Review of Engine Shafting, Propulsion
and Transmission Systems
Key Considerations for Industry
By
Dag Friis
Bob McGrath
Christian Knapp
Ocean Engineering Research Centre
MUN Engineering
1
Scope:
 Components of the Propulsion System
 Where engine power goes
 Propeller types
 Propulsive efficiency
 Cavitation
 Selection Guidelines
 What can I do with my as-installed system?
 Testimonials and Simulations
 Conclusions
2
Propulsion and Shafting System:
 Is a massive “family” that includes:
 Main Engine
 Gearbox
 Shafting
 Shaft couplings
 Journal and stern tube bearings
 Propeller
 Must be designed to work in harmony
 Changes or problems with one component effect the entire
system
3
System Power Evaluation:
Indicated Power
Brake Power
Shaft Power
Delivered Power
4
Where Engine Power Goes:
Gear Losses
4%
Remaining
48%
Shaft
Losses
3%
Prop Losses
(thrust
deduction)
25%
PTO (if
applicable)
20%
5
Propeller Types:
 Fixed Pitch
 Least Expensive in initial cost
 Efficient for wide range of operations
6
Controllable Pitch Propeller:
 Controllable Pitch
 Great for multi-mode
operations.
 Engine RPM remains
constant while pitch is
varied for different loading
conditions, or both
simultaneously
7
Nozzles:
KORT
• Built Low Speed Efficiency
• Loses operational efficiency
when majority of time spent
steaming
RICE
• Built for Steaming Efficiency
• Multiple options by going
with either speed or towing
nozzle
Depends on application and how much clearance you have if
using a nozzle makes sense
8
Mewis Duct:
• Designed for vessels with poor inflow due to hull form
• Stabilizes water inflow to propeller. Uniform load distribution.
• Rotated fins pre-swirl the flow, generates higher load on propeller and
more thrust
• Guaranteed efficiency gains (when designed and optimized for vessel
and coupled with rudder technology)
9
Achieving Good Propulsive
Efficiency:
 The Power characteristics of the engine
have to be matched to the best possible
propeller characteristics for this
application.
 The main propeller characteristics are:





Diameter
Pitch
RPM
Number of Blades
Blade Area Ratio
10
Achieving Good Propulsive
Efficiency:
 The greater the propeller
diameter the more efficient
the propeller, i.e. choose the
largest propeller that can be
reasonably accommodated
in the available propeller
aperture.
Propeller clearances (inches)
Prop diameter (inches)
60
minimum
72
maximum
minimum
100
maximum
minimum
maximum
a
4.8
12.0
5.8
14.4
8.0
20.0
b
4.8
15.0
5.8
18.0
8.0
25.0
c
9.0
18.0
10.8
21.6
15.0
30.0
d
1.8
3.6
2.2
4.3
3.0
6.0
Cavitation:
 Cavitation occurs when the pressure
in an area of the propeller falls
below the vapour pressure.
 This results in bubbles or Cavities of
steam forming
 The problem is that when the steam
cavities collapse on the surface of
the propeller it leads to erosion of
the blade material
 Collapse also generates noise
12
Cavitation:
TIP CAVITATION
SHEET CAVITATION
13
Choice of Blade Area Ratio:
 The smaller the blade area ratio the higher the open water
propeller efficiency
 The choice is made on the basis of choosing the smallest
ratio that will give satisfactory propeller performance from
a Cavitation point of view.
14
Hull and Propulsion System
Interaction:
 Interaction Between Hull and Propeller
 Flow speed through the propeller (Wake fraction )
 Effectiveness of the thrust developed by propeller (Thrust
Deduction Fraction)
 Hull Geometry and Characteristics
 The higher the L/B ratio the better the flow of water to the propeller

Results in a more gradual change in direction of water flow



Lowers likelihood of flow separation and eddy making
Increases flow velocity through propeller
Results in more uniform flow velocity through propeller
15
Selection of Propeller
Characteristics:
 In order to be efficient, the propeller characteristics
have to be selected based on:
 Maximum Allowable Propeller Diameter
 Flow conditions at the propeller (hull form)
 Cavitation
 Operational Scenario
 Operating RPM (gear ratio)
16
Selection of Propeller
Characteristics:
 Propeller type has to be selected based on operating regime:
 Fixed Pitch is best suited to a single speed operation

