ENGINE POWER TRANSMISSION
TRANSMISSION IN VESSELS
Propeller shaft, tail shaft – The aftermost section of the propulsion shafting in the stern tube in
single screw ships and in the struts of multiple screw ships to which the propeller is fitted.
Propulsion shafting constitutes a system of revolving rods that transmit power and motion
from the main drive to the propeller. The shafting is supported by an appropriate number of
bearings.
Gears and clutches: For medium-speed engine installations in large ships (as opposed to
coasters or intermediate sized vessels) reduction gears are needed to permit engines and
propellers to run at their best respective speeds. Their use also permits more than one engine to
be coupled to the same propeller. Gearboxes are available from manufacturers in standard sizes.
Firms produce a standard range for different powers of single and multiple input, single
reduction gearboxes for medium- (or high-speed engines) in a number of frame sizes.
The input and output shafts for single input gears, may be either horizontally offset, vertically
offset or coaxially positioned. From the appropriate selection chart, using figures for engine
power, engine speed and reduction ratio (also Classification Society correction for ice if
applicable), the size and weight of the appropriate gearbox can be found.
Ship manoeuvring is of course improved with twin screws and this is an added safeguard
against total loss of power due to engine breakdown. The disposition of two engines and shafts
can sometimes be improved with the use of offset gearboxes. Normally twin screw propellers
turn outward when running ahead, i.e. when viewed from astern the port propeller turns
anticlockwise and the starboard propeller turns clockwise. (Inward turning propellers, tend to
make the movement of the stern unpredictable when manoeuvring and have given rise to other
problems.)
Figure 8.28 (a) Single piston servomotor (KaMeWa) (opposite); (b) Detail of KaMeWa S1
propeller hub Key to Figure 8.28a
,Reverse reduction gearbox
Reversing with the use of a gearbox, after reducing engine speed as necessary, means that
continually starting on cold air is avoided and less compressed air capacity is required.
Reverse/reduction gearboxes, like straight reduction gears, are also obtainable in standard
sizes, with manufacturers' charts for selection. Gear lubrication is by a self-contained system on
many sets. There are various arrangements possible for the shafts in a reverse/reduction
gearbox to suit the required location of the engine input or drive shaft and the driven or output
shaft. The sketch (Figure 8.29) shows a simplified, flat arrangement for ease of explanation.
,The drive from the engine input shaft to the counter shaft, is through teeth on the outsides of
both clutch housings, which are in continuous mesh. When the control lever is set for ahead
running, the control valve supplies oil pressure to the ring piston of the ahead clutch. When the
control lever is set for astern running, the control valve supplies oil pressure to the ring piston
of the astern clutch. When either clutch is engaged, its pinion provides a drive to the large gear
wheel of the driven shaft and the other pinion rotates freely.
Oil pressure required for clutch operation is built up by a gear pump driven from the input
shaft. Lubrication is by means of overflow oil. The propeller thrust on the driven shaft is taken
up by the thrust bearing. The driven (propeller) shaft, for ahead running, rotates in the opposite
direction to the drive or input shaft. For astern running, the driven (propeller) shaft rotates in
the same direction as the drive shaft. To stop the propeller shaft, the control is moved to the
neutral position and both clutches are disengaged.
Flexible couplings
Where a gearbox is fitted, a torsionally flexible coupling (Figure 8.30) is necessary between the
medium-speed diesel and the reduction gear. The coupling is necessary because the periodic
application and reduction of torque as engine cylinders fire in turn, tends to result in alternate
, loading and unloading of the gear teeth. The torsional vibration effect is sufficient to cause
serious gear tooth damage.
Flexible couplings may be installed as separate entities or in conjunction with air or oil operated
clutches. Flexible couplings may be built in a common casing with the clutch. Apart from
protecting the gears, flexible couplings, are also able to withstand slight misalignment. The
Gieslinger coupling shown in Figure 8.30 has a housing and hub connected by leaf springs,
which flex in service to absorb torsional effects from the engine.
Air operated clutches
Clutches which are not part of the gearbox, are usually air activated, with pads or linings which
make either radial or axial contact. The application force for the friction pads or linings, is
supplied by compressed air in a reinforced neoprene rubber tube. The compressed air is filtered
and moisture is removed by drains provided in the system. Air pressure is monitored and the
low pressure alarm is particularly important. Some form of rotary connection between the air
supply pipe and the clutch is necessary, with the valve controlling the air supply to the clutch
tube being operated by hand or remotely controlled by a solenoid or air pressure.
For a radial air operated clutch (Figure 8.31) the compressed air expands an actuating tube
around the outside of the friction pads. Inward expansion of the tube forces the pads into
contact with the friction drum. The transmission of torque relies on the air pressure and loss of
pressure would allow slip. The open construction of the clutch allows air access for pad cooling
and the expanding tube compensates for wear. Springs (not shown) are incorporated for
disengagement of the clutch, which is also assisted by centrifugal effect. This type of clutch has
been supplied in combination with a Geislinger coupling.
Axial air operated clutch
This type of clutch also uses a neoprene tube which is inflated by compressed air. Expansion of
the tube (Figure above) produces a sandwich action between friction pads and disc. The friction
disc or drum is spline mounted and therefore has axial float. The friction pads are also free to
float axially; being mated with teeth machined peripherally inside the casing. Springs cause
TRANSMISSION IN VESSELS
Propeller shaft, tail shaft – The aftermost section of the propulsion shafting in the stern tube in
single screw ships and in the struts of multiple screw ships to which the propeller is fitted.
