Interphace ULTRASCAN PC90, Operation Manual, Page: 10 / 56

10
Thru-Hull Considerations
Thru-hull transducers are for boats that exceed 40MPH
and /or have inboard motors. Transducer placement
depends on boat size, speed, hull configuration and
sonar application. On displacement hulls, the
transducer is generally located between 1/3 and 1/2 aft
of where the bow meets the water line. This is the
farthest forward the transducer should be mounted. It is
important that the transducer be below turbulent aerated
water created by the bow and does not come out of the
water during normal operation or when the boat is
pitching in a seaway.
Make sure the transducer has a clear view ahead and
that there are no forward hull obstructions that can
cause any turbulence in front of the transducer.
Mount so the transducer(s) bronze stem is within ap-
proxi/- 5 degrees of vertical to insure scanning
in the proper directions. Most vessels will require a
fairing block to compensate for the angle (dead-rise) of
the hull.
Special Thru-Hull Mounting Considerations
On sailboats with a fin keel, the transducer is most
often placed at the leading edge of the keel and
sometimes faired into the keel. As this location may be
where the sling rests when hauling the boat, the
transducer may be placed on either side of the hull with
the foremost face of the transducer even with the
leading edge of the keel. Alternatley, the transducer
may be placed forward of the keel ahead of the lifting
strap location. This should not be ahead of 1/3 aft of
where the bow meets the waterline.
On planing hulls the transducer is typically placed near
the transom. This is to provide smooth flowing water at
the greastest speed. However, most planing hull boats
create transducer aeration when on plane regardless of
transducer location.
It should be noted that thru-hull transducers can effect
boat performance in two important ways. The first
concern is cavitation created by the transducer that
causes reduced engine performance by disrupting water
flow around the propeller. This is smoothed out by the
hull in some boats, but on planing hulls with the
transducer near the transom, the hull is not able to clear
the cavitation. The second concern is uneven drag on
smaller high-speed boats. This may occur when the
Suggested Thru-Hull Transducer Locations
Fin Keel
Planing Hull
Displacement Hull
L = waterline length
~ 1/3 L