Posted by: Dan Sprague | March 14, 2012

Depth finders for your boat

Back in the “olden days” the depth was determined by using a hand held lead weighted line that was dropped over the side to measure how deep it was. It works very well. Today an electronic depth sounder determines the depth by measuring the round-trip time required for pulses of ultrasonic energy to travel from the boat to the bottom and be reflected back to the boat.

The controls on the depth finders, lets you change the frequency of the unit and the cone size of the unit so you can fine tune for shallow or deep water. The transducer for the depth finder, is normally mounted as a through-hull fitting, bonded to the inside of the hull, or on a transom mount.  The angle of the beam of the transducer should not be greater than 15 degrees from the vertical.

For inside hull mounts, the hull needs to be solid fiberglass, not with a core or other material in it. The cable from the transducer to the main control unit and screen is usually a tuned circuit and its length cannot be changed.

The information displayed is generally available in feet, fathoms or meters. A fish-finder is a depth finder that presents a visual elevation display of the bottom and shows blips where fish or objects are in the water above the bottom. They often have a cone setting for shallow and one for deep water.

Most fish and depth finders have a shallow water alarm and the more expensive ones have a color display that is more easily interpreted then just a gray scale display. They now have side scan units that let you see what is on each side of the boat.

A Depth finder can be one that just shows the depth, or they can be a fish-finder type that shows depth and a display of the bottom. These sure are easier than the hand held lead line.


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