What is the primary function of a tiller on a boat?

The primary function of a tiller on a boat is to turn the rudder for steering. When a person pushes or pulls the tiller, it pivots the rudder in the water. This action changes the direction of the boat, allowing the operator to maneuver effectively while navigating. A tiller is a simple and effective steering device commonly found on smaller boats, particularly those without a wheel, thus providing direct control over the boat's heading.

The other options represent different aspects of boating activities but do not relate to the specific function of a tiller. The provision of power to the engine is typically managed by the engine and its components, while securing the boat to the dock involves lines or anchors rather than the tiller. Setting the boat's sail angle pertains to the operation of sails in sailing vessels, which is a separate function from steering.