A vessel in a waterway experiences dynamic motions in six degrees of motion. Stresses can also induce hull deformation.
The transverse axis is measured across the beam of the ship (from port to starboard). A rotation about the transverse axis are known as pitch. Motions along the length of the transverse axis are known as sway.
The tendency to roll is referred to as the stiffness of a boat - boats may be considered stiff, or tender. There are a number of ways to control roll such that the roll period is comfortable for passengers, or to limit roll for operational requirements. Systems can be active or passive, and include skegs, bilge keels, stabilizing fins, and/or anti-heel heel systems and anti-roll tanks.
Sway is a particular concern for sailing vessels, which can use keels, leeboards, bilgeboards, daggerboards, or centreboards to reduce this effect, often attempting to convert lateral motion (sway) into forward thrust (by producing lift, i.e., the use of foil sections).
See main article, Yaw Yaw can be induced by control surfaces, such as rudders, by propulsors such as Voith Schneider drives or azimuthing propulsion, or by the environment. Alternatively, vessels can be designed to decrease susceptibility to yaw, such as skegs or larger L/B ratios.