Self-elevating mobile drilling or accommodation platforms, generally referred to as "jack-ups" have been on the offshore scene in some form or other for many years.

In recent years the range and capability of such structures has extended to enable them to operate in water depths of greater than 400 feet, and in areas with very severe meteorological conditions.

At the same time designers have made great efforts to avoid concomitant in-creases in costs by paying great attention to the structural design of legs, jack frame, jacking system, and hull. Whereas the aoplication of static design methods have been successful in water depths up to above 300 feet, increasing the allowable water depth above this necessitates the detailed consideration of dynamic effects and foundation behaviour.

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