A multi-connected floating body system composed of many connected small-scale floating body units has a number of advantages with regard to construction and performance. To realize the multi-connected floating body system, a new type of mechanical connecting device was developed. It is composed of multi-degrees of freedom connecting mechanism and restricting mechanism to control a restricting condition between floating body units, and its effectiveness was confirmed by model basin test in waves. Next, friction and wear tests in the seawater environment led to the discovery of suitable materials for oscillatory sliding parts in multi-degrees of freedom connecting mechanism. Finally, a field test performed for two floating body units connected by use of the mechanical connecting device proved that the developed mechanical connecting device was of practical use.

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The demonstration experiments on Mega-float off Oppama at Yokosuka has been completed in winter of 1998.There two kinds of mooring devices on mooring dolphins were adopted .Basically a rigid type mooring device is considered so that the Megafloat responds small against the wave and wind. However the sufficient breakwaters were not provided for creating a calm sea, the slack mooring system combined with a rubber damper and two lines of rubber mold chains was mainly used., while the rigid type device was used during two weeks in calm season.The paper describes the design for these mooring facilities ,such as design loads, motion response along with results measured and the enhacements carried out.

In the field of marine engineering, various types of floating bodies have been designed. Motions of them should be treated taking account of the effect of not only ocean waves but also external systems such as mooring lines, pipe lines, cables, or adjacent floating bodies.Fundamental and systematic studies were carried out on motions of a floating body under composite external loads. Widely and commonly applicable prediction method was developed to predict them.In order to verify the applicability of the prediction method, model experiments were carried out for the several typical cases of floating bodies under composite external loads. Fairly good agreements could be obtained between calculated and measured values, so that the availability of present prediction method was confirmed by experiments.Where composite external loads can be approximated by linearized dynamic system, present method will be usefully applied to the design of various type of floating bodies under composite external loads.