Rudder: It is an equipment which is used to steer or control a ship, boat, submarine or any other means to maneuver on a fluid medium. Type of rudder is selected considering some factors. These factors include speed in which vessel is operating, propeller design, form of hull, structural arrangement of stern, distance between stern and propeller  etc.

Types of Rudder:

  • Balanced Rudder
  • Un-Balanced Rudder
  • Semi Balanced Rudder

1.Balanced Rudder

  • In this type of rudder, the rudder is attached to the rudder stock (axis of rudder)only at the top of the rudder .
  • Rudder stock is placed such as 40% of the rudder area is forward of the stock and remaining are aft of it. This helps in eliminating torque as 30% to 40% of rudder area is forward. Elimination of torque results in keeping the rudder at one angle without changing.
  • Centre of gravity of the rudder is at almost 40% of length from its forward. So if the rudder is placed near to this area the torque required to rotate the rudder will be less than what is actually required. So Balance rudder needs only little torque to rotate.
  • As balance rudder needs only a little torque to rotate, it reduces the energy consumption of steering gear equipment thereby reducing the fuel consumption of the ship.
  • It can be vulnerable to vertical displacement .
2.Un-Balanced Rudder

  • In the case of Un-Balanced rudder the rudder stock is attached at the forward most point of span of rudder.
  • Rudder stock runs along the entire length of the rudder, unlike balanced rudders.
  • Here the torque required to rotate the rudder is very large compared to a balanced rudder.
  • Because of this high torque rudder is fixed to the spintle to prevent vertical displacement from its natural position.
  • These type of rudders are not widely used now.
3. Semi- Balanced Rudder

  • It is clear that both balanced and un-balanced types of rudders have significant problems. That is a problem with the steering gear mechanism would create a lot of problem by rudder staying at the angle it was at(Angle of attack) instead of coming to midship.
  • To reduce this Semi balanced rudder was introduced.
  • This type of rudder is partly Balanced and partly Un-Balanced.
  • Semi -Balanced rudder is made in such a way that a portion from the top of length is unbalanced and the remaining part is balanced.
  • Due to the top part being unbalanced, the structural support increases and it helps in preventing vertical displacement.
  • The Balanced part of the rudder helps in reducing the torque and increasing fuel efficiency.
  • So , if anything occurs to steering gear mechanism the rudder won't stay at the angle of attack and it will return to midship.
Unconventional Rudder systems:

Apart from the Conventional rudder systems, there are unconventional systems including,
  • Pleuger Rudder
  • Flaps Rudder