The area of the Central North Sea is notorious for the occurrence of very high waves in certain wave trains. The short-term distribution of these wave trains includes waves which are far steeper than predicted by the Rayleigh distribution. Such waves are often termed “extreme waves” or “freak waves.” An analysis of the extreme statistical properties of these waves has been made. The analysis is based on more than 12 yr of wave records from the Mærsk Olie og Gas AS operated Gorm Field which is located in the Danish sector of the Central North Sea. From the wave recordings more than 400 freak wave candidates were found. The ratio between the extreme crest height and the significant wave height (20-min value) has been found to be about 1.8, and the ratio between extreme crest height and extreme wave height has been found to be 0.69. The latter ratio is clearly outside the range of Gaussian waves, and it is higher than the maximum value for steep nonlinear long-crested waves, thus indicating that freak waves are not of a permanent form, and probably of short-crested nature. The extreme statistical distribution is represented by a Weibull distribution with an upper bound, where the upper bound is the value for a depth-limited breaking wave. Based on the measured data, a procedure for determining the freak wave crest height with a given return period is proposed. A sensitivity analysis of the extreme value of the crest height is also made.

Danish Hydraulic Institute and LICenginecring AS, 1991, “Design Freak Waves,” Report for Mærsk Olie og Gas AS and The Danish Statoil Group (proprietary report).
Fenton, J. D., 1990, “Non-linear Wave Theories,” The Sea, Vol. 9, Part A, Ocean Engineering Science, Le Mehaute and Hanes, eds., John Wiley, New York, NY, Chap. 1, pp. 3–25.
S. F.
, “
Dangerous Wave Groups
Norwegian Maritime Research
, Vol.
, No.
, pp.
Klinting, P., and Sand, S. E., 1987, “Analysis of Prototype Freak Waves,” Proceedings ASCE Special Conference on Nearshore Hydrodynamics, University of Delaware, Newark, DE.
LICengineefing AS and Danish Hydraulic Institute, 1989, “Wave Kinematics. Extreme Waves,” Report for The Danish Statoil Group and Mærsk Olie og Gas AS (proprietary report).
Sand, S. E., Ottesen Hansen, N.-E., Klinting, P., Gudmestad, O. T., and Sterndorff, M. J., 1989, “Freak Wave Kinematics,” Proceedings, NATO ARW Workshop on Water Wave Kinematics, Molde, Norway, pp. 535–549.
Skourup, J., 1994, “Evolution and Kinematics of a Modulated Wave Train by Use of the Boundary Element Method,” Proceedings, IAHR International Symposium: Waves—Physical and Numerical Modelling, University of British Columbia, Vancouver, Canada, pp. 871–880.
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