well waves travel beyond the wind, either leaving the area where
it is blowing or continuing on after the wind has ceased. They are
usually low and long -- with low wave heights and long wave lengths --
and follow each other at approximately the same distance. Such waves
begin when sea waves "decay," their crests becoming lower and more
rounded and symmetrical until they proceed as an orderly series of
similarly sized waves. In outline, swells are shape much like a true sine
curve, the classic wave of laboratory theory. It's an efficient shape: As
long as they remain in deep water, swells can cross thousands of miles
of ocean and lose very little energy. They are among the longest of all
waves, not uncommonly measuring 1,000 feet from crest to crest and,
on rare occasions, measuring as much as a mile. They are also faster
than other waves. In the deep water of the open ocean they travel at 15
to 20 miles per hour, which allows them to pass through slower sea
waves and organize themselves into clusters called trains. Such
clusters eventually crash to shore as a succession of large breakers,
perhaps contributing to the myth of the "ninth wave." Many people
have believed that the ninth wave (or 10th or 3rd, depending on the
place) is always the largest. An hour of observation on any beach
should be enough to disprove the myth, though it lives on. Some waves
are larger than others, true, but the disparity is caused because swells
and sea waves sometimes pass into one another, combining their
energy and producing random waves much larger than average.
The steepness of a wave never exceeds a 1:7 ratio of height to length.
