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Ship Rudder


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Ship's rudder, Rudder stock, rudder post, pintles and bearing, types of rudders etc.

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Ship Rudder

  1. 1. Ship Rudder 01/16/19 1
  2. 2. Rudder Rudders are a means of directional control of ship Rudders are fitted at aft end because… a. derive benefit of increased water velocity induced by the propeller – esp. at low speed b. to create the maximum distance from the ship’s neutral point where lateral force does not cause ship to deviate from a constant direction…’neutral point’ is forward of midship 01/16/19 2
  3. 3. Rudder Neutral point is the point in the length of the ship at which an applied force (lateral) DOES NOT cause the ship to deviate from a constant direction Generally, neutral point is forward of midship. Hence rudder is most effective when located aft, and it gives maximum turning effect. 01/16/19 3
  4. 4. Rudder Size and shape of rudder is governed by: a. shape and type of stern b. area of rudder deemed necessary c. capacity of steering gear d. service condition of ship Three types of rudder a. balanced b. unbalanced c. semi-balanced 01/16/19 4
  5. 5. Types of rudder The main purpose of balancing rudder is to achieve the reduction in the torque required of the steering gear. 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 01/16/19 5
  6. 6. 01/16/19 6 TYPES OF RUDDER
  7. 7. Balanced Rudder  Axle fitted at its turning axis with large area forward of the axis (25% to 30 %).  Upper and lower bearings are fitted in the rudder.  The bearing consists of a stainless steel bush in the rudder and a stainless steel liner on the axle.  The stainless steel bush is spirally grooved to permit lubrication.  Other materials are in use, such as gun metal for liner and lignum vitae or tufnol for the bush. 01/16/19 7
  9. 9. Unbalanced Rudder Full area aft of the axis.  Fitted with upper, mid and lower arms rested on gudgeons.  At the bearing pintle fitted with hard steel disc and locking nut.  The ordinary pintle arranged with bush and locking nut and the locking pintle at the top part of the rudder secured by locking nut.  Turn on pintles and have a small portion of their lateral area forward of the turning axis (less than 20%).  Commonly fitted on twin screw vessels where most of it hinged on a body post by pintles and gudgeons.01/16/19 9
  10. 10. Unbalanced Rudder 01/16/19 10
  12. 12. Semi-Balanced Rudder  Which are very common today. Have less than 20% of the lateral area forward of the axis.  Modern ship’s use this design of rudder. 01/16/19 12
  13. 13. Semi-balanced Rudder 01/16/19 13
  14. 14. Rudder Pintles Pintles on which the rudder turns in the gudgeons have a taper on the radius, and a bearing length which exceeds the diameter. Older ships may have a brass or bronze liner shrunk on the pintles which turn in lignum vitae (hardwood) bearings fitted in the gudgeons. Modern practice is to use synthetic materials like ‘Tufnol’ for the bearings, and in some cases stainless steels for the liners. In either case lubrication of the bearing is provided by the water in which it is immersed. 01/16/19 14
  15. 15.  Locking pintles are designed to prevent the rudder lifting.  Bearing pintles take part of the rudder’s weight Function of the Rudder Pintles 01/16/19 15
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  17. 17. Bearing Pintle 01/16/19 17
  18. 18. Locking Pintle 01/16/19 18
  19. 19. Ordinary Pintle 01/16/19 19
  20. 20. RUDDER BEARING:  The weight of the rudder may be carried partly by the lower pintle and partly by a rudder bearer within the hull.  In some rudder types, for example, the spade type which is only supported within the hull, the full weight is borne by the bearer.  A rudder bearer may incorporate the watertight gland fitted at the upper end of the rudder trunk.  Most of the rudder’s weight may come onto the bearer if excessive wear down of the lower pintle occurs, and the bearers illustrated have cast iron cones which limit their wear down. 01/16/19 20
  21. 21. Rudder angle normally does not exceed 35 degrees. Why?  avoid stalling of rudder  avoid flow separation on low pressure side  avoid reduction of effectiveness of control surface  avoid sudden discontinuity of lift force on downstream surface of rudder OR increase in drag force 01/16/19 21
  22. 22. Lift to Drag ratio of Rudder 01/16/19 22
