Patent GB-1241776-A (GB)
Title: Load indicator for mooring line
IPC: G01L5/04
Filed: 1969-06-02
Abstract: 1,241,776. Measuring tension. GLOBAL MARINE Inc. June 2, 1969 [June 5, 1968], No.27730/69. Heading G1W. A method of measuring (adjacent the vessel and approximately) the tension in a mooring line extending from an anchor to a point of support on a vessel disposed in a body of water is based on the properties of a catenary by assuming that the chain or wire rope used to moor the vessel behaves as a perfectly flexible line wherein the tension To would be determined by the following parameters: - w the weight per foot of line in water e.g. sea water S the length of line paid out h the vertical distance between the anchor and support on the vessel P a parameter whose value varies with L the horizontal distance between the anchor and support e.g. # the angle of declination of the line below the horizontal. Accordingly (i) graphs are produced of the functions relating To, h and P for lines with given paid out lengths S and physical characteristic w for reading off the value of To after measuring h and P for a line where w and S are known or (ii) a signal is generated to represent # and modulated by additional signals representing w, h and S according to the function relating To to these parameters and the result displayed in terms of tension. Apparatus, Fig.2, for measuring # comprises a shoe 31 straddling the chain 26 and releasably secured to the vessel by nylon rope 40 laced through eye-bolts 41. An arm 31 with a plate 37 pinned thereto pivots on a bolt 34 in a bracket 32 on the shoe 31 and pivots on a horizontal bolt 38 in a bracket 36 which pivots on a vertical pin 39 in a chock 28, through which the chain 26 extends from a winch 27. A pointer 44 on the plate 37 indicates the angle of declination 6 on a scale 43 secured on the bracket 36 or alternatively rotatable on the bolt 38 and counter balanced so as to seek a horizontal position. The tension To can then be read off a graph Fig.3 (not shown), against the measured value of # or a removable scale card Fig.7 (not shown) of plastics or celluloid can be clipped to the bracket 36, the scale having graduation rings for a range of values related to h and constant tension value curves extending generally radially against which the pointer indicates tension directly, a set of scale cards being required, one for each size of chain. A potentiometer-type inclinometer 60 on the shoe 31 can be used to generate electric signals representing # for transmission e.g. to the bridge where they can be applied to an amplifier 62 and fed to a read out device 63 e.g. a strip recorder calibrated to indicate slope or tension. Corrections can be applied by a computer 64, for inaccuracies due to pitching, rolling and heaving. The logic network, Fig. 8 (not shown) for an automated system is described. A simplified apparatus, Fig.4 (not shown) for measuring # on small river boats employs a scale secured to the boat for direct co-operation with a straight edge of a shoe straddling its mooring line. An extimation of # can be made by counting the number of links of the chain between the support and the surface of the water and using a graph, Fig. 5 (not shown), relating the angle # to the height of the support above the water and the number of exposed links. The distance L could be measured e.g. by echo sounding and a graph, Fig. 6 (not shown), relating To and L could be used to read off the tension.