Does Sonar need to be submerged in water to measure depth? Just put new Lowrance 520-c on the Neptune. Turned on the the screen and the depth read 7.5 ft., only about 2 ft. from the transducer to the ground.
Sonar works by sending and receiving sound waves off of a contact. It measures the time it takes for the signal to return and calculates the distance. For all practical purposes, sound travels about 6 times faster through water than it does through air. Supposedly, some transducers can actually be damaged by operating them out of the water. It's best to test your transducer alongside the dock by measuring the depth and comparing it your reading. Don't forget to take into account your transducers height in relation to the surface and of course your boat's bottom!
Excellent point. Your unit should have a setting for keel off set.
When you get into the water, take the boat to a shallow spot (10 feet of less) Ancor up and once you are set, take a weighted line and drop her down, mark the water line, pull it out and measure. (Check your actual depth) Now enter your keel offset and you will be set up. Don't forget to do this, if you fish or dock in the skinny your boat will appreciate your knowledge of true depth