Roll is a motion of a vessel about it's longitudinal axis (a change in heel). Principally for reasons of resistance, sea-keeping and buildability, vessels tend to be longer than they are wide. The lower transverse waterplane moment of inertia which results means a vessels roll will be more pronounced that its pitch or yaw. Roll is thus the most noticeable of ship motions in general experience. A number of appendages and devices have been designed to dampen roll to increase comfort for passenger and crew (as well as to lower accelerations on equipment and mountings).