Long crestedIf all the constituting waves of an open ocean travel in the same direction, they are called long crested wavesInfinitely long crests remain straight and parallel Long crested waves are never experienced outside the confines of the towing tank (sometimes, approximations may be found at sea)

Short crested wavesThe presence of more than one long crested wave system results in alternate enhancement and cancellation of wave crests and troughsThis phenomenon gives rise to a wave system with a spread of wave directions and is called a short crested seaway

Wave directionalityThe analysis and prediction of wave properties at a particular point on the ocean surface needs to take account of the directionality of the wave components

The concept of superposition of regular wave trains can be extended to include directionality

A wave energy spectrum derived from a record of surface elevations obtained at point in ocean will contain contributions from several different wave directions.

It is convenient to ignore this fact and assume that the wave system is long crested. For many purposes, this may give acceptable results.

The degree of wave spreading has a profound influence on some ship motions (particularly roll).Therefore, it cannot be ignored