Ship Motions (Six Degrees of Freedom)

Ship Motions describe the ways a vessel moves in response to the sea, classified as the six degrees of freedom: three rotational and three translational. The rotations are Roll (side-to-side tilt about the fore-and-aft axis), Pitch (bow rising and falling about the transverse axis), and Yaw (bow swinging left/right about the vertical axis). The translations are Heave (up and down), Sway (side to side) and Surge (fore and aft).

These motions, driven by waves, affect cargo securing, crew safety and comfort, cargo and machinery loads, and operations (rolling can shift or damage cargo; heavy pitching slams the bow; excessive roll risks stability). Understanding and predicting ship motions is central to stowage and lashing, stability, seakeeping design, and safe operations such as cargo work, offshore lifts and crew transfers. Roll in particular is managed with bilge keels, stabilisers and careful loading (metacentric height). Ship motions are a fundamental concept in seakeeping and safe ship operation, underlying why cargo must be secured and how vessels are designed to behave in a seaway.