NL6912916A - - Google Patents

Abstract

1,250,068. Laying pipes underwater. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. 25 Aug., 1969 [26 Aug., 1968], No. 42144/69. Heading F2P. In laying a pipe-line along a preselected route on the floor of a body of water from a pipe-laying vessel having a laterally rigid or a hinged segmented laterally flexible pipe support structure extending outboard of the vessel for directing the pipe-line into the water, the loads imposed on the pipe support structure are sensed, the vessel heading is turned in dependence of the load sensed to reduce the loads on the pipe support and the vessel is moved along the preselected route while maintaining the vessel heading in the turned attitude. The adjustments in vessel heading may be carried out automatically. The load sensed may be the sideways force on the pipe support near its outer end and/or the bending moment at the inner or outer end of the pipe support. The vessel heading may be turned sufficiently to substantially eliminate the stress in the pipe or to reverse the bending moment in the pipe-line at the tip of the pipe support. The loads may be caused by transverse water currents or by misalignment of the vessel and the pipe support with the pipe-line already laid. In a preferred method the difference between the measured force and a desired force is used to generate a heading error signal proportional thereto, the difference between the tension in the pipe and a desired tension generates a tension error signal, the deviation of the vessel from the desired route generates a route error signal and these signals are combined and applied to vessel positioning means in such a manner to turn and/or move the vessel so as to restore the various values to the desired values and hence the error signals to zero and at the same time the timing and the rate of vessel move-up along the route is controlled by controlling the timing and rate at which the pipe is allowed to be payed out or reeled in. The vessel positioning means may consist of a number of rotatable thrust units suitably arranged either with or without conventional propulsion units or a plurality of anchors arranged around the vessel with controllable winches.