'Freak' ocean waves hit without warning, new research shows

[knocker]

Having spent a fair bit of my life on top of a wave this is a subject that has always interested me. I have never actually experienced a rogue wave thank god but have witnessed significantly bigger waves embedded amongst much lower ones. You suddenly get a 70-80 foot wave when the norm is 50-60. A wall of water just about covers  it. Anyway I'm off to get the violin out.

Quote

Mariners have long spoken of 'walls of water' appearing from nowhere in the open seas. But oceanographers have generally disregarded such stories and suggested that rogue waves - enormous surface waves that have attained a near-mythical status over the centuries - build up gradually and have relatively narrow crests.

New research from the University of Oxford in collaboration with the University of Western Australia, however, shows that the anecdotal evidence may not be so far from the truth. Rather than coming at the end of a series of increasingly large waves, rogue (or freak) waves emerge suddenly, being preceded by much smaller waves.

Read more at: http://phys.org/news/2015-12-freak-ocean.html#jCp

The paper

Nonlinear dynamics of wave-groups in random seas: unexpected walls of water in the open ocean

Quote

This paper investigates the size and structure of large waves on the open ocean. We investigate how nonlinear physics modifies waves relative to those predicted by a linear model. We run linear random simulations and extract extreme waves and the surrounding sea-state. For each extreme event, we propagate the waves back in time under linear evolution before propagating the wave-field forward using a nonlinear model. The differences between large linear and nonlinear wave-groups are then examined. The general trends are that under nonlinear evolution, relative to linear evolution, there is, on average, little or no extra amplitude in the nonlinear simulations; that there is an increase in the width of the crest of the wave-group and a contraction of large wave-groups in the mean wave direction; that large waves tend to move to the front of a wave-packet meaning that the locally largest wave is relatively bigger than the wave preceding it; and that nonlinearity can increase the duration of extreme wave events. In all these trends, there is considerable scatter, although the effects observed are clear. Our simulations show that nonlinearity does play an important part in the formation of extreme waves on deep water.

http://rspa.royalsocietypublishing.org/content/471/2184/20150660

[Mokidugway]

Had to factor high amplitude waves into boat design ,afterall anything can happen out there and frequently does !!