The fathometer adds a third dimension to our position by indicating how far above the ocean bottom the ship rests. The hewn wood ship's wheel of old, attached to the rudder for directional control, is replaced by a helm with computer-fed data that automatically adjusts to our heading. Much of our research work depends on knowing the depth of the ocean beneath us and the contours of the seafloor below. A buoy's mooring line needs to be cut to an exact length depending on the depth we drop the old railroad wheels that anchor it. Sonar, or sound waves, are sent through the water and upon reaching bottom reverse and deflect upward toward sensors that time how long this sound transit takes.
Calculations using the transit time and the speed of sound through water indicate the depth.
A simple sonar simulation activity is easy enough to set up. Using a plastic shoebox as the ocean basin, create a sea bottom landscape with seamounts and plains using clay or Play-doh in the container. Cover the box with a lid cut from cardboard with holes punched into it about one inch apart in rows and columns. Use a plastic drinking straw as the size template. Remove the straw, measure the length of the submerged area and record that number on a data sheet.