Garmin Fishfinder 250 Owner's Manual

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Garmin Fishfinder 250 Owner's Manual Manual pdf 34 page image

26WhitelineThe Fishfinder 250/250C can help you to determine if the bottom is hard or soft. When the sonarsoundwaves are reflected back by the bottom, a hard bottom returns a stronger signal than a soft bottom.A thin whiteline indicates a softer bottom while a thick whiteline indicates a harder bottom. Normally, theFishfinder 250 uses a black line and the Fishfinder 250C uses a red line to show the point where watermeets the bottom. This line follows the bottom contour, along with any significant objects lying on thebottom. The unit uses the whitelinefunction to make this bottom layerinformation easier to distinguish.With the Fishfinder 250/250C,whiteline helps accentuate wherestrong signals are located, whichmake bottom type determinationeasier. The example to the rightshows the bottom return with andwithout the whiteline activated.See page 14 for more information.ThermoclinesOne of the unique features offered by Garmin isSee-Thru® technology. See-Thru® technology allows theFishfinder 250/250C to “see” through thermoclines andhelps locate fish where they live -- and fish love thermo-clines. A rough definition of a thermocline is a break inwater where the water temperature changes faster than inthe water above it. Thermoclines give weak returns and areshown as the weakest colors/shades (see pg. 11).)Whiteline can also help you to determine the type of bottom struc-ture that is displayed on the graph. By determining the hardnessof the structure, you can make a better informed decision on thetype of structure.Structure is hard—probably a rock or stumpStructure is soft—probably a mud pileOn the WaterWhiteline and ThermoclinesThermoclineWhiteline Turned OffWhiteline Hard BottomSoft Bottom