Sea conditions are critical to carrier flight
operations, replenishment operations, undersea warfare
operations, amphibious operations, and search and
rescue missions. Your observations of sea conditions
are vitally important. They must be accurate so that
forecaster and operations personnel may predict the
success of planned operations. The majority of waves
are disturbances on the surface of the water produced by
blowing winds. Although there is some net
displacement of water in waves, the majority of the
movement of water in a wave is in a circular motion
beneath the surface. Waves move across the surface of
the water by transferring energynot matter. Waves
move in a sine wave pattern, as shown in figure 1-31.
The success of any operation conducted in the
ocean environment may depend on the height of the
seas, the direction of the seas, and the wave period.
Waves, in general, are described by wave height, wave
length, and wave period. Wave direction is another
important aspect used to describe waves.
In oceanography, wave height (fig. l-31) is the
vertical distance, usually measured in feet, from the
crest of a wave (the highest portion of a wave) to the
trough of the wave (the lowest portion of the wave).
This differs from the "wave height" or "amplitude"
normally used in physics, in which the distance is
measured from the "at rest" or midline position to the
crests and troughs. When waves are generated by the
force of wind acting on the water, the wind speed
determines the maximum height of the wave. For a
given wind speed, many different wave lengths
(frequencies) are produced, and for each wave length
(frequency), many different wave heights are
developed. Although the general relationship that
higher waves tend to have longer wave lengths (lower
frequencies) is true, there is no specific relationship
between wave height and wave length.
The primary factor that determines the maximum
wave height is the wind speed. But the duration of the
wind (length of time the wind has been blowing at a
certain wind speed) and the fetch, (distance over the
water the winds have been blowing) also limit the
maximum wave height. When the highest theoretical
wave height based on the wind speed cannot be attained
because the winds have not blown for a sufficient period
of time, the sea heights are said to be duration limited.
When the sea heights cannot be attained because the
straight line area the winds have been blowing over the
water is too short, the sea heights are said to be fetch
limited. The tables in Appendix V provide a breakdown
of wind speeds in relation to wave heights and a wind
and sea scale for a fully arisen sea.
The table in Appendix V also refers to the 10 states-
of-the-sea, or sea-states. Although not used
extensively, sea-states may be mentioned in literature or
messages. Sea-states refers to general descriptions of
wave heights and the appearance of the water surface.
They range from "calm" and "sea like a mirror," as in
sea-state 0, to "exceptionally high waves" with the "air
filled with foam and spray" as in sea-state 9.
Accurate observations of wave height are the most
difficult determination in an observation, especially
from the catwalk on an aircraft carrier. Typically,
observers on large ships, such as an aircraft carrier,
significantly underestimate the wave height, while
observers on smaller ships and in small boats provide
Figure 1-31.Sine wave pattern and associated parameters in ocean waves.