How does a rudder help steer a boat?

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Alaska: Commercial fishing — boat A commercial salmon-fishing boat in Alaska.

A rudder is a steering component typically attached to the stern of a boat. It functions based on the principle of unequal water pressure.1

When you turn the rudder, one side becomes more exposed to the flow of water than the other. This creates a pressure difference that thrusts the stern away from the side the rudder is turned toward, causing the boat to swerve from its original course. In small watercraft, this mechanism is controlled manually using a tiller or helm.1