INTRODUCTION 



Future underwater construction and salvage operations for the Navy 

 may require extensive load-handling capabilities for emplacement, sus- 

 pension, recovery, and assembly of large, heavy structures at predeter- 

 mined seafloor locations at depths to 20,000 feet. Guideline systems 

 are a potential solution for these problems. The required capabilities 

 include not only high-tension lifting but also seafloor positioning and 

 mating. In general, new load-handling systems must minimize the dynamic 

 loading in the lift line and the large amplitude oscillatory motion of 

 the payload near the seafloor. Additional hardware is needed to provide 

 the required capabilities for accurate seafloor positioning, precise 

 alignment, and repeated returns to the same seafloor site. 



Description of the System 



A guideline system employs mechanical cables to restrict the lateral 

 drifting of a payload suspended from a flexible lift line and is com- 

 posed of four basic components (Figure 1): surface support, guideline, 

 anchor, and guide frame. The guideline is either a steel or a synthetic 

 rope which stretches nearly vertical between the surface support and the 

 anchor. The guide frame is a rigid truss for maintaining a fixed distance 

 between the payload and the guideline. As the payload is raised or 

 lowered by a lift line, the guide frame slides freely along the guideline. 

 The lateral motion of payload is, thus, controlled by the guideline 

 system. The number of guidelines in a system can vary from one to several 

 depending on the degree of restriction of motion desired. Figure 2 pre- 

 sents a dry-land simulation of a test of a double guideline system. 



Objectives of the Sea Tests 



The purpose of this investigation was to obtain a better understanding 

 of the behavior of guideline systems by conducting controlled sea tests. 

 It was intended to identify the difficulties and problems involved in hard- 

 ware design, motion analysis, and at-sea operation. Once sufficient field 

 data were obtained, then procedures for the design, deployment, and opera- 

 tion of guideline systems could be established for future projects. 



The main emphasis of this study was on reducing the probability of 

 guideline entanglement. Field tests were designed to show that with proper 

 precautions, guideline systems could be operated without line entanglement. 

 As a secondary interest, the mechanism of mating two structural modules 

 on the seafloor by using a guideline system was studied. It was intended 

 to demonstrate that the capacity of a gravity anchor could be increased 



