ssc-367 - Ship Structure Committee

In many cases wind informationmay be available from transmitting
ships or nearby coastal weather stations for areas where wave data
is either skimpy or questionable. For these cases various equations
have been developed to estimate or verify the wave information.
Example equations to relate wind speed to wave height can be as
simple as the “25% Rule”,
H~ = 0.25 * U
where Hs is the significant wave height in feet and U is the
observed wind speed in feet/see. More involved equations include
the wind “fetch” and the wind duration. The wind fetch is the
distance over water that the wind acts. Appendix B presents the
equations developed by Bretschneider to calculate wave height and
period based on wind speed, duration and fetch.
Hindcast Data
Elaborate computer models have been developed to “hindcast” or
recreate weather (wind and wave) records. The hindcast models may
be for a region (such as the North Sea), or the models may be
oceanic or even global. One important consideration in the
developmentof hindcastmodels is the sensitivityof these modelsto
interaction of various parameters. Using available wind and wave
data to correlate the hindcast results can improve the accuracy of
hindcast models.
The hindcast models derive wind information from pressure and
temperatureinformation. Pressuremeasurementsare fairlyaccurate,
and the techniques of combining the pressure readings from many
measurementstationsto produceisobarplots allowsdeterminationof
the pressures over a large region without making measurements at
each grid point. The temperatures measured at coastal weather
stations surrounding the area of interest along with whatever
temperature measurements available from the area can be used to
identify temperature gradients, fronts, etc.
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