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The Single-Anode Sys-
Although zinc shaft col-
lars and prop nuts are
most common, a much
superior system is to
install a single zinc an-
ode (or a few electrically
connected together)
mounted on the hull to
protect each shaft/prop
assembly. (The rudder
should be included if it is
stainless steel or
bronze.) Install the an-
ode anywhere it can
"see" the prop and shaft.
The anode is through
bolted onto the outside
of the hull. Run a bond-
ing conductor from a
zinc-fastening bolt, on
the inside of the hull, to
the engine block. You
also connect to the shaft
log, the rudder stock (if
metal) and the prop
Bonding System
In fact, all the metal
components in the hull
(deck gear need not be
included) should be con-
nected to the zincs—
tanks, machinery, hard-
ware, and fittings. The
standard system is to
run a heavy or main
bonding conductor down
the length of the hull and
connect all the hardware
and fittings to that with
shorter bonding jumpers.
The zinc (or zincs) are
connected to the main
bonding conductor with
jumper wires, thus pro-
tecting all the bonded
hardware. Bonding con-
ductors should be sized
from Table 1.
Resistance in the bond-
ing system should not
exceed 0.01 ohms (Ω). Copper straps or tubing of the speci-
fied cross-sectional area are excellent. On wood and FRP
craft, the bonding co
ductors need not be
To hook up the rudd
stock, you simply ha
to use a slack bondi
strap/wire so the rud
can turn freely throu
90°. (A stainless hos
clamp makes a good
fastener.) To connect
the prop shaft, howe
you must use a shaft
brush. These cost
around $50 apiece a
last for years. They a
simple bronze or bra
plates or strips with
graphite "brush" on
end and several mou
ing bolt holes on the
other. The shaft brus
fastened to a bracke
the brush presses on
the shaft. (The whole
is very much like the
commutator brushes
inside an electric mo
tor.) The bonding wir
fastened to a lug on
brush and run to the
main bonding condu
tor. Make certain tha
all the electric conne
tions are clean and
tight. It's amazing ho
much resistance a lit
bit of corrosion or a
loose wire can produ
quite enough to mak
your zinc ineffective.
Single-Zinc Advantag
The beauty of the sin
zinc system is that y
have only one zinc (o
group of zincs) to ke
track off (two, or two
sets, on a twin screw
boat). Even better, b
cause everything's
bonded to the same
anode, all the fitting
will float at the same
potential; they'll be uniformly protected. With individual
zincs attached to different underwater fittings, some ite
Table 1 - Bonding Conductor Sizes
AWG - American
Length of Run Wire Gauge Diameter
less than 20 ft. 8 or larger just over 1/8-inch dia. 0.013
20 ft. to 40 ft. 4 or larger just under 7/32-inch dia. 0.033
40 ft. and over 2 or larger just over 1/4-inch dia. 0.052
Making Your Zincs Work
It takes some smarts to make zincs work.
1) You must install zincs to protect your boat's metal fittings or
2) The zincs must be in tight clean electric contact with the metal
components they're protecting. (If they're not electrically con-
nected to the bonding system or metal hull, they're useless.)
3) The surface of the zincs must be exposed to the water. You
can't paint a zinc anode ever! You want it exposed, and you
want it to corrode. (They're not called "sacrificial zincs" for noth-
If your
Daffy Dancer
's zincs aren't wearing away, they're either way,
way too large (unlikely); not in proper contact with the metals they’re
protecting; or they're painted over. In any of these cases,
's zincs would be useless.
Properly sized, the zincs on
Daffy Dancer,
or any boat, should last
about a year, at which time they'll be about half gone. You have to
remember to check the zincs whenever possible to see that they're
firmly attached and corroding properly. You also have to remember
to install new zincs at the beginning of every season. Forget, and
you'll likely end up replacing the prop or shaft instead—not sound
Locating Your Zincs
Zinc anodes should be located correctly for maximum effectiveness.
The following will serve as a general guide:
2 Zinc System:
1 each port & starboard about 33% or the WL (waterline) for-
ward of the transom
4 Zinc System:
2 each port & starboard, 2 about 20% of WL forward of the tran-
som & 2 about 53% forward of the transom
6 Zinc System:
3 each port & starboard, 2 about 16% of WL forward of the tran-
som, 2 about 42% forward of the transom, 2 about 66% forward
of the transom
8 Zinc System:
4 each port and starboard, 2 about 14% of WL forward of tran-
som (about 70% of beam out toward the bilge), 2 about 16%
forward of transom (on or near the keel), 2 about 42% forward of
the transom, and 2 about 66% forward of the transom.
Continued next p