What is it called when the bow of a fast-moving boat bobs up and down in calm water?

The phenomenon of the bow of a fast-moving boat bobbing up and down in calm water is known as porpoising. This occurs when the boat's speed causes it to lift out of the water and then fall back, creating a rhythmic motion similar to that of a porpoise surfacing and diving. This motion can be influenced by the boat's design, weight distribution, and speed.

Porpoising can affect the handling and stability of the vessel, making it important for operators to recognize and understand this behavior for safe navigation. By adjusting the boat’s speed and trim, operators can often minimize this motion, ensuring a smoother ride.