Installing Electronics
by Don Casey
You have finally sprung for that new bit of electronic wizardry you've
been eyeing, and now you're wondering what else, besides what comes
in the box, you will need to get it installed. Usually, not much.
Mounting
The first challenge to installing electronics is finding a good mount
location. You want displays to be readily visible and dials and buttons
convenient to reach. A dry location is always preferable, even if the
unit is waterproof. Generally you should mount electronics high, meaning
up under the deck in sailboat, on the bridge of a powerboat. Be sure
there will be ample room at the rear of the unit for the wiring.
For a bracket-mounted unit, you will need a drill and the appropriate
bolts to install the bracket. Flush-mounting the unit through a panel
in the nav station or at the helm requires making an accurate cut-out.
The installation instructions in the box will provide the cutout dimensions.
Depending on panel material and access, you can make the cutout with
a saber saw, a rotary tool, or a keyhole saw. Be sure you know what
is behind the panel before sawing; it is all too easy to cut the wiring
to other equipment.
Antennas
As a general rule, mount a new antenna well clear of those already on
your boat. For maximum range, mount a VHF antenna as high as possible.
The range of SSB and ham radios is less dependent on antenna height,
so these antennas can be mounted near the deck. GPS antennas can also
be mounted near deck level, but they should have a clear view of the
sky, unobstructed by a top or rigging. Radar range and reception are
improved by mounting the radar antenna as high as possible. Keep in
mind that radar transmissions can damage eyes, so be sure this antenna
is well above head level.
A number of antenna mounts are readily available that will simplify
your installation. Some are screwed to a horizontal or vertical surface;
others simply clamp around a railing. A ratchet mount allows you to
fold the antenna down to reduce the vessel's vertical clearance.
Transducers
Transducers are the underwater component of depth sounders and speed
logs. They are generally mounted either through the hull or through
an underwater bracket attached to the transom. Depth sounder transducers
are sometimes mounted inside the hull to avoid fouling. This can be
a good arrangement, but it doesn't work well on some hulls.
Your boat will need to be out of the water to install a through-the-hull
transducer. Other than the trauma of drilling a hole through the hull,
transducer installation is straightforward.
Speed log transducers are mounted perpendicular to the surface of the
hull, and they can be located almost anywhere as long as they will always
be in clear (undisturbed) water when the boat is underway. That generally
means aft in a powerboat, and near the keel on a sailboat. They should
not be located directly behind another through-hull component or any
other hull feature that might alter the flow of water over the transducer.
Also pay attention to what is inside the hull where you want to install
the transducer.
In a solid laminate hull, you need only use a drill or a hole saw to
cut the appropriate size hole-designated in the installation instructions-insert
the cable through the hole, run a thick bead of polysulfide sealant
around the transducer just above the head, insert it into the hole,
and tighten the retaining nut inside the hull. Sealant should squeeze
out all around the transducer or you will need to remove it and apply
a thicker bead.
If your hull is cored, the process is more complicated. You must never
depend on flexible sealant to keep water out of the core. Rather, after
you have drilled the mounting hole, use a sharp tool to dig out the
core for an inch or so around the hole. Sand the inner surfaces of the
skins where the core was removed and wipe them with acetone. Fill the
space with a commercial epoxy paste such as Marine-Tex or with regular
epoxy thickened to a peanut-butter consistency with colloidal silica.
Let the epoxy cure for 24 hours, then run your hole saw through the
hole to clean it up. Now install the transducer exactly as described
above.
Depth sounder transducers should be installed perpendicular to the surface
of the water rather than the surface of the hull. In a sailboat, you
must also be concerned about the keel blocking the transducer's view
of the bottom when the boat is heeled, although this will not be a problem
under power or at moderate angles of heel. Transducers are sometimes
mounted forward of the keel. Dual transducers with a gravity switch
that activates the lower one are another option.
Mounting the transducer vertically may require wedge-shaped spacers,
called fairing blocks, both outside and inside the hull. Depth-sounder
are adversely affected by disturbed water, so the external block should
be smooth and streamlined. Also make sure the transducer is not located
behind a bubble-generating hull feature.
Transom mounts do not work in the disturbed water behind the prop of
an inboard boat, but if your boat is outboard or I/O powered, you can
limit new holes in the hull to just those required to screw the bracket
to the transom. If the transducer is to give accurate readings, it is
imperative that the bracket is absolutely flush with the bottom of the
boat-in effect an extension of the hull. Even then, turbulence at the
stern, especially at speed, can cause both log and depth sounder to
give inaccurate readings. Most transoms have a wood core, so take great
care to seal any screw holes you drill.
Signal
Wires
The wire from the transducer will have a connector that you simply push
or thread onto the appropriate connector on the back of the unit. Never
shorten the signal wires from transducers; if the wire is too long,
coil the excess.
Antenna wire can be RG8X coax if it is less than about 20 feet long.
For longer runs use RG8U or RG213U. Connectors (designated PL-259) need
to be soldered to coax, so if you don't have soldering experience, you
may want to get help with this part. Solderless connectors haven't done
well in the marine environment, although some new solderless terminals
may prove to be more durable. 
Power
Wires
Most 12-volt electronics come with either a red positive lead and a
black or yellow negative lead, or a pair of screw terminals marked +
and -. Hooking up the unit is essentially a matter of connecting the
+ lead to the + side of the battery and the - lead to ground.
But we don't normally connect electronics directly to the battery. Instead,
we take the power from the distribution panel. Since electronic equipment
can be sensitive to other loads on the circuit, it is a good idea to
give your new gear its own circuit. That means installing a new breaker
in the panel if you don't have an open one. If that is not practical,
then pick a lightly loaded circuit, one without electric motors or other
interference generators. Keep in mind that the breaker is protecting
the wiring, not the gear, so you cannot increase the size of the breaker
unless you know the size of every wire in the circuit.
Speaking of wire, you need #10 AWG, assuming the new unit is no more
than about 20 feet from the distribution panel. The exception to this
generalization is SSB, which needs bigger wire (#4). For longer wire
runs, consult the ABYC wire size table found in most electrical books
(including mine). Buy duplex safety wire with red and yellow conductors;
red is +.
Route the wire as high as possible-never through the bilge-and support
it with cable clamps at least every 18 inches. Where wires pass through
holes in panel boxes, bulkheads and other component, the hole must have
a grommet to protect the wire from chafe.
Use crimp connectors on the wire ends: step-down butt connectors to
join the supply wires to the light leads, ring connectors for screw
terminals, and flanged spades if the screws are captive. If you don't
already have a proper crimping tool, add one to your kit.
With the breaker off, connect the red wire to the output side of the
breaker. At the unit, connect this same wire to the lead or screw marked
+. Connect the yellow wire to the ground bus inside the distribution
panel-it will have black and/or yellow wires connected to it-and to
the lead or screw marked -. Double check the polarity, then flip the
breaker and turn on the unit. You should be in business.
For more
information about boat electrics, consult Sailboat Electrics Simplified
by Don Casey.
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