Propulsion shafting constitutes a system of revolving rods that transmit power and motion
from the main drive to the propeller. The shafting is supported by an appropriate number of
bearings.
Gears and clutches: For medium-speed engine installations in large ships (as opposed to
coasters or intermediate sized vessels) reduction gears are needed to permit engines and
propellers to run at their best respective speeds. Their use also permits more than one engine to
be coupled to the same propeller. Gearboxes are available from manufacturers in standard sizes.
Firms produce a standard range for different powers of single and multiple input, single
reduction gearboxes for medium- (or high-speed engines) in a number of frame sizes.
The input and output shafts for single input gears, may be either horizontally offset, vertically
offset or coaxially positioned. From the appropriate selection chart, using figures for engine
power, engine speed and reduction ratio (also Classification Society correction for ice if
applicable), the size and weight of the appropriate gearbox can be found.
Ship manoeuvring is of course improved with twin screws and this is an added safeguard
against total loss of power due to engine breakdown. The disposition of two engines and shafts
can sometimes be improved with the use of offset gearboxes. Normally twin screw propellers
turn outward when running ahead, i.e. when viewed from astern the port propeller turns
anticlockwise and the starboard propeller turns clockwise. (Inward turning propellers, tend to
make the movement of the stern unpredictable when manoeuvring and have given rise to other
problems.)
Figure 8.28 (a) Single piston servomotor (KaMeWa) (opposite); (b) Detail of KaMeWa S1
propeller hub Key to Figure 8.28a
,Reverse reduction gearbox
Reversing with the use of a gearbox, after reducing engine speed as necessary, means that
continually starting on cold air is avoided and less compressed air capacity is required.
Reverse/reduction gearboxes, like straight reduction gears, are also obtainable in standard
sizes, with manufacturers' charts for selection. Gear lubrication is by a self-contained system on
many sets. There are various arrangements possible for the shafts in a reverse/reduction
gearbox to suit the required location of the engine input or drive shaft and the driven or output
shaft. The sketch (Figure 8.29) shows a simplified, flat arrangement for ease of explanation.
,The drive from the engine input shaft to the counter shaft, is through teeth on the outsides of
both clutch housings, which are in continuous mesh. When the control lever is set for ahead
running, the control valve supplies oil pressure to the ring piston of the ahead clutch. When the
control lever is set for astern running, the control valve supplies oil pressure to the ring piston
of the astern clutch. When either clutch is engaged, its pinion provides a drive to the large gear
wheel of the driven shaft and the other pinion rotates freely.
Oil pressure required for clutch operation is built up by a gear pump driven from the input
shaft. Lubrication is by means of overflow oil. The propeller thrust on the driven shaft is taken
up by the thrust bearing. The driven (propeller) shaft, for ahead running, rotates in the opposite
direction to the drive or input shaft. For astern running, the driven (propeller) shaft rotates in
the same direction as the drive shaft. To stop the propeller shaft, the control is moved to the
neutral position and both clutches are disengaged.
Flexible couplings
Where a gearbox is fitted, a torsionally flexible coupling (Figure 8.30) is necessary between the
medium-speed diesel and the reduction gear. The coupling is necessary because the periodic
application and reduction of torque as engine cylinders fire in turn, tends to result in alternate
, loading and unloading of the gear teeth. The torsional vibration effect is sufficient to cause
serious gear tooth damage.
Flexible couplings may be installed as separate entities or in conjunction with air or oil operated
clutches. Flexible couplings may be built in a common casing with the clutch. Apart from
protecting the gears, flexible couplings, are also able to withstand slight misalignment. The
Gieslinger coupling shown in Figure 8.30 has a housing and hub connected by leaf springs,
which flex in service to absorb torsional effects from the engine.
Air operated clutches
Clutches which are not part of the gearbox, are usually air activated, with pads or linings which
make either radial or axial contact. The application force for the friction pads or linings, is
supplied by compressed air in a reinforced neoprene rubber tube. The compressed air is filtered
and moisture is removed by drains provided in the system. Air pressure is monitored and the
low pressure alarm is particularly important. Some form of rotary connection between the air
supply pipe and the clutch is necessary, with the valve controlling the air supply to the clutch
tube being operated by hand or remotely controlled by a solenoid or air pressure.
For a radial air operated clutch (Figure 8.31) the compressed air expands an actuating tube
around the outside of the friction pads. Inward expansion of the tube forces the pads into
contact with the friction drum. The transmission of torque relies on the air pressure and loss of
pressure would allow slip. The open construction of the clutch allows air access for pad cooling
and the expanding tube compensates for wear. Springs (not shown) are incorporated for
disengagement of the clutch, which is also assisted by centrifugal effect. This type of clutch has
been supplied in combination with a Geislinger coupling.
Axial air operated clutch
This type of clutch also uses a neoprene tube which is inflated by compressed air. Expansion of
the tube (Figure above) produces a sandwich action between friction pads and disc. The friction
disc or drum is spline mounted and therefore has axial float. The friction pads are also free to
float axially; being mated with teeth machined peripherally inside the casing. Springs cause
