The influence of wave forces on the design of offshore structures for the oil industry

Until after the second World War, the ocean was regarded by the oil industry only as a cheap means of transportation. Before the war some timber structures very close to the shoreline had been constructed, but drilling for oil on the continental shelf did not really start until 1947, when the first steel platform was erected in 20 ft. of water in the Gulf of Mexico. In the following twenty years, rapid progress took place not only in the number of constructed platforms, but also in the water depths in which these structures were placed. In 1955, 100'was reached, 200' in 1959, 285! in 1965 and in 1967 a platform was placed in 340' of water. This is certainly not the end. Platforms for 600' of water are technically feasible and are already on the drawing boards. For exploration drilling, movable structures are preferred and these units have been constructed in great' variety - jack-up units with from three to ten legs and submersible units, all still bottom supported when drilling. Floating units have also been developed - boat-shaped vessels, barges, catamarans and finally the semi-submersibles. Anyone who follows the patent literature will find a continuous stream of inventions in this field. The designer of these structures is confronted with the problem of constructing them in such a way that they are able to withstand without significant damage the loads imposed by the environmental conditions, by "environmental conditions" we generally mean waves, winds and currents, but ice floes and earthquakes can also be included. In this paper we will limit ourselves mainly to wave forces