A deep ocean working vessel to deploy and retrieve kilo ton loads on a pipe string has been successfully designed, built, and operated. To minimize ship induced stresses in the pipe string, the load supporting platform is passively roll and pitch gimballed and heave compensated.
This paper discusses the design, construction, installation, testing and at-sea operational experiences of this unique system on the GLOMAR EXPLORER. Design parameters and constraints are presented together with special concepts which were incorporated. Solutions to the challenging construction and operational questions are also discussed. Results of actual at-sea operations are included.
The viability of a large shipboard load supporting gimbal system has been demonstrated., possible future applications include deep water installation of heavy equipment, deep and large hole drilling, pipe laying, seabed mining, salvage, etc.
Just a few years ago, technology for performing heavy work in the deep oceans was rather limited. The size and weight of equipment that could be handled and lowered from a surface vessel to deep ocean depths was a primary restriction. Oceanographers worked primarily with winch and cable systems with capacities limited to a few tons. Somewhat larger loads could be handled more proficiently from drill ships such as the GLOMAR CHALLENGER. Because of these restrictions, subsea equipment was, by necessity, designed to be small and lightweight. Elaborate buoyancy schemes were necessary to accommodate weights of any magnitude.
In early 1970, a program was envisioned which would give new life to deep ocean exploitation. The goal was to develop a capability to handle kilo ton loads at oceanic depths.
The GLOMAR EXPLORER was born out of this requirement. This ship was designed to lower loads of several million pounds to depths exceeding 15,000 feet on a lift pipe. Maximum loads supported by the ship's pipe hoisting system can exceed 15 million pounds. In order to achieve such load capacity, a highly sophisticated pipe string design was required. This weight-optimized, tapered pipe string is designed for high tensile loads with very little margin for bending loads. In order to isolate the lift pipe from bending loads induced by ship motion, the load supporting platform was gimballed and heave compensated.
The heave compensated and gimballed platform provides stable support for the hoisting system and suspended load. Its intent is to ensure that minimal bending loads are induced into the highly stressed lifting pipe due to ship motions.
The gimbal platform consists of an inner-(pitch) gimbal ring and an outer (roll) gimbal ring. The outer gimbal ring is supported on the heave compensator rams forward and aft through support yokes (see Figures 1, 2 and 3). The heave compensator rams are in turn supported by the A-frame structure which transversely bridges the ship's open moon pool. The connection between the support yokes and the gimbal ring is through two longitudinal pins and large bearings which serve as the gimbal roll pivot axis.
