What are square waves and how are they dangerous for ships?

When colliding oncoming waves at an angle of 90 degrees, so-called rectangular waves can sometimes form. Such a spectacle can amaze observers, because the water looks like a chessboard.

The place Ile-de-Re (France), in which square waves appear often, has become a tourist attraction thanks to this phenomenon. Visitors climb the lighthouse to get a better look at such waves.

As a rule, the phenomenon occurs under the condition that the wind pushes the waves in one direction, and the current in another. This often happens with tropical storms. In shallow water areas, rectangular waves do not pose a particular danger to people, but away from the shore, such waves can seriously rock the ship.

One of the recent studies showed that a disproportionately large number of accidents on the water were recorded precisely in the waters subject to the occurrence of rectangular waves.