Understanding The Sonar Display - Garmin GPSMAP 3005C Owner's Manual

The wide beam is helpful in shallow water, because it gives you a much wider
view of objects in the water, including areas beyond the sides of your boat. At a
30-foot depth, the wide beam covers the area of approximately a 20-foot circle.

Understanding the Sonar Display

One of the first things to understand about sonar is that the transducer sends a
beam down to the bottom of the water, much like the beam of a flashlight. The
beam starts small near your vessel and expands as it gets to the bottom.
The Sonar Page does not show a 3-D representation of the underwater
environment. Instead, the display is in two dimensions, much like if you took a
picture of an aquarium. Only the depth of the item in the water is shown.
The strongest sonar returns appear on your screen as the most intense solid
color (depending on your selected color scheme; red is the default). The weakest
returns appear as the less intense, less solid colors (blue is the default).
The bottom of the water is always going to be the strongest signal, and therefore
the most intense color. The bottom is the continuous, intensely-colored line
running across the bottom of the screen. The GPSMAP 3005C includes the latest
technology in interpreting bottom signals; it can see through fish, structures, and
thermoclines (shown in the weakest colors). However, large schools of fish or
dense structures close to the bottom can affect water depth return readings.
NOTE: If the GPSMAP 3005C is unable to track the bottom for any reason,
the digits in the depth window flash on and off to alert you that the unit is not
tracking the bottom.
At the top of the screen, you might see a grouping of intense colors. This area is
surface clutter, which can be caused by waves or any other sonar interference at
the surface of the water. Too much surface clutter can obscure your view of fish.
You can turn down the Gain setting to reduce this surface clutter.
GPSMAP 3005C Owner's Manual
Between the bottom and the surface clutter, the fish appear as arches. Actual
fish returns might not always appear as perfect arches, due to the speed, fish
orientation, or other conditions. You can turn on the Fish Symbols setting if you
want to see on-screen fish in a fish shape.
Fish Symbols Turned On
The strength of the sonar return can also help you interpret the hardness of the
bottom of the water. The thicker the bottom line, the harder the bottom.
Hard Structure
U S > U S
SING ONAR NDERSTANDING ONAR
Soft Structure
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