Stability. Platforms are inherently more stable under most sea states 

 and would be acceptable in all but the severest conditions; however, it 

 appears possible for all reasonably sized ships to operate as a heavy-lift 

 system at least 95% of the time in all the oceans of the world. As stated 

 before, the importance of stability is related directly to the type of operation. 

 The FORDS platform would be an exceptionally stable free-floating vessel, 

 as it must be because of its primary mission of on-station testing. A T-2 

 class tanker or equivalent would prove satisfactory in all but hurricane 

 conditions. It appears unnecessary, therefore, to advocate the use of the 

 exceptionally stable surface vessels; they are considerably more than is 

 needed and would prove to be superior to less stable vessels for only a very 

 small portion of the time. 



Appendix B presents a comprehensive look into the motions of the 

 T-2 tanker, the C1-M-A VI ship, and the FORDS platform, and a less detailed 

 look at the remaining vessels of Table 2. Figure 4 illustrates an important 

 result of Appendix B, namely, the response of these vessels in heave in 

 certain sea states. The heave amplitude at various frequencies is an important 

 input for determining the dynamic stresses in the cable and pipe string 

 systems. It will be seen in the following sections that these vessels offer 

 varying yet acceptable degrees of stability. The C1-M-A VJ, the smallest of 

 the three, would probably prove to be satisfactory as a surface vessel in all 

 but the more severe environments. There is no question that a ship the size 

 of a T-2 tanker or a platform similar to FORDS would be acceptable as a 

 surface vessel in this project. For the sake of consistency and simplicity, 

 the characteristics of the T-2 tanker and FORDS \nI\\ be used where pertinent 

 in discussions of the ship and platform systems, respectively. 



Conclusions. The general feeling of the authors is that no major 

 distinction needs to be made between ships or platforms. Both would prove 

 satisfactory for the purposes of this project. As discussed earlier and in 

 Appendix B, the choice is really dependent on mission definition and 

 anticipated uses for the heavy-lift system. Each has its advantages and 

 limitations, and the final choice will undoubtedly be based on the total costs 

 of representative vessels. If one were to judge from the composition of the 

 offshore drilling fleet, a ship would probably be the chosen vessel. 



Pipe 



The possibilities of using pipe as the suspending medium are given a 

 comprehensive examination in Appendix B. Included in the analysis is a 

 look at the equipment associated with pipe handling operations. 



16 



