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ends of links 20 support swinging shaft 31. Gear 26 is
attached to shaft 31. Friction blocks 23 are held in
contact with the hubs of gears 25 and 26 by spring 24.
The propeller revolution indicator system (circuit
The friction blocks restrain the rotation of gears 25 and
K ) is used to indicate instantaneously and
26 and swing the links assembly, including shaft 31
continuously the revolutions per minute, direction of
and gear 26, in the direction of rotation of gear 25. This
rotation, and total revolutions of the individual
action engages gear 26 with one of the two gears 27,
propeller shafts. The information is indicated in the
the selection depending on the direction of rotation of
engine rooms, pilothouse, and other required
gear 25. Screws 80 limit the angular swing of the links
There are two types of propeller revolution
Gears 27 are secured to respective side shafts 35,
indicator systems, the synchro system and the
which also carry gears 29 and 69. These gears are
magneto-voltmeter system. The synchro system is
meshed and drive each other alternately, depending on
installed in large combatant ships and in many newly
which one of the two gears 27 is engaged with the
constructed small ships. The magneto-voltmeter
swinging idler gear 26. Gears 29 and 69 do not reverse
system is less complicated and is installed in small
when the propeller shaft reverses because idler gear
ships. Only the synchro system will be discussed in
26 reverses rotation each time it swings from side to
this training manual.
side. The same is true for gears 28 and 57 because they
are mounted on the hubs of gears 29 and 69,
A representative synchro-type propeller
respectively. Gear 57 engages gear 58, which is
revolution indicator system installed in a DDG is
mounted directly on the shaft of synchro transmitter
discussed in the following paragraphs. The system
37. The overall gear ratio between transmitter shaft 56
consists of transmitters, indicator-transmitters, and
and the shaft of the synchro transmitter is such that the
synchro shaft is always driven at twice the propeller
speed in a constant clockwise direction.
Revolution counter 38, which is driven at
The transmitters, one for each propeller shaft,
one-tenth the propeller speed, is driven through helical
indicate the revolutions of the propeller shaft. They
gears 28, 48, 47, and 30. The reading is directly in
also transmit the speed and direction of rotation of the
terms of propeller revolutions because each revolution
propeller shaft to the associated indicator-transmitter.
of the counter shaft registers a count of 10. Brake
The transmitters are installed on the actual propeller
shoes 50 prevent synchro transmitter 37 from driving
shaft usually near the reduction gear. They are
counter 38 backward during brief periods of rapid
electrically connected to indicator-transmitters
speed reduction.
located in their respective throttle stations.
The contact assembly is actuated by small
Figure 10-33 is the gearing diagram of a
insulating block 22, attached to one of the swinging
transmitter. The transmitter consists of a running
links 20. The block moves up and down as the link
synchro transmitter, revolution counter, and contact
swings with reversals of driving rotation. This action
assembly. These components, which are actuated by
moves center spring contact 44 from the bottom to the
suitable gearing, are mounted in a watertight housing.
top stationary contact 42, and vice versa. The center
The transmitter is either gear driven from the propeller
contact and one of the stationary contacts energize the
shaft or is directly coupled to the end of a stub shaft
signal lights in the remote indicator when the propeller
of the propulsion machinery, as required by the
shaft rotates in the astern direction,
particular installation. The synchro transmitter is
always driven at twice the propeller speed in a constant
clockwise direction.
The indicator-transmitter installed in each throttle
A drive worm, cut integral with shaft 56, meshes
station is used to convert the running speeds received
with worm gear 12, which is secured to shaft 14. The
from the associated shaft transmitters into angular
ratio is such that shaft 14 is driven at exactly one-tenth
synchro displacements, which are transmitted to the
the propeller speed. Gear 25 is attached to shaft 14,
various indicators.
and links 20 are free to swing on the shaft. The lower

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