Wind And Wave Measurements From The First Year Of Drilling In The Baltimore Canyon

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Abstract
From April 1978 through February 1979, wind and wave measurements were made from the Western Pacesetter II while it was drilling in the Baltimore Canyon area approximately 100 miles off the coast of New Jersey. An anemometer was mounted at the top of the drilling derrick and a Wave rider buoy was moored nearby. Approximately 20 minutes of data each three hours were recorded by a microprocessor based digital recording system onto cassette tapes. The data has been processed to yield average wind speed and direction, significant wave heights, and wave spectra. Seasonal and summary statistics have been developed which show, for instance, that a significant wave height of ten feet was exceeded 8.5 percent of the year. The highest measured significant wave height during the year was 19.5 feet. These statistics should be useful in planning future operations in the area. Study of the high frequency portions of the spectra revealed that over a substantial range, it was inversely proportional to the fourth power of the frequency and directly proportional to the wind friction velocity. The classical inverse fifth power equilibrium range appeared only for frequencies substantially above that of the spectral peak. Using these observations, it was possible to produce a consistent representation of the high frequency tail of the spectrum which should be useful for developing criteria for structural fatigue studies. INTRODUCTION During 1978 and the early part of 1979, Shell was one of a number of operators who tested leases which had been acquired in the Baltimore Canyon area off the coast of New Jersey (Figure 1). The drilling was done from the Western Pacesetter II. Since the entire east coast of the United States is essentially a frontier area for offshore drilling, additional environmental data on the area is very useful for planning future activities. Thus, in addition to participating in the joint industry instrumentation project described by Rose et al. (1979), we decided to make wind and wave measurements from the Pacesetter II. Since most of the instrumentation needed was already on hand, it was possible to start making measurements in April, shortly after the rig moved on site. Because of the simplicity of the instrumentation, a reasonably complete data set was collected even though the system was operated without regular service checks. The measurements add significantly to the marine climatology data base for the area, as well as providing some interesting information on the characteristics of the high frequency tail of the wave spectrum. We begin by discussing the instrumentation and its installation on the Pacesetter II. Our operating experience with this system may help others plan similar measurement programs. The data was first processed to yield histories of the significant wave height and wind speed and direction. From these histories, we calculated seasonal and summary exceedance statistics.

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