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Rudder area is usually between 1/60th to 1/70th of the vessel’s Length X Draught.
Ratio of Depth to Width (aspect ratio) is 2:1.

3 TYPES OF RUDDER:

Unbalanced rudder: Whole rudder area aft of stock

Components:
– Sole piece is a forging to form lower gudgeon supporting bearing pintle, and connect to aftermost keel plate
– Sternpost is formed by solid round bar with heavy plates welded to it. Boss is positioned to suit height of shaft.
– Side shell plates are riveted or welded to the plates forming the sternframe. This forms the arch which joins sternpost to rudderpost.
– Centreline web is thick to ensure rigidity of the arch.
– Rudderpost consists of thick web plate fitted at after side, and 1 or more gudgeons fitted to support the rudder.
– The web plate is continued inside the ship at the top of the rudder post and attached to a thick transom floor which is watertight.

– The rudder is supported by pintles which fit into the gudgeons. Upper part of the pintle is tapered to fit into the rudder gudgeons. The pintle is pulled hard against the taper with a large nut with suitable locking device (e.g. split pin or lock nut). A brass liner is fitted round the lower part of the pintle.
– Modern polymer based bearing material is dovetailed into stern frame gudgeon to provide a bearing surface for the pintle, allowing it to turn but preventing any side movement.
– Locking pintle: A head is fitted to the upper pintle to prevent undue vertical movement of the rudder.
– Bearing pintle: The bottom pintle rests on a hardened steel pad shaped to suit the bottom of the pintle.

Balanced rudder: 20%~40% of rudder area forward of stock, and *no torque on the stock at some rudder angle*.

– Constructed of double plates, with a large tube down the centre.
– Rudder post is formed by a detachable forged steel main piece which is carried through the tube, bolted to a palm on the stern frame at the top and pulled against a taper in the lower gudgeon.
– Main piece is increased in diameter at the top and bottom where suitable bearing strips are fitted.
– Castings are fitted at the top and bottom of the tube to carry the bearing strips.
– Hard steel bearing rings are fitted between the rudder and the bottom gudgeon to take the weight of the rudder.
– Horizontal coupling attaches the stock to the rudder with the aid of fitted bolts.
* Must have sufficient vertical clearance between main piece and stock to clear the bottom gudgeon when removing the rudder.
– Upper stock is usually supported by a rudder carrier.
* By balancing a rudder, the stock’s diameter was reduced. This allows reduction in the thickness of the side plates and size of the steering gear.
– A flat bar is welded to the bottom of the horn to restrict the lift of the rudder.
– Clearance between rudder and flat bar < Cross-head clearance * So any vertical force on rudder will be transmitted to sternframe, not to steering gear

Spade rudder: Supported by means by a gudgeon on a large rudder horn and by the lower end of the stock, which is carried straight into the rudder and is either of a keyed/keyless design.

– Spade rudder is unsupported at the bottom and hence open aperture is possible.
– Lower part at aft end “Deadwood” is cut away, allows better flow of water to propeller.
* In addition, the distance of rudder from propeller may be adjusted to improve efficiency of rudder.

Semi-balanced rudder: Part of rudder area forward of stock but *not balanced at any rudder angle*.

– Rudder frame consists of a main piece with horizontal arms which are streamlined.
– Side plates are riveted or welded to frame.
* Must have sufficient vertical clearance between lower part of stern frame and extension of the rudder to allow rudder to be lifted clear of the bearing pintle.
– Main piece must be strong to prevent undue deflection of the lower, unsupported portion.

RUDDER REMOVAL AT DRYDOCK

RUDDER CARRIER

• This topic was modified 2 years, 2 months ago by Admin.
• This topic was modified 2 years, 2 months ago by Admin.

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