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Are in-hull transducers always less powerful than their through-hull equivalents? A. G. via e-mail
Airmar claims that its in-hull sonar units can find fish and bottom just as well as a comparable external unit, and, having seen the company’s obsessive testing regimes first hand (see column) I believe the claim. The benefits are appealing. Since the hull is undisturbed, there’s no chance that the transducer itself will cause aeration that might foul up its performance, particularly common at planing speeds, or that its protuberance will cause cavitation farther aft, like around the props. Plus there’s one less hole in your boat’s bottom to worry about, the transducer is not exposed to saltwater corrosion, and you can get to it easily if it needs tending anyway.

But there are caveats. In-hulls will not work in wood, steel, aluminum, or cored hulls. They can only shoot through solid fiberglass, and there’s a limit to that. The big R199, for instance, is rated to handle up to one inch of glass. In other words, an in-hull’s performance is affected by the hull, which is why you may have heard tales of reduced range when a conventional transducer is mounted inside. Airmar’s claims are based on the fact that its purpose-built in-hulls are engineered to offset the signal loss.

Whatever style of transducer you use, installing it right, and in the right place, is critical. Airmar is working with production boatbuilders to design transducer pockets right into their hull molds—a brilliant concept that includes adapter plugs such that most any through-hull transducer easily mounts flush—but, in the meantime, take care. That’s another good reason to know who Airmar is. Its Web site, www.airmar.com, and technical support personnel are standing by, ready to help.

Got a marine electronics question? Write to Electronics Q&A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282. e-mail: PMYElectronics@primedia.com. For fastest response, visit the Electronics forum at www.powerandmotoryacht.com. No phone calls, please.

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