Rudders

 A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other conveyance that moves through a fluid medium. On an aircraft, the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane.

    More on Wikipedia.

Construction of Rudders:-

    The Cellular framework form which rudders are constructed are usually of two types:    

1. Cast Type:-  These are cast in a foundry, brought to the shipyard, and enclosed in skin plating.
2. Prefabricated:- These are made in the yard itself, using horizontal and vertical plate webs welded together. These are more popular on modern ships.

Rudder Design:-

    The shape of a rudder plays an important role in its efficiency. Much technology goes into rudder design because and efficient rudder will mean : 

1. High maneuverability for the vessel. 
2. Faster turning responses.
3. Saving in fuel - less reduction in speed while turning etc.
4. Reduced stresses in the stern area.
5. Smaller steering gear required.

Types of Rudders:-

    There are three main types of rudders namely:-

1. Unbalanced Rudders - These are rudders having their entire turning area abaft the turning axis. They are relatively inefficient and today is only found on small ships, tugs, launches, and lifeboats.
2. Semi-balanced Rudders:- Those rudders which have a small proportion of their lateral area forward of the turning axis (usually less than 20%) and are found on larger vessels where due to constructional restraints, a balanced rudder could not be fitted for example twin-screw ships.
3. Balanced Rudders:- Rudders having their turning axis positioned so as to have as nearly as possible equal areas forward and aft. This is the most popular type of rudder found on modern ships. A typically balanced rudder would have about 20%-30% of the length forward of the turning axis.

In recent times, there have been several other hi-tech rudders that are being marketed. These are very efficient and would easily be fitted on ships having to maneuver often in restricted waters, and those using tugs for berthing, etc. Ferries and coastal tankers, RO ROs, and other ships are being fitted with these rudders.

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