52 Sedan Bridge
(525 Sedan Bridge)
4.9
S
ECTION
4 • B
ILGE
& U
NDERWATER
G
EAR
C
OUNTER
-R
OTATING
P
ROPELLERS
(F
IG
. 4.9.1)
surface of the object. In the case of the propeller,
such damage is sometimes called a “burn.” It may
be caused by an irregularity in the propeller’s
leading edge, and it should be corrected by
reconditioning the propeller or by replacement.
Cavitation is a normal occurrence in modern sport
boats, and prop inspection should be part of routine
maintenance.
P
ROPELLER
T
ORQUE
AND
I
TS
C
ORRECTION
Some of the more powerful motors create a
considerable torque effect; that is, a twisting motion
causing the boat to ride with one sheer lower than
the other. This twisting reaction is caused by the
direction of propeller rotation lifting one side of the
boat. This causes an uneven drag, so that a boat’s
bow may tend to fall off in one direction or the other
from the intended course given by the wheel.
Torque action may occur when maximum or close
to maximum rated horsepower is applied. Any slight
torque may be offset by shifting passenger or gear
weight laterally to the high side of the boat.
C
OUNTER
-
ROTATING
P
ROPELLERS
On twin engine yachts, one propeller turns in a
clockwise direction while the other turns
counterclockwise in order to maintain a straight
course through the water.
When removing or replacing propellers, be sure to
install the correct propeller on the correct drive.
P
ROPELLER
I
NSTALLATION
:
For proper rotation, the installation of propellers on
inboard engine boats requires the right hand
propeller to be installed on the starboard side and
the left hand propeller to be installed on the port
side. Install in the following manner:
Step 1: Inspect shafts and propellers to ensure the
taper, keyways, keys, prop nut, jam nut and cotter
pin meet specifications. Special attention should
be paid when confirming key fit. Key must fit
snug in prop hub and propeller shaft. Key must
fit flat in bottom of both. If the key radius does
not match keyseat properly, stress risers and
catastrophic failure could occur.
•
Inspect propeller(s) to ensure the bore,
diameter and pitch meet specifications for
specific engine installation (diameter and
pitch are stamped on the side of prop hub).
Step 2: Dry fit the propeller on the taper without the
key and mark the position on the shaft with a
permanent marker. The distance between the
prop and the strut shall never exceed one (1)
shaft diameter.
P
ROPELLER
I
NSTALLATION
(F
IG
. 4.9.2)
JAM NUT
PROP NUT
KEY
SHAFT
D
C
B
A
D
C
B
A
E
G
F
E KEYWAY
COTTER PIN
PROPELLER
G
F
