The net sounder is an echo sounder with a transducer mounted on
the headline of the net rather than on the bottom of the vessel.
Nevertheless, to accommodate the distance from the transducer to
the display unit, which is much greater than in a normal echo-sounder,
several refinements have to be made. Two main types are available.
The first is the cable type in which the signals are sent along
a cable. In this case there has to be the provision of a cable drum
on which to haul, shoot and stow the cable during the different
phases of the operation. The second type is the cable less net-sounder
– such as Furuno CN-24 - in which the signals are sent acoustically
between the net and hull mounted receiver/hydrophone on the vessel.
In this case no cable drum is required but sophisticated electronics
are needed at the transducer and receiver.
The display on a net sounder shows the distance of the net from
the bottom (or the surface), rather than the depth of water as with
the echo-sounder's hull-mounted
transducer. Fixed to the headline of the net, the footrope can
usually be seen which gives an indication of the net performance.
Any fish passing into the net can also be seen, allowing fine adjustments
to be made to catch the most fish possible. In other fisheries,
where the amount of fish in the net is important, catch sensor transducers
are mounted at various positions on the cod-end of the net. As the
cod-end fills up these catch sensor transducers are triggered one
by one and this information is transmitted acoustically to display
monitors on the bridge of the vessel. The skipper can then decide
when to haul the net.
Modern versions of the net sounder, using multiple element transducers,
function more like a sonar than an echo sounder and show slices
of the area in front of the net and not merely the vertical view
that the initial net sounders used.
We offer premier systems from
Furuno
* More
Data and Information on FishFinders
* More Data and
Information Transducers |
