Garmin GPSMAP 188C Owner's Manual

Also see for GPSMAP 188 Sounder: Declaration of conformity Declaration of conformity Owner's manual and reference guide Specifications

Contents

Garmin GPSMAP 188C Owner's Manual Manual pdf 95 page image

GPSMAP 188/188C Sounder Owner’s Manual 89U SING SONAR > SONAR TAB OPTIONSUnderstanding SonarThe transducer mounted on your vessel transmits sound wavestoward the bottom of a lake, stream, or seabed in a cone-shapedpattern. When a transmitted sound wave strikes an underwaterobject—such as the bottom, a piece of structure, or a fish—soundis reflected back to the transducer. The transducer collectsthe reflected sound waves and sends the data to the GPSMAP188/188C Sounder to be processed and displayed. The underwaterdata is shown on the Sonar display in the order that it is returned:first returned is the first on the display.Generally speaking, if the only thing between the transducer andthe bottom is water, the first strong return comes from the bottomdirectly below the transducer and sets the bottom level. Weakersecondary returns provide the detailed data. Stronger returnsdisplay in darker colors, with red being the strongest return.Understanding the Sonar DisplayOne of the first things to understand about sonar is that thetransducer sends a beam down to the bottom of the water, muchlike the beam of a flashlight. The beam starts small near yourvessel and expands as it gets to the bottom. Refer to “TransducerCoverage” for more detailed information.The Sonar Page does not display a three-dimensional representationof the underwater environment; the display is in two-dimensions,much like if you took a picture of an aquarium. Only the depth ofthe item in the water is displayed. The Sonar display does not showyou where an item is located horizontally in the water, as shown inthe drawings below. The fish is not directly above the tree in reality,but it can look like they are on the Sonar Page.20'10'1'Aerial View of the Water Sonar DisplayFishTreeTree