Garmin GPSMAP 178C Owner's Manual

Also see for GPSMAP 178C: Specifications Flush Mount Template Manual Owner's manual

Contents

Garmin GPSMAP 178C Owner's Manual Manual pdf 121 page image

111Appendix GUnderstanding SonarUnderstanding SonarIf you are unfamiliar with basic sonar, or need help determining what is displayed on the graph,this section may be for you. This section is intended to help the novice user gain some understandingof how the GPSMAP 178C operates and how it can help improve their fishing productivity.To understand what the unit is displaying, it is important to have a general knowledge of how theunit works and how it determines what to display. Briefly described, the unit operates by transmittingsound waves toward the bottom of a lake, stream or seabed in a cone shaped pattern. When a transmit-ted soundwave strikes an underwater object such as the bottom, a piece of structure, or a fish, sound isreflected back to the transducer. The transducer collects the reflected sound waves and sends the datato the unit to be processed and displayed on the chart. The underwater data is displayed on the chartin the order that it is returned: first returned—first on the chart. The diagram in the sidebar demon-strates this showing an underwater scene as it would be displayed on the chart. Generally speaking, ifthe only thing between the transducer and the bottom is water, the first strong return comes from thebottom directly below the transducer. The first strong return sets the bottom level. Weaker secondaryreturns provide the detailed data. Stronger returns displays in darker colors, black being the strongestreturn. In Example 3 (page 113) you can see that the branches and the fish where the strongest second-ary returns are indicated in black on the display.That is brief description of how your GPSMAP 178C operates. Let’s take a look at how this data canhelp you to improve your fishing.This fish is currently in a dead zone and is not detected bythe sonar. The fish is in the coverage area of the transducer,but remember– the first strong return sets the bottom level.The fi sh is eventually detected when the first strong returnsets the bottom level below the fish.