Introduction
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 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
Figure 6
A skewed trawl
A
A
B
B
C
C
(CD012221-008)
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.
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.
322482/B
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Summary of Contents for PI GEOMETRY
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