Steerage way is the minimum speed a boat or ship must be moving through the water for its rudder to effectively control its direction. When a vessel has steerageway, it is controllable, while below this speed (or at rest), it is unmanageable by the helm.

Key Aspects of Steerage Way:
Controllability: It is the threshold where the water flow over the rudder allows it to steer the vessel.

Bare Steerageway: This term refers specifically to the slowest possible speed at which the vessel can maintain a straight course.

Context Dependent: The necessary speed for steerage depends on the vessel and conditions; for instance, more speed is required in heavy seas or high winds compared to calm water.

"In Irons": A sailboat lacking steerage while pointing directly into the wind is considered to be "in irons" or lacking headway, losing all ability to turn.

If a boat is moving due to a current but not moving through the water, it lacks steerageway.