Interphase Color Twinscope Operation Manual page 16

On inboards always mount the transducer
well ahead of the propeller(s). Turbulence
from props can seriously degrade performance.
(Thru-hull installation is recommended.)
d. Mount the transducer on the side of the hull where the
propeller is moving downwards. The upward motion of the
propeller generates pressure waves and pushes bubbles up
against the hull.
DO NOT install a bronze transducer housing directly into an
aluminum or steel hull because electrolytic corrosion will
occur. Consult your boat-yard for more information on how to
properly install transducers into these types of hulls.
IMPORTANT:
1) Make sure the water flow across the thru-hull transducer is
bubble and turbulence free at all speeds if good performance is
to be achieved.
2) Make sure the transducer has an unobstructed view of the
water ahead and below the boat.
3) On displacement-hull power boats, the transducer should be
mounted relatively close to the center line of the hull.
4) Mount the transducer in a place which has reasonable
access from inside the vessel since the transducer's bronze nut
will require tightening from inside the hull.
Because the Color Twinscope scans a 12 degree beam from
the surface ahead to directly below the boat, it is important to
make sure that the transducer is installed so that it will scan in
a vertical direction and not off to either side. The transducer
must be mounted so that it's bronze stem is as perpendicular to
the water line as possible. If necessary, use a fairing block to
properly position the transducer.
Use of a Thru-hull Fairing Block
Nearly all vessels have some dead rise angle at the transducer
mounting location. If the thru-hull transducer were mounted
directly to the hull, the sound beam would be tilted off the
vertical at the same angle as the dead-rise. Most thru-hull
installations will require a fairing block to insure the
transducer is mounted properly.
A fairing block is typically made of teak, mahogany, or plastic
and should be glued between the transducer and hull (both
inside and outside) to insure that the transducer's mounting
shaft is perpendicular to the water's surface. Make the fairing
block as smooth as possible, and not bigger than the
transducer's face, to minimize possible turbulence.
Mount Transducer so bronze stem is Vertical
Waterline
Hull
Transducer
Waterline
Fairing
Block
Hull
Boat's
Hull
16
Keep parallel
to waterline !
Forward
Bronze
Hex Nut
Keep parallel
to waterline !
Wood or
Plastic
Fairing Block
(Add sealing
compound
between
faring block
& hull).
Transducer