What Is a Transducer on a Boat?

by Chris Stevenson
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A transducer serves as an antenna for a boat's sonar system. It turns electrical energy into a high frequency sound from a transmitter. A sound wave travels from the transducer through the water column and returns a signal, which it bounces off an object in the water. The returning echo from the object reaches the transducer; the transducer converts the sound, or ping, back into a readable frequency, which travels to the sonar's receiver. Transducers operate on the same frequency as the sonar unit, and can pick up very sensitive echo signals at various depths.

Transducer Crystals

Crystals, the active part of a transducer, contain man-made chemical materials of lead zirconate or barium titanate, which are mixed together and poured into a mold. The mold becomes heated by a furnace, which hardens the crystals. An electrical conductive coating is layered on both sides of the crystal. Wires are soldered to the coating, allowing the crystal to attach to a transducer cable. Crystals come in all shapes and sizes, with the round design most typical for sonar units. The crystal thickness denotes its frequency, and its diameter determines the cone or spread angle. For example; a cone angle of 20 degrees measures about 1 inch in diameter, while an 8-degree cone needs a crystal with a diameter of 2 inches.

Thru-hull Tranducers

Thru-hull transducers mount directly through a hole drilled though the hull. They often have long stems, or shafts, which are bolted with a large nut. Flat boat hull mountings remain simple, while hulls with V-shaped designs or off-angle contours require fairing blocks made out of plastic or wood to modify the transducer so it sits in a vertical position. Thru-hull transducers work well on inboard engine hulls, where the propeller, propeller shaft and rudder sit aft of the transducer, lowering interference.

Shoot-thru-hull Tranducers

Shoot-thru-hull transducers must be attached with epoxy inside a fiberglass boat hull. The echo sounds are transmitted and received directly through the hull structure and absorbed by the sonar receiver. Some of the depth range and sonar performance suffers from such a mounting configuration, as well as an adjustment loss for the best fish arches. However, the inside location of the transducer keeps it from being dislodged or knocked off from a submerged object. It functions well at high speed, since it does not create drag or friction. Shoot-thru-hull transducers resist all manner of fowling from kelp or seaweed.

Portable Mount Transducers

The portable type transducer generally has a smaller, compact size. It needs suction cups to hold it to a slick part of the hull's surface. Its advantage lies in its portability, since it can be easily detached and stored safely, or used on another vessel at a moment's notice. A few portable designs can be adapted to function with small electric trolling motors.

Transom Mount Tranducers

Transom mount transducers have to be mounted to the transom of the vessel, usually protruding below the bottom of the hull. Since the entire case must be submerged, they create some appreciable drag and do not function well at high speeds. However, they remain the most popular of the external transducers, since they can adapt to almost any hull design, with the exception of the inboard powered engine. They have exceptional sensitivity and depth range, especially while static and at low speeds.

Optimum Transducer Performance.

Transducers, made by several manufacturers, have undergone design changes over the years to improve their performance, sensitivity and accuracy. The best transducers are small, bullet-shaped and constructed with profiles that flow easily though the water. Cavitation, air bubbles that propagate from propellers, rudders, rivets and hull protrusions, give transducers false readings. Transducers are mounted strategically, where they have an even flow of water over their surfaces, with the least amount of disturbance. Transducers function best when mounted very low under the hull, away from cavitation sources, and must automatically "kick-up" when striking an object.

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