The tasks involved in the work of underwater maintenance, inspection and continued oil and gas field development require special equipment. This demand kindles initiative providing the incentive for the development of innovative labour-, time-, and hence, cost-saving devices. The system described in this paper is designed to provide a remotely operated underwater vehicle, primarily to assist the diver on location by providing all the tools and facilities, secondly to actually transport other tools to the worksite and thirdly as a vehicle capable of performing certain tasks in its own right as an ROV.
The vehicle system prototype, designed and manufactured by ZF-Herion Systemtechnik with the support of the Commission of the European Communities, has successfully completed a series of sea trials with Det Norske Veritas in Bergen, Norway. It is presently due for mobilization offshore onto Shell Expro's MSV Stadive to undergo trials, having been fully integrated into a specific work procedure.
The growth of the offshore industry in recent times has led to corresponding demands on the diving industry and as a result diving techniques have been developed to a degree where the task of putting a working diver at a water depth of 200 metres has become routine.
The costs involved in operating a Diving Support Vessel (DSV) equipped with the necessary saturation diving spread are however high and this factor, together with the ever present risk of accident, has created a requirement for submersible machines which can perform the various work programmes, operated by remote control from the surface.
The commercial development of such machines has been continuous since about the mid-1970s and although a number of remote controlled and manned submersibles are already available and doing useful work, for many tasks there is as yet no real substitute for the diver working on site, particularly NDT and construction work.
This situation was recognized by ZF-Herion Systemtechnik and the company set out to design and manufacture a 1; ew concept in multipurpose underwater vehicles which could be employed either as a diver assistance vehicle or as a conventional ROV.
A typical example of the equipment required to maintain a diver working in deep water would begin with a specially constructed Diving Support Vessel (DSV) of at least 2000 tons with accommodation for about 80 personnel. The vessel would carry a saturation diving chamber complex, a diving bell with appropriate handling arrangement and the various diving life support systems such as gas and hot water supplies. During diving operations it is essential that the DSV should maintain accurate position and heading above the work site and the vessel would therefore be equipped with a sophisticated dynamic positioning system.
The costs to charter such a vessel at present in the North Sea amount to approximately $20 000–25 000 each day that the vessel is on contract.
