The steering oar or steering board is an oversized oar

Oar

An oar is an implement used for water-borne propulsion. Oars have a flat blade at one end. Oarsmen grasp the oar at the other end. The difference between oars and paddles are that paddles are held by the paddler, and are not connected with the vessel. Oars generally are connected to the vessel by...

 or board

Lumber

Lumber or timber is wood in any of its stages from felling through readiness for use as structural material for construction, or wood pulp for paper production....

 to control the direction of a ship

Ship

Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

 or other watercraft

Watercraft

A watercraft is a vessel or craft designed to move across or through water. The name is derived from the term "craft" which was used to describe all types of water going vessels...

 prior to the invention of the rudder

Rudder

A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a 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...

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It is normally attached to the starboard side in larger vessels, though in smaller ones it is rarely, if ever, attached. The steering oar was crucial in the invention of larger vessels in a time when the technology for rudders did not exist. Steering oars were the typical steering mechanism on larger Viking ship

Viking ship

Viking ships were vessels used during the Viking Age in Northern Europe. Scandinavian tradition of shipbuilding during the Viking Age was characterized by slender and flexible boats, with symmetrical ends with true keel. They were clinker built, which is the overlapping of planks riveted together...

s.