A 7,500-Ton-Capacity, Shipboard, Completely Gimbaled and Heave-Compensated Platform
Authors: McNary J.F. , Person A. , Ozudogru Y.H. 
Published: December 2007

A successful deep-ocean system for deploying and retrieving kiloton loads on a pipe string from a working vessel has been developed. This paper describes the design, construction, installation, testing, and at-sea operational experiences of this unique system onboard the Glomar Explorer.

Introduction

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 great 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 drillships such as the Glomar Challenger. proficiently from drillships such as the Glomar Challenger. Because of these restrictions, subsea equipment was designed to be small and lightweight. Elaborate buoyancy schemes were necessary to accommodate weights of any magnitude.

In early 1970, a program was envisioned that would give new life to deep-ocean exploitation. The goal was to develop a capability to handle kiloton loads at oceanic depths.

The Glomar Explorer was a result of this goal. This ship was designed to lower loads of several million pounds to depths exceeding 15,000 ft using a lift pipe. pounds to depths exceeding 15,000 ft using a lift pipe. Maximum loads supported by the ship's pipe hoisting system can exceed 15 million lb. 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. To isolate the lift pipe from bending loads induced by ship motion, the load-supporting platform was gimbaled and heave-compensated.

Gimbal System

The heave-compensated and gimbaled platform provides stable support for the hoisting system' and suspended load. Its intent is to assure that minimal bending loads are induced by ship motions into the highly stressed lifting pipe. pipe. 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 Figs. 1 through 3). The heave-compensator rams are, in turn, supported by the A-frame structure that transversely bridges the ship's open moonpool. The connection between the support yokes and the gimbal ring is through two longitudinal pins and large bearings that serve as the gimbal roll pivot pins and large bearings that serve as the gimbal roll pivot axis. Each yoke rides in vertical guide slots in the A-frame structure to contain the gimbal heave (15-ft total stroke). The inner gimbal structure is connected to the outer gimbal at the pitch axis on large bearings port and starboard through pins cantilevered from the inner gimbal (see Figs. 4 through 6).

The inner gimbal, which is independent of ship roll, pitch, and heave motions, forms the heart of the Glomar pitch, and heave motions, forms the heart of the Glomar Explorer's stable-platform concept. The upper pair of hoisting cylinders is mounted on the inner gimbal. Below the inner gimbal, a cage structure is hung that serves to support the lower pair of heavy-lift cylinders. The subbase structure that supports the rig floor and pipehandling derrick is also supported on the inner gimbal pipehandling derrick is also supported on the inner gimbal (see Figs. 2 and 3). The gimbal system is capable of accommodating relative motion between the ship and pipe string of plus or minus 7 1/2 ft heave, plus or minus pipe string of plus or minus 7 1/2 ft heave, plus or minus 8 1/2 degrees roll, and plus or minus 5 degrees pitch.

JPT

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