Simrad SP90
If you use a very small tilt (C) you will not be bothered by bottom
echoes. If the sea surface is gusty, you will however easily see
echoes from the waves. These echoes will normally be rather
weak, and will hardly move in relation to your vessel.
By means of a medium tilt angle (B) you will most likely be able
to pick up scattered fish or schools if these are located at some
distance above the bottom. The upper school in the illustration
will appear on the sonar picture before the bottom echo, while the
lower school will easily be disguised by the bottom echoes. Once
again you can activate the RCG function to improve the reading.
Noise and reverberation
Every time you use the sonar the quality of your search
operations will depend on numerous error sources caused by the
natural environment and physical properties of your vessel. We
distinguish between the two terms
noise
and
reverberation
.
•
Noise
is generated by the vessel: engine, propellers, winches,
refrigerating plants etc.
•
Reverberation
is caused by natural conditions in the sea:
temperature, salinity, sea state and bottom conditions.
The most common cause of acoustic noise is the propeller and
the cavitation caused by its rotation. Other typical noise sources
on board your vessels are winches, refrigerating plants, power
generators, pumps and cranes. If you experience problems you
think are caused by noise, try to find out which system that causes
the noise, and contact your dealer for advice.
Cavitation
As the propeller blades move through the water, low pressure
areas are formed as the water accelerates around and moves
past the blades. The faster the blades move, the lower the
pressure around it will become. As it reaches vapour pressure,
the water vaporizes and forms small bubbles of gas. This is
cavitation. When the bubbles collapse, they cause very strong
local shock-waves in the water. These may be audible and
can also damage the propeller blades. In addition to this, the
cavitation will generate very strong reverberation, commonly
seen as a red stripe of echoes behind the vessel.
If you have big problems with cavitation, try to adjust the
propeller pitch and/or the number of revolutions.
Reverberation
Reverberation is generated when the echoes from your sonar
transmission are reflected not only by fish and objects in the
water, but also from the bottom and the sea surface.
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Summary of Contents for Simrad SP90 Series
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