Measured Wave Force Data On Offshore Platforms
Authors: Thrasher L.W. , Aagaard P.M. 
Published: December 2007

When a hurricane wave smashes into a platform, how big is the wave and what force does it exert? In designing the platform, how strong is strong enough? In a joint effort, several companies set out to answer these questions, and much of the data they collected in the process have been made publicly available.

Introduction

During the 1950's, a Gulf of Mexico platform designer needed especially strong nerves. He was designing drilling platforms for a multimillion-dollar investment in the hurricane belt, but did not know what would happen when those hurricane waves smashed into his platform. How big are such waves and what force do platform. How big are such waves and what force do they exert? He had asked this question of oceanographers and ocean construction men who offered calculation schemes but had little actual data on wave heights, wave forces, and tide levels that he could use for design. Recommended wave force values had a 4 to 1 spread. The only way the designer could decrease that spread was to place instruments in the ocean and measure the waves. Designers in several oil companies took that step. Table 1 lists some of the wave measurement projects that were started. The construction and operation projects that were started. The construction and operation phases alone of those projects have probably cost the phases alone of those projects have probably cost the industry more than $2 million, and the data obtained are the most nearly complete and accurate available today for platform design. Our purpose here is to describe the information obtained in two of the listed projects, Wave Projects I and II, operated by Standard Oil Co. of California, and to announce the availability of the measured data.

The Installations

The wave measurement installations were located in the Gulf of Mexico because the immediate design problem was there, and because hurricanes occur problem was there, and because hurricanes occur there frequently, generating the large waves that so greatly affect platform design. Fig. 1 shows the locations of the two installations. The first installation, Wave Project I, was completed in late summer, 1954, on Chevron D platform, Bay Marchand, in about 30 ft of water. Data were obtained during five hurricanes and many smaller storms. After more than 4 years of operation, the instruments were dismantled at the end of the 1958 hurricane season. A study of the data obtained during Wave Project I indicated that further measurements were warranted. To obtain data from larger waves in deeper water, a second installation, Wave Project II, was placed in operation in late summer, 1960, on a placed in operation in late summer, 1960, on a Chevron platform at South Timbalier Block 63. The water depth is about 100 ft. Data were obtained during Hurricane Carla, 1961, and numerous smaller storms, and the instruments were dismantled at the end of the 1963 hurricane season. The tracks for all six hurricanes that generated large waves at the two installations are plotted on Fig. 2. Participation in both projects was offered to the industry on a cost- and risk-sharing basis.

JPT

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