1 Introduction to R & P Resistance and Propulsion of Ships Propeller Geometry Introduction to R & P Basics Resistance and Propulsion of Ships Projected view of screw propeller from aft looking forward. Introduction to R & P Basics Resistance and Propulsion of Ships Propeller Diameter is D Introduction to R & P Basics Resistance and Propulsion of Ships Propeller Radius is R=D/2 Introduction to R & P Basics Resistance and Propulsion of Ships Propeller Hub Diameter D H Introduction to R & P Basics Resistance and Propulsion of Ships Direction of rotation Blade number Z b
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Introduction to R & P
Resistance and Propulsion of Ships
Propeller Geometry
Introduction to R & P
Basics
Resistance and Propulsion of Ships
Projected view of screw propeller from aft looking forward.
Introduction to R & P
Basics
Resistance and Propulsion of Ships
Propeller Diameter is D
Introduction to R & P
Basics
Resistance and Propulsion of Ships
Propeller Radius is R=D/2
Introduction to R & P
Basics
Resistance and Propulsion of Ships
Propeller Hub Diameter DH
Introduction to R & P
Basics
Resistance and Propulsion of Ships
Direction of rotation
Blade number Zb
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Introduction to R & P
Basics
Resistance and Propulsion of Ships
Leading Edge (LE)
Introduction to R & P
Basics
Resistance and Propulsion of Ships
Trailing Edge (TE)
Introduction to R & P
Basics
Resistance and Propulsion of Ships
Blade Face (pressure side)
Introduction to R & P
Basics
Resistance and Propulsion of Ships
Blade Back (suction side)
Introduction to R & P
Rake
Resistance and Propulsion of Ships
Propeller reference line yp is part of the prop coordinate system and is perpendicular to xp.
Xp is coincident with the shaft centreline
Profile showing rake
Introduction to R & P
Rake
Resistance and Propulsion of Ships
Rake is the axial distance from the generator line to the propeller reference line
The generator line (rake dautm) intersects the root section at midchord.
Propeller reference line yp is part of the prop coordinate system and is perpendicular to xp.
Xp is coincident with the shaft centreline
Profile showing rake
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Introduction to R & P
Blade sections
Resistance and Propulsion of Ships
Blade sections
If we intersect the propeller with cylinders of radius ri the intersection will be blade sections
Blade tip
Root section
Blade section at ri is often expressed as a fraction of the prop radius: r/R
Introduction to R & P
Blade sections
Resistance and Propulsion of Ships
Blade sections
Blade section near root (plan view showing section)
Blade section near tip (plan view showing section)
Expanded views of sections at different radii (this does not show pitch)
Introduction to R & P
Blade sections
Resistance and Propulsion of Ships
Illustration of blade sections on helicoidal surface.
Note that the pitch angle for each section is different: it decreases from root to tip.
Introduction to R & P
Blade sections
Resistance and Propulsion of Ships
Illustration of blade sections on cylindrical surface
Forward
Chord length
Pressure s
ide (face
)
Suction sid
e (back
)
Trailing edge
Leading edge
Illustration of expanded blade sections
Pitch datum line
Introduction to R & P
Pitch
Resistance and Propulsion of Ships
Outline of cylinder
Pitch
datum
Pitch angle φ
Centre line of cylinder
r
Blade section
Pitch
2 π r
The figure shows the helicoidal patch traced out by the blade section as it rotates through one revolution and advances forward.
To the right, the path is developed and we can see that over one revolution (2π r) the section advances a distance P, the pitch.
The pitch is determined by the pitch angle φ since we have assumed the section is moving along the path set by this angle.
Introduction to R & P
Blade section geometry
Resistance and Propulsion of Ships
Chord length
Mid chord (reference point) Chord line – passes through
LE & TE
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Introduction to R & P
Blade section geometry
Resistance and Propulsion of Ships
Maximum thickness
Section thickness
For the ordinates of the section along x, we have a thickness, so at xi we have ti.
Introduction to R & P
Blade section geometry
Resistance and Propulsion of Ships
t /2 Camber line
The camber line defines the line that passes through the middle of thickness of the section along xs
Introduction to R & P
Blade section geometry
Resistance and Propulsion of Ships
t /2 Camber line
If we know the camber distribution f (xs) and the thickness distribution t(xs), then we can determine the offsets to the section’s pressure and suction sides.
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