1. Propulsion Train & Shaft Line Components

2. Introduction Reduction Gears - fast to slow
Lubrication System - overcome friction
Shaft components - turbines to the working medium (ocean)
Propeller - transform rotational energy into thrust

3. Reduction Gears Purposes
Allow turbine and propeller to operate at most efficient speeds
Combine two turbines to common shaft

4. Reduction Gears Gear Types Straight Helical Double Helical
excessive vibration
low power-transfer ability
Helical
Reduces vibration, quieter
Higher power transfer ability
Excessive axial thrust
Double Helical
Two sets of teeth cut at opposite angles
Eliminates axial thrust

5. Reduction Gears Reduction Process
Pinion (small) gear drives reduction (large) gear
Reduction ratio = turns of pinion : turns of reduction gear
Double-reduction: reduction in 2 steps (more compact design)
For naval reduction gears, normally 30:1

6. Reduction Gears Locked 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

7. Shaft Turning/Jacking Gear
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)

8. Shaft Bearings Designed to support the moving parts of:
Turbines
Thrust bearings
Absorb axial forces
Ex: Kingsbury Thrust bearing
Radial (Journal) bearings
Absorb radial forces

9. Lube Oil System
Provide lubrication and remove heat generated by bearings in overcoming friction
Major components:
Sump
Pump
Strainer
Cooler
Bearings
Cooler SW
Moving Parts
Strainer
Pump
Sump

10. Lube 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

11. Propulsion Shaft
Shaft is hollow: reduces weight & increases resiliency
Consists of four sections
Thrust shaft - from thrust bearing in reduction gears to end of engineroom
Line shaft - located in shaft alley (supported by line shaft bearings)
Stern shaft - part of shaft which penetrates hull (supported by Stern Tube bearings)
Propeller shaft - shaft connected to propeller (supported by Strut Bearings)

12. Propulsion Shaft
Different sections needed for easy installation, removal, & maintenance

13. Propeller
Made of hub and blades & creates the thrust necessary to propel the ship through the water
Terms:
Pitch: axial distance advanced during one complete revolution of screw
Face: the pressure side
Back: the suction side

14. Propeller 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

15. CRP System

16. Propeller Cavitation Effects
Formation and subsequent collapse of bubbles as propeller turns
Occurs at critical speed
Effects
Excessive noise
Erosion of blades
Decreased efficiency

18. Propeller Power vs. Shaft RPM
Flow a RPM; Thrust (head) a RPM2; Power a RPM3
So, if 10% power yields 100 RPM, how much power will produce 200 RPM?
10% x%
x = 10 * (200/100)3
= 80% power

19. Sample Problems Shaft hP Effective hP Propulsive efficiency Slip ratio
shp=2πNT/33,000
Effective hP
Propulsive efficiency
Slip ratio

20. Questions?