  23. 23. • Effect on rudder stock of different rudder configuration  Balanced rudder….centre of pressure on turning axis at about 15 degrees, no torque on rudder stock  Unbalance rudder….centre of pressure is furthest from turning axis, high torque on rudder stock 01/16/19 23
  24. 24. Rudder Pintles and Carriers  A head is fitted to the upper pintle to prevent undue vertical movement of the rudder – locking pintle  The bottom pintle is known as a bearing pintle since it rests on a hardened steel pad  Bearing pintles are only required to support the weight of the rudder in the event of the rudder carrier failing  It is essential that the centreline of stock and pintles are in the same line, otherwise the rudder will not turn  Appreciable wear of bearing generally is due to the misalignment of the rudder stock  The major part of the rudder’s weight is carried by the rudder carrier 01/16/19 24
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  26. 26. Watertight Gland for Rudder Stock A separate watertight gland is often fitted where the stock enters the rudder trunk. A small opening with watertight cover may be provided in one side of the trunk, which allows access to a greater length of the rudder stock It also removes the need for a watertight construction of the carrier bearing and reduces the unsupported length of the stock 01/16/19 26
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  30. 30. Construction of Rudder Modern rudder is of double plate construction and the steel plate sides are welded to an internal webbed framework. Rudder framework can be of cast steel or fabricated of web plates welded together Integral with the internal framework may be heavy forging which form the gudgeons or bearing housing for the rudder The upper face of the rudder is formed into a usually horizontally/vertically flat palm of coupling for the stock A lifting hole is provided for lifting when fitting/removal Closing plate slot-welded to flat bars, which are welded to edge of internal frames. 01/16/19 30
  31. 31. Construction of Rudder Inside of the rudder is coated with bitumastic preservative or filled with inert foam Vent plugs are provided for venting and draining The rudder stock is connected to the rudder by vertical or horizontal coupling with fitted bolts and are locked by pins 01/16/19 31
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  33. 33. Advantages of a Double Plate Rudder Lighter , stronger Reduce appendages resistance because of its streamlined , smooth surface/shape Greater lift force produce due to aerofoil cross- section Buoyancy reduced carrier bearing and coupling load Perforation of one side due to corrosion/damage does not reduce its effective area. 01/16/19 33
  34. 34. Special Rudders In addition to the conventional types of rudder, there are some special types of rudder in use depending on the service condition of the ships. Spade Rudders Also known as ‘skeg rudder’, it is a free hanging fully balanced rudder in the shape of a spade. It has no external supports in the form of pintles and is entirely supported by its stock…purpose of this design? The stock is 30% heavier; shape tends to shift the C.P to turning axis and reduce B.M on stock; no pintles benefits 01/16/19 34
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  36. 36. Flettner/Becker Rudders Flap or flaps of small area are hinged to the trailing edge of the rudder These flaps are independently controlled and can improve steering capability when activated without increasing its drag force at large angle The flap having a high aspect ratio gives a high lift to drag ratio which improves steering capability. 01/16/19 36
  37. 37. Borg Rudders It is a rotary unit that provide maximum manoeuvrability while operating at low speeds abd while carrying heavy load It uses the magnus effect to steer the ship..a cylindrical body, rotating in a fluid develops a high lifting force at right angles to the flow on the side of the rotor turning in accord with the fluid flow. Lift force increases rapidly as the surface speed of the cylinder increases 01/16/19 37
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  39. 39. Pleuger Active Rudders It is an active rudder that does not depend on the speed of the ship to be effective It has a streamlined body mounted on it that houses an electric motor coupled to a ducted propeller This arrangement can actually turn the ship around its own length even when she is at rest 01/16/19 39
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