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Propellers, Rudders and Bow
          Thrusters
         Burak Acar
Ship Drive Train and Power

Ship Drive Train System
                                             EHP


  Engine     Reduction
               Gear                        Strut Screw
                         Bearing   Seals


                                                     THP

           BHP   SHP                          DHP
EHP


Engine
                                                 Strut
                   Reduction                                   Screw
                     Gear      Bearing   Seals




                                                               THP

                                                         DHP
            BHP
                       SHP




  Brake Horsepower (BHP)
     - Power output at the shaft coming out of the engine
  before
         the reduction gears
EHP


Engine
                                             Strut
               Reduction                                   Screw
                           Bearing
                 Gear                Seals




                                                           THP

         BHP                                         DHP
                   SHP




Shaft Horsepower (SHP)
- Power output at the shaft coming out of the reduction gears
EHP


Engine
                                                  Strut
                    Reduction                                     Screw
                      Gear      Bearing   Seals




                                                                  THP

              BHP
                                                            DHP
                        SHP




     Delivered Horsepower (DHP)
         - Power delivered to the propeller
         - DHP=SHP – losses in shafting, shaft bearings and seals
EHP


Engine
                                                Strut
                  Reduction                                         Screw
                    Gear      Bearing   Seals




                                                                    THP
            BHP                                               DHP
                      SHP




 Thrust Horsepower (THP)
     - Power created by the screw/propeller
     - THP=DHP – Propeller losses
     - THP is the end result of all HP losses along the drive train
PROPELLER
Types of Propellers
• Fotokopiler
The Screw Propeller
7.9 Screw Propeller




               Diameter
               Hub
               Blade Tip
               Blade Root
Pitch Distance   Variable Pitch
Pitch Angle      Controllable Pitch
Fixed Pitch      (Constant Speed)
Basic Nomenclature:
•   Hub The hub of a propeller is the solid center disk that mates with the propeller shaft and to
    which the blades are attached. Ideally the hub should be as small in diameter as possible to
    obtain maximum thrust, however there is a tradeoff between size and strength. Too small a hub
    ultimately will not be strong enough.

•   Blades Twisted fins or foils that protrude from the propeller hub. The shape of the blades and the
    speed at which they are driven dictates the torque a given propeller can deliver.

•   Diameter The diameter (or radius) is a crucial geometric parameter in determining the
•   amount of power that a propeller can absorb and deliver, and thus dictating the amount of
•   thrust available for propulsion. With the exception of high speed (35 Knots+) vehicles
•   the diameter is proportional to propeller efficiency (ie. Higher diameter equates to higher
•   efficiency). In high speed vessels, however, larger diameter equates to high drag. For
•   typical vessels a small increase in diameter translates into a dramatic increase in thrust
•   and torque load on the engine shaft, thus the larger the diameter the slower the propeller
•   will turn, limited by structural loading and engine rating.
Basic Nomenclature:
• Revolutions per Minute (RPMs) RPM is the number of full turns or
  rotations of a propeller in one minute. RPM is often designated by
  the variable N. High values of RPM are typically not efficient except
  on high speed vessels. For vessels operating under 35Knots speed,
  it is usual practice to reduce RPM, and increase diameter, to obtain
  higher torque from a reasonably sized power plant. Achieving low
  RPM from a typical engine usually requires a reduction gearbox.

• Pitch The pitch of a propeller is defined similarly to that of a wood or
  machine screw. It indicates the distance the propeller would “drive
  forward” for each full rotation. If a propeller moves forward 10inches
  for every complete turn it has a 10inch nominal pitch. In reality since
  the propeller is attached to a shaft it will not actually move forward,
  but instead propel the ship forward. The distance the ship is
  propelled forward in one propeller rotation is actually less than the
  pitch. The difference between the nominal pitch and the actual
  distance traveled by the vessel in one rotation is called slip.
Screw Propeller

• Variable Pitch (the standard prop):
 - The pitch varies at the radial distance from the hub.
 - Improves the propeller efficiency.
 - Blade may be designed to be adjusted to a different
   pitch setting when propeller is stopped.

