Think of a transducer as your fishfinder’s mouth and ears. It shouts into the depths with its “ping,” and then listens for the echo. The type of transducer you use will have a tremendous impact on how your fishfinder performs, yet we tend to take the stock unit that comes with a fishfinder and assume it’s best for our uses. Bad move. Here’s why.
The size of the “crystals” in a transducer determine how well it will work. These crystals are actually piezoceramic elements (a polarized barium titanate or lead zarconate titanate disk or ring, coated in silver), which both create and detect vibrations. The larger they are, the louder they shout—and the better they can listen. In fact, when other factors such as output power and receiver quality remain the same, doubling the transducer crystal’s diameter has the exact same effect as quadrupling the fishfinder’s output power. So obviously, upgrading to a larger transducer can pay big dividends.
Transducer quality isn’t the only factor to consider, however. Mounting choices can have just as dramatic an effect on how well your fishfinder works. On most modern boats you’ll have three choices: shoot-through, through-hull, and transom mounts.
Shoot-throughs result in a significant loss of power, and should be avoided unless you want a mere depth gauge.
Through-hulls usually offer the very best performance at all different speeds, since they’re subjected to the least amount of turbulence. On the downside, they also require you to cut a hole in the bottom of your boat.
Transom mounts offer good performance at slow speeds, but often have a loss of detail and in some cases don’t work at all once a boat is on plane, because turbulence created by the hull, transom, and strakes causes interference. That said, if a transom mount is located and mounted properly, it should work fine at slow speeds and still offer 80- or 90-percent performance when on plane.
How can you choose which transducer is the very best to match up with your boat and your fishfinder? Some fishfinders, such as the new CHIRP units, will need specific types. Others can mate with a wider range. In either case, check out Airmar, the company that makes transducers for a wide range of marine electronics companies. Their “Transducer Finder” will point you in the right direction—and now you’ll know why.