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How do yaw, sway, roll, pitch, heave, and surge describe a ship’s motions?

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naval architecture A cargo ship passing the Golden Gate Bridge, near San Francisco.

In naval architecture, a ship is treated as a rigid body that can experience six distinct oscillatory motions when navigating a seaway. These motions are categorized into three translatory (linear) movements and three rotary (angular) movements:12

Translatory Motions
* Surge: The oscillation of the ship in the fore-and-aft direction.12
* Sway: The side-to-side motion of the ship.12
* Heave: The vertical, up-and-down motion of the ship.12

Rotary Motions
* Roll: The angular rotation from side to side about a longitudinal (fore-and-aft) axis.12
* Pitch: The bow-up and bow-down motion about a transverse (athwartships) axis.12
* Yaw: The rotation or swing of the ship about a vertical axis.12

While these motions can occur simultaneously in a confused sea, they are often analyzed individually or in coupled systems to understand ship stability and performance. Managing these motions—particularly roll, which is a primary cause of seasickness—is a critical aspect of ship design, often involving the use of bilge keels or antiroll fins to dampen unwanted oscillations.12