Controlling Corrosion; Propellers - Evinrude 4906B 4HP 1969 Owner's Manual

1-2 SAFETY
new to
A zinc prior
item will save corrosion
Most outboard engines have a flat area
on the back side of the powerhead.
the engine is placed with the flat area on
the power head and the lower unit resting on
the floor, the engine will be in the proper
al titude with the power head higher than the
lower unit.

1-3 CONTROLLING CORROSION

Since man first started out on the water,
corrosion on his craft
The first form was merely rot in the wood
and then it was rust,
forms of destructive
modern materials. One defense against cor-
rosion is to use similar metals throughout
the boat. Even though this is difficult to do
in designing a new boat, particularily
undersides, similar
whenever and wherever possible.
A second defense against corrosion is to
insulate dissimilar metals.
by using an exter ior coating of Sea Skin or
by insulating them with plastic
gaskets.
Using Zinc
The proper amount of zinc attached
boat is extremely important.
much zinc can cause wood burning by plac-
ing the metals close together
come "hot". On the other hand, using too
DIAMETER
Diameter and pitch are the two basic dimensions of
a
propeller. The diameter
a
circumference of circle
blades, as shown.
installation. This inexpensive
on
more valuable parts.
When
has been his enemy.
followed by other
corrosion in the more
metals should be used
This can be done
or rubber
to a
The use of too
and they be-
is measured across
scribed by the propeller
small a zinc plate will cause more rapid
deterioration
protect. If in doubt, consider the fact that
is is far better to replace the zincs than to
replace planking or other expensive
parts from having an excess of zinc.
When installing
two routes available.
different zincs on all metal parts and thus
run the risk of wood burning.
route, is to use one large zinc on the tran-
som of the boat and then connect this zinc
to every
internal bonding.
one zinc on the transom is the better way to
go.
Small outboard engines have a zinc plate
attached to the cavitation plate.
the zinc remains
times.

1-4 PROPELLERS

As you know, the propeller
what moves the boat through
This is how it is done.
ates in water in much the manner as a wood
screw does in wood.
into the water as it rotates.
the
between the blades and out to the rear in
the shape of a cone.
through the water in much the same manner
as a wood auger is what propels the boat.
the
Propeller
shear-pin, and nut, ready for installation.
of the metal you- are trying to
zinc plates,
One is to install many
underwater metal part
Of the two choices, the
with the engine at all
The propeller oper-
The propeller "bites"
Water passes
The propeller "biting"
and associated parts in
metal
there are
Another
through
Therefore,
is actually
the water.
order, washer,