heeling or under way.
A water-box can be made from any material that can be
easily worked and lamented or attached to the hull, i.e.,
fiberglass, "PVC" or acrylic tubing or wood. Some
boatsmen recommend a short piece of 5 or 6 inch
diameter tubing. Naturally, the hull forms the bottom of
the box. The bottom edges of the box or tube must be
shaped to fit snugly against the hull, with epoxy or other
suitable cement used to hold it securely in place. You
also will need to make a tightly fitting lid with a hole for
the transducer stem or connecting wire. The transom
mount type transducer can be used if mounted to the
side of the box. Fluid in the "box" needs to have a
density similar to water. Care should be taken to use a
fluid that will not attack the hull material, and also a fluid
that will not create a dangerous hazard if by chance it
leaks into the bilge. Stay away from anti-freeze because
it will attack the epoxy transducer "window." Mineral oil
or glycerine are frequently used, or water may be used
providing it is drained prior to lay-up to prevent freezing
and checked occasionally for evaporation. Check the
liquid in the box if any difficulty occurs, since the fluid
may have leaked out. Wash the transducer with
detergent before installing to make sure the surface is
properly wetted.
Position your transducer as close to the hull as possible
at first. Then adjust the vertical position by 1/8-inch
increments over a 1/2-inch total. This will enable you to
determine experimentally the best position for maximum
depth readings and strongest return signal. This is
Important, since the pulses will tend to cancel or
reinforce within the water box as a function of the
distance between the hull and the transducer window.
THRU-HULL
INSTALLATION
(WITH
OPTIONAL
TRANSDUCER)
As we said, turbulence and air bubbles at the transducer
must be avoided as much as possible. This problem is
most common in planning hull powerboats. Generally,
the best transducer location on a planning hull is a point
well aft of where the hull enters the water when on a
plane.
"Thru-hull" is certainly the most common and most
permanent method of transducer installation. Generally,
the mounting is done by a professional, or by a boat
owner who has enough confidence and ability to drill a
hole thru the bottom of his hull. Never mount the
transducer on the bottom of the keel where it will be
vulnerable should you touch bottom. Also keep it at
least 72 inches outboard from the keel. On a flat-bottom
boat, the transducer is bolted thru a drilled hole and
bedded in marine caulking compound to prevent leaks.
Vessels with shaped hulls require custom carved "fairing
blocks" to keep the bottom surface of the transducer
parallel with the water surface. The silhouette of the
fairing block should be kept as small as practical to
minimize
drag
and
chance
of
being
damaged.
Remember, the more smoothly the water flows over the
transducer and fairing block, the less turbulence and air
bubbles will be generated.
Sailboats have a different set of problems. The thru-hull
transducer must be sufficiently outboard of the center
line to avoid sonic reflections from the keel. As a rule of
thumb, the average transducer has a cone angle of
approximately 10' off of a vertical line. If this puts the
transducer too far outboard, as might happen on some
narrow, deep-keeled hulls, the transducer might be
mounted ahead of the keel. If it is suspected that the
location selected for transducer mounting is a little too
close to the keel, try cheating a little on the clearance
angle by tilting the transducer by no more than five
degrees away from the keel. -The effect on sensitivity
and depth accuracy will be negligible. Remember the
transducer must always be underwater, regardless of
heel angle, for your depthfinder to function.
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