Furuno TS-331A - Manual (Page 11)

1. OPERATIONAL OVERVIEW
3
1.2.3 Mounting the underwater unit on the trawl
Usually the underwater unit is fixed either on the head rope of the trawl or on the
belly just above the ground rope.
The advantage of the former position is that the underwater unit is held
horizontal almost throughout the towing operation and consequently a good,
stable image can be expected. Its disadvantage is that it is difficult to detect the
ground rope, especially in bottom trawling since the ground rope in the bottom
trawl becomes positioned farther back than the head rope. In mid-water and
pelagic trawls, the ground rope usually becomes positioned below the head rope
and hence the ground rope is easily detected with the underwater unit on the
head rope.
The underwater unit is typically enclosed in a “pouch” made of fine mesh netting
and attached to the head rope with ropes. The pouch is attached to a small
mesh net (smaller trawlers) with ropes to stabilize the underwater unit. (Smaller
trawlers may not require the small mesh net for stabilization.) The small mesh
net is attached to the trawl with ropes.
Underwater
Unit
Pouch for
underwater
unit
Small mesh net
Head Rope
"Pouch" made of
fine mesh netting
Underwater
Unit
Small mesh net for
stabilizing underwater
unit
Head Rope
Typical installation of underwater unit (for larger trawler)