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Propulsion Train & Propulsion Train & Shaft Line Shaft Line
ComponentsComponents
IntroductionIntroduction
• Reduction Gears - fast to slow• Lubrication System - overcome
friction• Shaft components - turbines to the
working medium (ocean)• Propeller - transform rotational
energy into thrust
Reduction GearsReduction Gears
• Purposes– Allow turbine
and propeller to operate at most efficient speeds
– Combine two turbines to common shaft
Reduction GearsReduction Gears• Gear Types
– Straight• excessive vibration• low power-transfer
ability– Helical
• Reduces vibration, quieter
• Higher power transfer ability
• Excessive axial thrust– Double HelicalDouble Helical
• Two sets of teeth cut at opposite angles
• Eliminates axial thrust
Reduction GearsReduction Gears• Reduction Process
– Pinion (small) gear drives reduction (large) gear
– Reduction ratio = turns of pinion : turns of reduction gear
– Double-reductionDouble-reduction: reduction in 2 steps (more compact design)
– For naval reduction gears, normally 30:1
Reduction GearsReduction Gears• Locked TrainLocked Train
– Two sets of gears and shafts
– Torque transmitted equally
– Increases ability to transmit torque using smaller components
• Turbine shafts connected to reduction gears by flexible couplings to allow for thermal expansion
Shaft Turning/Jacking Shaft Turning/Jacking GearGear
• Electric motor that rotates reduction gears, turbines, and shaft w/o using steam– Cool down turbines
after operation– Prior to startup for
even heating– Position for
maintenance• Can be used to lock
shaft in place– In event of casualty
(i.e., loss of lube oil)
Shaft BearingsShaft Bearings• Designed to support
the moving parts of:– Shaft– Turbines
• Thrust bearings– Absorb axial forces– Ex: Kingsbury Thrust
bearing• Radial (Journal)
bearings– Absorb radial forces
Lube Oil SystemLube Oil System
• Provide lubrication and remove heat generated by bearings in overcoming friction
• Major components:– Sump– Pump– Strainer– Cooler– Bearings
Sump
PumpStrainer
Moving Parts
CoolerSW
Lube Oil SystemLube Oil System
• Lube oil can be kept in service for a long time if kept pure (two methods)
• Batch Purification– In-port only– Uses heated settling tank
• Continuous Purification– At-sea method– Centrifugal purifier separates oil &
contaminants
Propulsion ShaftPropulsion Shaft• Shaft is hollow: reduces weight &
increases resiliency• Consists of four sections
– Thrust shaftThrust shaft - from thrust bearing in reduction gears to end of engineroom
– Line shaftLine shaft - located in shaft alley (supported by line shaft bearings)
– Stern shaftStern shaft - part of shaft which penetrates hull (supported by Stern Tube bearings)
– Propeller shaftPropeller shaft - shaft connected to propeller (supported by Strut Bearings)
Propulsion ShaftPropulsion Shaft• Different sections needed for easy
installation, removal, & maintenance
PropellerPropeller• Made of hub and blades & creates the
thrust necessary to propel the ship through the water
•Terms:–Pitch:Pitch: axial distance advanced during one complete revolution of screw–Face:Face: the pressure side–Back:Back: the suction side
Propeller TypesPropeller Types• Constant vs. Variable
Pitch– Variable has the twisted
look– Adv: more efficient over
wide range of speeds• Fixed vs. Controllable
Pitch– In controllable, blades can
rotate on hub to change pitch (change direction)
• Right vs. Left Hand Screw– Viewed from aft of ship– Twin-screw ships have one
of each
CRP SystemCRP System
PropellerPropeller
• Cavitation– Formation and subsequent collapse of
bubbles as propeller turns– Occurs at critical speed
• Effects– Excessive noise– Erosion of blades– Decreased efficiency
Propeller Power vs. Propeller Power vs. Shaft RPMShaft RPM
• Flow RPM; Thrust (head) RPM2; Power RPM3
• So, if 10% power yields 100 RPM, how much power will produce 200 RPM?
10% x%1003 2003
x = 10 * (200/100)3
= 80% power80% power
Sample ProblemsSample Problems
• Shaft hP• shp=2πNT/33,000
• Effective hP• Propulsive efficiency• Slip ratio
QuestionsQuestions??