• Controllable Pitch :
  - The position of the blades relative to the hub can be
    changed while the propeller is rotating.
  - This will improve the control and ship handling.
  - Expensive and difficult to design and build
Right and Left Hand Props




     Left Hand   Right Hand
Suction Face


                               Leading Edge


Trailing Edge
                    Pressure Face
Propeller Walk
• Due to a difference in the pressure at
  the top and bottom of the prop (due to
  boundary layer), the lower part of the
  prop works harder.
• This leads to a slight turning moment.
• Right hand props cause turns to port
  when moving ahead.
Prop Walk Solutions
• Twin Screws
• Counter rotating propellers (one shaft)
• Tunnels/shrouds (nozzle)
Shrouded (nozzle) prop
Skewed Screw Propeller
   Highly Skewed Propeller
                              Advantages
                             - Reduce interaction between
                               propeller and rudder wake.
                             - Reduce vibration and noise



                              Disadvantages
                             - Expensive
                             - Less efficient operating in
                               reverse



DDG51
Propeller Theory
Propeller Theory
 • Speed of Advance           Vwater= 0
                      P
                                                   Wake Region
                             VS                  VW
                      Q
                              Vwater= VS
  • The ship drags the surrounding water so that the wake to
    follow the ship with a wake speed (Vw) is generated in the
    stern.
  • The flow speed at the propeller is,

           VA = VS − VW                     Speed of Advance
Propeller Cavitation

• Cavitation : Definition

 - The formation and subsequent collapse of vapor bubbles
   on propeller blades where pressure has fallen below the
   vapor pressure of water.


 - Bernoulli’s Equation can be used to predict pressure.


 - Cavitation occurs on propellers (or rudders) that are
 heavily loaded, or are experiencing a high thrust loading
 coefficient.
1 atm=101kpa
     =14.7psi
Blade Tip Cavitation     Navy Model Propeller 5236

                                Flow velocities at the
                                tip are fastest so that
                                pressure drop occurs at
                                the tip first.

                                  Sheet Cavitation




Large and stable region
of cavitation covering the
suction face of propeller.
Propeller Cavitation
Consequences of Cavitation

 1) Low propeller efficiency (Thrust reduction)
 2) Propeller erosion (mechanical erosion as bubbles
 collapse, up to 180 ton/in² pressure)
 3) Vibration due to uneven loading
 4) Cavitation noise due to impulsion by the bubble
 collapse
Propeller Cavitation
• Preventing Cavitation
 - Remove fouling, nicks and scratch.
 - Increase or decrease the engine RPM smoothly to avoid
  an abrupt change in thrust.
     rapid change of rpm ⇒ high propeller thrust but small
     change in VA ⇒ larger CT ⇒ cavitation &
     low propeller efficiency
 - Keep appropriate pitch setting for controllable pitch
 propeller
 - For submarines, diving to deeper depths will delay or
 prevent cavitation as hydrostatic pressure increases.
Propeller Cavitation
• Ventilation

  - If a propeller or rudder operates too close to the water
  surface, surface air or exhaust gases are drawn into the
  propeller blade due to the localized low pressure around
  propeller. The prop “digs a hole” in the water.
  - The load on the propeller is reduced by the mixing of
  air or exhaust gases into the water causing effects
  similar to those for cavitation.
  -Ventilation often occurs in ships in a very light
  condition(small draft), in rough seas, or during hard
  turns.
Other forms of propulsion




A one horsepower cable-drawn ferry!
RUDDER
Ship rudder
• rudder is the most important ship control
   surface
• a fin-like projection under the counter and
   below the waterline – placed as far aft as
   practical
• mounted onto a circular shaft referred to
   as the stock – penetrates the hull through
   bearings
Ship rudder – basic definitions
Ship rudder – forces on a foil
Area and shape of rudders
• no fixed rule for determination of the size

• in practice, rudder area, expressed as a
   fraction of the product of the length and
   draft or centerline plane area, often
   selected by comparison with a ship with
   similar maneuverability requirements
• (Rudder Area)Cargo Ships = 0.017 * LOA * T
Area and shape of rudders -
          types
Area and shape of rudders -
                types
• rudder consists of two parts: the blade (flat part) against which the
    water pressure acts and the stock (shaft) which transmits motion of
    the steering gear to the blade

