A few years back, I found myself approaching the entrance to New York Harbor in a thick fog. There was no way we were going to be able to spot the big ships going in and out, and it was doubtful that their radar was going to pick up our little 31-foot boat. The solution to the problem came from an unlikely place: our depth sounder.

MaptechBoating is a three-dimensional activity.By staying in 10 feet of water all the way around Sandy Hook and into the harbor, we were able to avoid trouble. It was plenty deep enough for us but way too shallow for the ships.

Boating is a three-dimensional activity. Knowing how deep the water is can keep you off the shoals, help you navigate, tell you how much scope the anchor requires and even where to drop it. That makes a depth sounder or fish finder an essential piece of safety gear on just about any boat.

While the term "sounding" is an ancient reference to determining depth, the modern electronic sounder literally uses sound to do the job. The display unit is attached to a transducer in the water, which can be thought of as a combination of speaker and microphone. It sends out a high-frequency pulse of sound, and then listens for the echo from the bottom. Knowing the speed that sound travels through water, it can calculate the distance to the bottom, and does so several times a minute to provide a continuous depth display.

CHOOSING A SOUNDER

As with all electronics, depth sounders – meaning both display and transducer – come in a wide array of price ranges, with varying capabilities and features. Some are designed to stand alone, some are combined with GPS and plotter, and some are part of large networked systems that include radar and other technologies. There are also portable units – even some hand-helds – that can be moved between the dinghy and the mother ship. On the very cutting edge – and priced accordingly – are units featuring "forward looking sonar" that collect soundings in front of the boat, though these have more to do with collision avoidance than collecting traditional depth information.

FurunoAbove, standard readouts offer numbers in black and white. Below, more complicated "fish finders" offer more information and a graphic look.
LowranceBasic displays give a simple black-and-white readout in feet, while more complex units – usually considered "fish finders" – offer programmable alarms and a full-color screen that indicates bottom contours and characteristics. Transducers are products unto themselves, allowing choices between metal or plastic; the more high level fish finders offer dual frequency or multiple frequency; and models that offer variations on the width and direction of the beam. These provide more sophisticated information.

SOUND(ER) INSTALLATION

Choosing a unit is often a matter of how you use your boat and how much you want to spend, but there are some basic rules for installation that can be considered universal.

Most people mount the display near the helm, for obvious reasons. Before you do, however, be sure to activate the unit and ensure that it does not affect the compass in that location. If you find interference, choose another spot. Also, never shorten the cable between the transducer and the display, because that cable is part of the unit's calibration. Simply coil up any excess and tuck or mount it out of the way.

The more difficult operation is installing the transducer below the waterline. The traditional installation involves drilling a large hole in the bottom of the boat while it is hauled out, then mounting and sealing the unit much like a thru-hull water intake. But there are alternatives. Smaller boats can use transom-mounted transducers, which are attached to the exterior of the hull. Boats of solid fiberglass can use "shoot through" or "in-hull" transducers, which are mounted inside the hull in a well filled with oil.