INTRODUCTION
Definition

A guideline system consists of mechanical cables that restrict the lateral drifting of a payload suspended from a flexible lift line. The guideline system is composed of four basic components: surface support, guideline, anchor, and guide frame (Figure 1). The guideline is either a steel or a synthetic rope which stretches in a near vertical orientation between the surface support and the anchor. The guide frame is a rigid truss which maintains 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.

Objectives

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 hardware design, motion analysis, and at-sea operation. Once sufficient field data were obtained, then procedures for the design, deployment, and operation 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 by adding modular weights to the anchor after its implant, and that the alignment of the modules could be controlled by a properly designed guideline and bottom guide posts.

Background

Future underwater construction and salvage operations may require extensive load-handling capabilities for emplacement, suspension, recovery, and assembly of large, heavy structures at predetermined seafloor locations at depths to 20,000 feet. 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. Guideline systems are a potential solution for these problems.

The concept of a flexible guideline system is simple and inexpensive; yet, it is an effective means of restricting the lateral motions of a payload throughout its vertical travel in the water column. The components of the system are readily available as off-the- shelf items. How ever, the most serious draw back to the system is believed to be its apparent low rehab1hty wh1ch 1S caused manly by line entanglement.

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