NORMALLY there are only two types of marine machines concerned with the discovery and recovery of oil from under the ocean floor. The first, mainly engaged in the discovery of oil, is a self-propelled vessel, sometimes of very considerable size. Apart from its towering drilling derrick, it is indistinguishable from any oceangoing cargo vessel; its purpose is to drill boreholes in areas where seismological and geological studies suggest oil may exist. The technical operation of this activity is highly complex, yet these vessels have achieved a remarkable level of success. However, they suffer from two major drawbacks. Although they are equipped with the most advanced and sophisticated navigational equipment, including bowthrust propellers, for them to maintain position in running seas, strong tides and winds when boring can be extremely difficult, and in really heavy weather operations have to be suspended.

For the actual drilling of oil and its recovery— principally its recovery—the so-called «jack-up system» is in almost universal use. This system has to be towed into position, and consists basically of a platform which carries the drilling rig, cranes, helipads and all essential services, including living accommodations, and is attached to the seabed by firmly anchored legs. In normal conditions it is extremely effective, but like the discovery ships it has drawbacks. It is not mobile. It has to suspend operations in even moderately heavy weather. And it can be used only in comparatively shallow water: the deepest is in the North Sea, where most of those rigs are to be found. This North Sea rig stands in about 450 feet of water, and the cost of increasing the length of those legs would be so prohibitive as to make oil recovery quite uneconomical, even though Americans have plans to construct a rig with 800-foot legs off the California Coast. There is also the unknown safety factor. Two such rigs have already been lost in the North Sea. The cause of those disasters has not been clearly evaluated, although it is suspected, obviously