This paper describes work performed by the Pisces VI manned submersible working off the Discoverer Seven Seas since December 1977 and employed in the record deep water drilling undertaken off the Congo. This work represents the industry?s deepest application of a manned untethered free swimming submersible supporting drilling operations. The details of the work performed should be of particular interest to operators in describing the extent of subsea support that can practically be expected during actual deep drilling operations. While initially employed as a backup system to the drill ship's remote control independent systems, the submersible evolved as a practical support tool and is used extensively. Details of the actual work performed by Pisces VI is presented in this paper and include tasks such as riser, stack, and guide base inspections; re-entry assistance; acoustic beacon. intervention work; and detailed bottom site surveys. The submersible, related equipment, and operations are described in the following report. Potential areas of work, and improved operating equipment and techniques currently under development or being installed aboard the Discoverer Seven Seas, are described.


In December 1977 the drill ship Discoverer Seven Seas prepared to move to a 4352 foot water depth location off the Congo for what would be a new deep water drilling record. International Hydrodynamics Co. ltd. (Hyco) of Vancouver, Canada was contacted with respect to providing an untethered manned submersible with the required depth capability for this particular drilling location. The Pisces VI had completed a deep recovery operation off San Francisco and was moved to Houston with its support equipment for shipment to Point Noire. Upon arrival on the Discoverer Seven Seas, Hyco's crew spent two days setting up and checking out equipment and then commenced the first of a series of dives to the well site. Pisces VI had two major task definitons: to act as a back up observation system for the drill ship's remote controlled television; and to conduct emergency salvage of BOP stack and riser. Over the past 18 month's operations no emergency salvage work has been required, but Pisces has emerged as the primary observation system and a number of additional tasks have evolved.

The intent of this paper is to introduce and describe this operation, which is the industry's first application of a manned untethered submersible supporting a deep water drilling operation. The Pisces VI and related equipment are described, together with past and new surface handling methods. The various types of work performed are described and a summary comparison of tethered and un tethered diving systems is provided.


Pisces VI is one of five deep Pisces class submersibles built by Hyco with operating depths of 6600 feet. It operates untethered 1 powered by two large battery banks, and carries a pilot and observer with optional space for a second observer.

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