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??