Development, Testing, and Operation of a Large Suspended Ocean Measurement Structure for Deep-Ocean Use
Authors: Fagot M.G. , Swenson R.C. , Howell T.A. , McCardle G.D. , Walton D.L. 
Published: October 2008

A large, suspended ocean measurement structure was developed and operated. The structure was a tripod configuration 5100 m high with a base footprint of 6190 m, all of which is suspended by a single 6150-lb buoyant float. The three 6200-m-long legs contained environmental measurement instrumentand engineering sensors located in the top 2150 m of the legs. communication With the system was via a single steel coaxial cable, which also moored the Tending vessel during operation. This paper focuses on the ocean engineering for developing, tearing, and operating the system. A new, lightweight cable resign Facilitated storage, deployment, and retrieval of more than 18,600 m (10 mni) of cable from a relatively small, 2 10-foot-long tending vessel. The deployment scenario was optimized to allow this single vessel to transport and deploy over 67 tons of system equipment. An acoustic positioning system was employed to "fly" the 7000-lb anchors to precise bottom location. The system was the largest ocean measurement structure to be successfully deployed its the deep ocean (52MI m).

INTRODUCTION

'TheNavy has the need to deploy large measurement systems in deep water for monitoring environmental parameter. Some of these sisters must span the complete water column and provide a stable structure for performing the measurements. The measurements need to be monitored in real time to provide the scientist with fhe ability to alter other experiment assets with changes in the environment. Such a requirement existed for a system to be used in a summer 1991 experiment. This led to the development, testing, and operation of a buoyed, suspended, three-legged tripd cable structure 5100 m high and a base footprint of6190m.

Background

In 1969, a large, three-legged structure was deployed in 3 miles of water. The structure consisted of three each 4-mile-long cable Iegs, three 23,000-lb rmchors, a 26,000-lb buoyant apex buoy, and approximately 4000 glass floats attached to the legs to render them neutrally buoyant. The toraf equipment load on the deployment vessel was 425 tons. A second sh-nplcr structure, but of the same magnitude, was deployed in 1970. Both structures failed to produce data due to steel armor cable kinking, conductor insulation lack of integrity and the general difficukics in deployment. The conventional technology base of steel double-armored well-logging cable simply did not meet tie requirements of Icing, suspended, neutrell y buoyant cables populated with a multiplicity of sensors.

Thus, in 1971, the Navy initiated a program to develop the components and techniques to meet this explicit requirement. 'Iris program ultimately produced The Kevlar instrumented cables and fee torque-free, lightweight steel cables now commonly used today. Although many irrstmmented structures and systems used rhis revolving technology base irr the ensuing years, the Navy's vcrticel instnrmented cable system deployed its 1988-1989 clearly &monstrated the feasibility of future volumctnc stmctnres at modest cost and deployment scenarios.

This structure consisted of a single moored vertical instrumented cable, which spanned the water column in 3 miles of water a mass weight anchor and 5 miles of spaced armoq 0.69-inch coax cable, which served the multiple functions of lowcrirrg the anchor to the seafloor, mooring the structure-rending ship, end eommrnticating with the multiplexed instrumented cable system. This single example clearly showed that a multiplicity of legs could be deployed, utilizing the same ccmpcetents and procedures.