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10 Transducers for Fishfinders
Thru-hull Transducer and In-hull Transducer
Similar consideration should be given to the location of thru-hull and
in-hull transducers. Figure 1-4 shows the best transducer location for
different hull types.
• Displacement hull powerboat – Locate at 1/3 aft load waterline
length (LWL) and 6 - 12" (150-300 mm) off the centerline on the
side of the hull where the propeller is moving downward.
• Planing hull powerboat – Mount well aft, on or near the center-
line, and well inboard of the first set of lifting strakes to ensure
that it is in contact with the water at high speeds. Mount on the
side of the hull where the propeller is moving downward.
Outboard and I/O – Mount just forward of the engine(s).
Inboard – mount well forward of the propeller(s) and shaft(s).
Step-hull – Mount just ahead of the first step.
Boats capable of speeds above 25 kn (29 m.p.h.) – Review
transducer location and operating results of similar boats before
proceeding.
• Fin keel sailboats – Mount to the side of the centerline and for-
ward of the fin keel 1 - 2 ft (300-600 mm).
• Full keel sailboats – Locate amidships and away from the keel at
the point of minimum deadrise angle.
• Fiberglass Hulls – Since the hull absorbs acoustic energy, trans-
mitting through the hull reduces the sensor’s performance. Fiber-
glass hulls are often reinforced in places for added strength. These
cored areas contain balsa wood or structural foam, which are poor
sound conductors. If you cannot avoid locating the sensor over
coring, follow the instructions for Installation in a Cored Fiber-
glass Hull on page 29.
• Thru-hull Transducer Headroom– Allow adequate headroom
inside the vessel for the height of the thru-hull housing, tightening
the nuts and removing the insert. The minimum headrooms are:
With fairing: 10" (254 mm)
Without fairing: 12" (305 mm)
• In-hull Transducer – Find a location where the fiberglass is
solid:
There are no air bubbles trapped in the fiberglass resin.
There is no coring, flotation material, or dead air space sand-
wiched between the inside skin and the outer skin of the hull.