• there are 3 types of rudders:

balanced: a portion of the blade area is disposed symmetrically through
   the rudder height and fwd of stock

unbalanced: blade is entirely aft of stock

semi-balanced: area fwd of stock does not extend to the full height of
  the blade aft of the stock – upper portion may be considered
  unbalanced and the lower portion, balanced
Area and shape of rudders
                   Modern double-plate,
                   semi-balanced rudder
                   in a single screw ship
BOW THRUSTERS
Rotatable Thrusters and
      Propellers
Actuator Models
Actuator Models
Propeller and Rudder

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Propeller and Rudder

  • 1. Propellers, Rudders and Bow Thrusters Burak Acar
  • 2. Ship Drive Train and Power Ship Drive Train System EHP Engine Reduction Gear Strut Screw Bearing Seals THP BHP SHP DHP
  • 3. EHP Engine Strut Reduction Screw Gear Bearing Seals THP DHP BHP SHP Brake Horsepower (BHP) - Power output at the shaft coming out of the engine before the reduction gears
  • 4. EHP Engine Strut Reduction Screw Bearing Gear Seals THP BHP DHP SHP Shaft Horsepower (SHP) - Power output at the shaft coming out of the reduction gears
  • 5. EHP Engine Strut Reduction Screw Gear Bearing Seals THP BHP DHP SHP Delivered Horsepower (DHP) - Power delivered to the propeller - DHP=SHP – losses in shafting, shaft bearings and seals
  • 6. EHP Engine Strut Reduction Screw Gear Bearing Seals THP BHP DHP SHP Thrust Horsepower (THP) - Power created by the screw/propeller - THP=DHP – Propeller losses - THP is the end result of all HP losses along the drive train
  • 10. 7.9 Screw Propeller Diameter Hub Blade Tip Blade Root
  • 11. Pitch Distance Variable Pitch Pitch Angle Controllable Pitch Fixed Pitch (Constant Speed)
  • 12. Basic Nomenclature: • Hub The hub of a propeller is the solid center disk that mates with the propeller shaft and to which the blades are attached. Ideally the hub should be as small in diameter as possible to obtain maximum thrust, however there is a tradeoff between size and strength. Too small a hub ultimately will not be strong enough. • Blades Twisted fins or foils that protrude from the propeller hub. The shape of the blades and the speed at which they are driven dictates the torque a given propeller can deliver. • Diameter The diameter (or radius) is a crucial geometric parameter in determining the • amount of power that a propeller can absorb and deliver, and thus dictating the amount of • thrust available for propulsion. With the exception of high speed (35 Knots+) vehicles • the diameter is proportional to propeller efficiency (ie. Higher diameter equates to higher • efficiency). In high speed vessels, however, larger diameter equates to high drag. For • typical vessels a small increase in diameter translates into a dramatic increase in thrust • and torque load on the engine shaft, thus the larger the diameter the slower the propeller • will turn, limited by structural loading and engine rating.
  • 13. Basic Nomenclature: • Revolutions per Minute (RPMs) RPM is the number of full turns or rotations of a propeller in one minute. RPM is often designated by the variable N. High values of RPM are typically not efficient except on high speed vessels. For vessels operating under 35Knots speed, it is usual practice to reduce RPM, and increase diameter, to obtain higher torque from a reasonably sized power plant. Achieving low RPM from a typical engine usually requires a reduction gearbox. • Pitch The pitch of a propeller is defined similarly to that of a wood or machine screw. It indicates the distance the propeller would “drive forward” for each full rotation. If a propeller moves forward 10inches for every complete turn it has a 10inch nominal pitch. In reality since the propeller is attached to a shaft it will not actually move forward, but instead propel the ship forward. The distance the ship is propelled forward in one propeller rotation is actually less than the pitch. The difference between the nominal pitch and the actual distance traveled by the vessel in one rotation is called slip.
  • 14. Screw Propeller • Variable Pitch (the standard prop): - The pitch varies at the radial distance from the hub. - Improves the propeller efficiency. - Blade may be designed to be adjusted to a different pitch setting when propeller is stopped. • Controllable Pitch : - The position of the blades relative to the hub can be changed while the propeller is rotating. - This will improve the control and ship handling. - Expensive and difficult to design and build
