly the same distance
measured from the centre of the headrope
or footrope to either door or trawl
wing. These distances must be identical
independent of weather conditions, sea
state or water currents.
C
A B
Advantages
Bottom and pelagic trawls:
• Measures if the trawl is skewed.
• Allows you to correct the trawl
geometry by adjusting the warp
lengths.
Danish seines:
• Detects variations in the distance
from the centre of the headrope (or
footrope) to either wing of the seine.
• Detects differences in the rope
lengths when the seine is closed
(distances between the wings should
then be close to zero).