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
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.
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
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
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
Other materials are in use, such as gun metal for liner
and lignum vitae or tufnol for the bush.
Full area aft of the axis.
Fitted with upper, mid and lower arms rested on
At the bearing pintle fitted with hard steel disc and
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
Commonly fitted on twin screw vessels where most
of it hinged on a body post by pintles and
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
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.
Locking pintles are designed to prevent the
Bearing pintles take part of the rudder’s
Function of the Rudder Pintles
The weight of the rudder may be carried partly by
the lower pintle and partly by a rudder bearer within
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.
Rudder angle normally does not exceed 35 degrees.
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
• Effect on rudder stock of different rudder
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
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
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
It also removes the need for a watertight construction of the
carrier bearing and reduces the unsupported length of the stock
Construction of Rudder
Modern rudder is of double plate construction and the
steel plate sides are welded to an internal webbed
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 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.
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
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-
Buoyancy reduced carrier bearing and coupling load
Perforation of one side due to corrosion/damage
does not reduce its effective area.
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.
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
The stock is 30% heavier; shape tends to shift the
C.P to turning axis and reduce B.M on stock; no
Flap or flaps of small area are hinged to the trailing edge of the
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.
It is a rotary unit that provide maximum manoeuvrability
while operating at low speeds abd while carrying heavy
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
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