Anchor monitoring system

Abstract

A system wherein a vessel (12) is moored by catenary mooring lines (14, 15, 16) that include polymer cable lengths (30) that can stretch under tension, which indicates the amount of polymer stretching. In the absence of polymer line stretching, a measured actual drift or excursion of the vessel from its initial position (as determined by a GPS system) would result in a predetermined nonstretch inclination (graph 50) of the top (42) of a first mooring line (14) from the horizontal. If the inclination is greater than the predicted nonstretch inclination, this indicates that the polymer line has stretched, with the amount of stretch indicated by the increase in inclination over the predicted nonstretch inclination.

Description

CROSS-REFERENCE[0001]Applicant claims priority from U.S. Provisional patent application Ser. No. 60 / 995,953 filed Sep. 28, 2007.BACKGROUND OF THE INVENTION[0002]A system for mooring a vessel in deep water (e.g. over 500 meters depth) can include mooring lines that extend in catenary curves and in different compass directions, from the vessel to the sea floor. The mooring lines limit vessel drift from an initial position to avoid damage to a riser that extends from the vessel down to the sea floor. The mooring lines may include long (over 250 meters length) polymer cable portions in addition to shorter steel chain portions, to limit the weight in water of the mooring line and the consequent line tension. For example, a cable of polyester has a density of about 1.3, which is close to that of water (density of 1.0), so the cable adds only moderate weight and consequent tension to the mooring line in water. However, one problem encountered in the use of polymer cables is that they commo...

AI Technical Summary

Benefits of technology

[0004]In accordance with one embodiment of the invention, a method and system are provided for mooring a vessel using catenary mooring lines that include polymer cables, which indicates the amount of any stretching of a polymer cable. An inclinometer is attached to the upper end of the mooring line, and changes in the inclination from the horizontal are monitored. Drift of the vessel from its initial posit

Problems solved by technology

However, one problem encountered in the use of polymer cables is that they commonly undergo permanent elongation (plastic deformation) when subjected to large tension, as during large storms.

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