A very large floating structure is now being considered as a possible candidate of an offshore airport. The structure is expected to be so large that the analysis of the hydrodynamic forces that will act on the structure by a conventional numerical technique is practically impossible because of the required huge computational burden. In order to overcome this difficulty, an approximate but quite accurate numerical method for the analysis of a diffraction problem was presented in the 1st report. The method exploits the fact that the structure is very large and assume a certain uniformity in the flow field around the structure except at the vicinity of the perimeters of the structure. The present paper extends the method to the analysis of a radiation problem (including that due to elastic motions) and shows that a similar approximate technique can be used in the analysis. In addition, as examples of the application of the presented method to some practical problems, an analysis of elastic responses of a very large floating structure in waves and an analysis of wave forces on a floating airport composed of two runway structures are carried out.