  • 15. Right and Left Hand Props Left Hand Right Hand
  • 16. Suction Face Leading Edge Trailing Edge Pressure Face
  • 17. Propeller Walk • Due to a difference in the pressure at the top and bottom of the prop (due to boundary layer), the lower part of the prop works harder. • This leads to a slight turning moment. • Right hand props cause turns to port when moving ahead.
  • 18. Prop Walk Solutions • Twin Screws • Counter rotating propellers (one shaft) • Tunnels/shrouds (nozzle)
  • 20. Skewed Screw Propeller Highly Skewed Propeller Advantages - Reduce interaction between propeller and rudder wake. - Reduce vibration and noise Disadvantages - Expensive - Less efficient operating in reverse DDG51
  • 21. Propeller Theory Propeller Theory • Speed of Advance Vwater= 0 P Wake Region VS VW Q Vwater= VS • The ship drags the surrounding water so that the wake to follow the ship with a wake speed (Vw) is generated in the stern. • The flow speed at the propeller is, VA = VS − VW Speed of Advance
  • 22. Propeller Cavitation • Cavitation : Definition - The formation and subsequent collapse of vapor bubbles on propeller blades where pressure has fallen below the vapor pressure of water. - Bernoulli’s Equation can be used to predict pressure. - Cavitation occurs on propellers (or rudders) that are heavily loaded, or are experiencing a high thrust loading coefficient.
  • 23. 1 atm=101kpa =14.7psi
  • 24.
  • 25. Blade Tip Cavitation Navy Model Propeller 5236 Flow velocities at the tip are fastest so that pressure drop occurs at the tip first. Sheet Cavitation Large and stable region of cavitation covering the suction face of propeller.
  • 26. Propeller Cavitation Consequences of Cavitation 1) Low propeller efficiency (Thrust reduction) 2) Propeller erosion (mechanical erosion as bubbles collapse, up to 180 ton/in² pressure) 3) Vibration due to uneven loading 4) Cavitation noise due to impulsion by the bubble collapse
  • 27. Propeller Cavitation • Preventing Cavitation - Remove fouling, nicks and scratch. - Increase or decrease the engine RPM smoothly to avoid an abrupt change in thrust. rapid change of rpm ⇒ high propeller thrust but small change in VA ⇒ larger CT ⇒ cavitation & low propeller efficiency - Keep appropriate pitch setting for controllable pitch propeller - For submarines, diving to deeper depths will delay or prevent cavitation as hydrostatic pressure increases.
  • 28. Propeller Cavitation • Ventilation - If a propeller or rudder operates too close to the water surface, surface air or exhaust gases are drawn into the propeller blade due to the localized low pressure around propeller. The prop “digs a hole” in the water. - The load on the propeller is reduced by the mixing of air or exhaust gases into the water causing effects similar to those for cavitation. -Ventilation often occurs in ships in a very light condition(small draft), in rough seas, or during hard turns.
  • 29. Other forms of propulsion A one horsepower cable-drawn ferry!
  • 31. Ship rudder • rudder is the most important ship control surface • a fin-like projection under the counter and below the waterline – placed as far aft as practical • mounted onto a circular shaft referred to as the stock – penetrates the hull through bearings
  • 32. Ship rudder – basic definitions
  • 33. Ship rudder – forces on a foil
  • 34. Area and shape of rudders • no fixed rule for determination of the size • in practice, rudder area, expressed as a fraction of the product of the length and draft or centerline plane area, often selected by comparison with a ship with similar maneuverability requirements • (Rudder Area)Cargo Ships = 0.017 * LOA * T
  • 35. Area and shape of rudders - types
  • 36. Area and shape of rudders - types • rudder consists of two parts: the blade (flat part) against which the water pressure acts and the stock (shaft) which transmits motion of the steering gear to the blade • there are 3 types of rudders: balanced: a portion of the blade area is disposed symmetrically through the rudder height and fwd of stock unbalanced: blade is entirely aft of stock semi-balanced: area fwd of stock does not extend to the full height of the blade aft of the stock – upper portion may be considered unbalanced and the lower portion, balanced
  • 37. Area and shape of rudders Modern double-plate, semi-balanced rudder in a single screw ship