Fixed Gear Fishery, i.e. Propeller Designed for Cruising Conditions
 Controllable Pitch when towing fishing gear

Nozzle can be detrimental for boats that spend a major portion of
their time steaming to and from the grounds due to the increased
drag at cruising speed
 Nozzle Propeller when towing fishing gear, and affordable


This is only likely to be the best alternative if the vessel spends most
of its time towing gear
Usually fitted with controllable pitch to optimize performance at
both operating conditions
17
What can I do with my as-installed
system?
 Have Clearance? Increase your diameter /decrease rpm(mind tip cavitation)
 No Clearance?
Alter pitch and gear ratio (mind cavitation)
 Clearance AND Pitch restricted?
Alter gearing ratio (mind cavitation and
prop loading)
 Reduce unnecessary hotel loads (extra deep freezes, clothes dryers, T.V.’s, cabin
lights, etc)
18
Testimonials:
64'11" RPM VS Fuel Economy
35
30
25
60" Diameter
20
GPH
66" Diameter
15
86" Diameter
10
5
0
0
50
100
150
200
250
300
350
400
RPM
86” diameter propeller achieving best fuel econ. and highest speed at lowest rpm
19
Testimonials:
Identical 34'11" Vessels, Speed vs Prop Diameter at 660 RPM
10
9
8
22" Diameter
7
6
Speed (kts)
26" Diameter
5
4
28" Diameter
3
2
1
0
0
5
10
15
20
25
30
Prop Diameter (in)
28” diameter propeller achieving highest speed at identical RPM
20
Simulations:
35’ fixed gear vessel:
• Altered as-built prop from 25” to 30” diameter
• Achieved 12% fuel savings per hour
65’ mobile gear vessel:
• Constrained in diameter due to as-built specs
• Achieved 2% fuel savings per hour by altering pitch
• Greater savings achievable by altering of gear ratio
21
Conclusions:
 Have your propeller checked by a qualified professional for suitability of Diameter,
Pitch, RPM, and Blade Area Ratio and resulting efficiency for your operation
 If you are towing fishing gear a significant part of the time, a controllable pitch and
possibly a nozzle propeller may be the best choice
 If you are not towing gear a well designed fixed pitch propeller is your best option
 Check that changing propeller and/or gear ratio makes economic sense for the
remaining vessel life.
 Time and money spent in R&D can save and even make you money in the long term,
but the analysis has to be done.
 Remember your decisions should make business sense.
22
QUESTIONS?
VS
23
Propeller Cavitation Design Chart:
24
Considerations for Outboards:
25
Propeller Design Chart:
26
Symptoms and Causes:
27
Nozzle Propeller:
 If flow separation occurs around the
nozzle one will get a significant
increase in drag, i.e. reducing the
efficiency of the nozzle-propeller
 Nozzle-Propeller diameter will be less
than for regular propeller, therefore
resulting a reduction in efficiency
28
Propeller Types:
29
Propeller Design Parameters:
The Optimal Open Water Efficiency:
 Rises with increase of Propeller Diameter
 Rises with increase of Propeller Speed of Advance
 This is governed by hull characteristics and its effect on
slowing of the water flow through the propeller disk (wake
fraction)
 Decreases as the Blade Area Ratio Increases
 Governed by cavitation avoidance considerations
30
Achieving Good Propulsive
Efficiency:
 The greater the propeller
diameter the more efficient
the propeller, i.e. choose the
largest propeller that can be
reasonably accommodated
in the available propeller
aperture.
Propeller clearances (inches)
 This is done by allowing for
reasonable propeller
clearances in order to reduce
likelihood of pressure pulse
vibrations being induced in
the local hull structure.
Prop diameter (inches)
60
minimum
72
100
maximum
minimum
maximum
minimum
maximum
a
4.8
12.0
5.8
14.4
8.0
20.0
b
4.8
15.0
5.8
18.0
8.0
25.0
c
9.0
18.0
10.8
21.6
15.0
30.0
d
1.8
3.6
2.2
4.3
3.0
6.0
31