With the object of improving the safety and structural reliability of offshore structures and to provide data to assist the Government in the framing of legislation and certification procedures for offshore operators, the Division of Maritime Science at the National Physical Laboratory recently placed a research structure on the seabed in Christchurch Bay off the south Coast.
The site was chosen because the sea conditions in the area in relation to the size area of the research structure will provide, in a comparatively short time, data on average and peak wave conditions likely to be experienced over much longer periods by full-sized offshore structures of the type used in Northern water.
Some of the data will be processed by an ‘on board’ computer with the ability to record over 2 million items of information in 20-minute sequences, and to transmit this information by radio link to the land base for immediate analysis. Recorded tapes of raw data will be collected periodically for detailed study.
The research structure is in the form of a steel column 16 metres high and free standing in a mean water depth of 8.4 metres. The segmented column is instrumented to fulfil a two-year programme of comprehensive measurements of the forces and pressures exerted by the winds, waves, and currents on the 60 tonnes structure, its 200 tonnes gravity base, and supporting seabed.
The column is secured to the circular steel plate encased in the concrete base by eighteen 1.7/8” diameter studs and nuts of FERRALIUM 255 (UNS S32550, Alloy 255, DIN 1.4507, ASTM F61) because of this super duplex stainless steel’s high strength allied with excellent corrosion resistance properties in marine applications.
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