The development of the rudder was one of the most important sea navigational inventions that have ever been invented. Before the twelfth century in northern Europe, ships were steered by a quarter-rudder mounted on the stern side of the vessel. Up until the fourteenth century the use of the quarter rudder persisted in the Mediterranean. Two quarter-mounted steering oars were used. By age of exploration, the pintle-and-gudgeon rudder, hung from the sternpost had replaced quarter-rudder.
The rudder brought great changes to the world. The voyages of Christopher Columbus may have never occurred if the Chinese had not of invented the rudder in first century AD.
The action of a rudder is basically very simple, The passage of the ship through the water causes water to flow past the rudder, and the angle at which the rudder is inclined to the direction of the flow is called the angle of attack. The steering action is dependent on the pressure distribution between the two hydrodynamic surfaces of the rudder. The pressure on the downstream side is less than the static pressure of the surrounding water while the pressure on the upstream side is greater. The result of this is an out ward force on the downstream side of the rudder, and this can be regarded as being made up of a list force at right angles to the direction of flow, and a drag force directly opposing the direction of flow.
The variation of the lift and drag forces for different angles of attack is extremely important in rudder design as it is the lift forces which creates the turning effect. At a certain angle of attack, called the critical angle, the rudder stalls: a phenomenon called burbling occurs and the rudder force is suddenly reduced. Burbling is caused by a breakdown in the streamlined flow, on the downstream side of the rudder there is a swirling irregular eddying flow. Rudders on merchant vessels are normally expected to operate up to an angle of 35 degrees from the centerline to port or starboard.
When a ships rudder is turned the ship first moves a small distance sideways in the opposite direction to the turn that was intended then moves around a circular path until it eventually faces the opposite direction. The distance moved forward from the point at which the ship is at right angles to its original direction is called advance.
Transfer is the sideways distance between these two points, and the diameter of the circular path followed by the ship is called the tactical diameter. During the turn the bow of the vessel lies always inside the turning curve, so that a drift angle is formed between the centerline of the vessel and the tangent to the turning curve. The tactical diameter is a measure of the ability of the rudder to turn the vessel. It is important for warships, because they frequently execute complicated turning maneuvers.
With a simple rudder arranged to turn around the edge nearest the ship, the force produced by the rudder will act to return the rudder to the straight-ahead position. To avoid excessive steering forces a balanced rudder arrangement is employed with the turning axis being positioned some way along the rudder near to the center of pressure of the center of pressure of the turning forces.
The earliest rudder in China was a balanced rudder. This means that part of the blade projected in front of the post. These rudders were easier to use, but Europeans did not adopt them until the nineteenth century. One of the earliest ships to use such a rudder was the Great Britain of 1843. The British were in the forefront when it came to adopting Chinese inventions for naval use, with this as well as the square-pallet chain pump as a bilge pump and water tight compartments in hulls. It is no exaggeration to say that the superiority of the British Navy was to a large extent due to its readiness to adopt Chinese invention more rapidly than other European powers.
Chinese seagoing rudders grew to many times the size of a man. Huge ships with enormous rudders were used on the Chinese voyages of discovery, which .