GB1428610A - Method and apparatus for transporting and launching offshore tower - Google Patents

Abstract

1428610 Pontoons for offshore structures; ballasting pontoons BROWN & ROOT Inc 18 Feb 1974 [25 April 1973] 7281/74 Headings B7A and B7M [Also in Division E1] A steel jacket 20 for an offshore platform is transported from its building dock to the offshore site on a pontoon raft 100 of floatation tanks and upon reaching this site a first set of chambers are flooded so that one end of the raft performs a crash dive to rapidly pitch the jacket 20 from the initial horizontal position to the inclined position in which two spherical buoyancy tanks 260, 262 located on a base portion of the jacket 20 are awash (Fig. 13B) and thereafter further chambers within the tanks constituting the raft 100 and the spherical tanks 260, 262 are flooded to firstly place the jacket 20 in a vertical position and then lower it on to the sea bed. The raft 100 is detached from the jacket 20 by detonating a first set of explosive charges to release connections between the raft 100 and jacket 20 and thereby permit the raft 100 to pivot about pivot connections 236 into a vertical position (Fig. 19B) and then further charges are detonated to fracture the connections 236. The raft 100 is then towed away still in its vertical position until clear of the jacket 20 and then the tanks are vented to raise it into the horizontal position on the surface. Construction of raft.-The raft comprises two mutually inclined floatation members 106, 108 internally divided into chambers 150 by bulkheads 148, two outboard auxiliary floatation members 110, 112 also internally divided into chambers 168 by bulkheads 166, bifurcated floatation members 114, 116 constituted by tubular parts 170, 172, 174, 176 again internally sub-dividedby bulkheads 202, 204 and interconnecting tubular columns 122, 124, 126, 128, 130, 132, and 138, 140, 142, 144, 146. These floatation members and columns are provided with conventional ballasting and deballasting valves, ballast sensing devices and control lines therefor as are aslo the spherical tanks 260, 262. The jacket 20 is connected to the raft by vertical pillars 222 spaced along the length of the members 106, 108 and similar pillars 223 on the columns 122, 124 126, 128, 130 and 132. The free ends of the bifurcated floatation members are interconnected by bridges 230, 232 which carry vertical columns 234 including the pivots 236. The explosive charges surround these pillars 222, 223 and columns 234.