The operational experience gained from the offshore application of free-swimming remotely operated vehicles (ROVs) to perform cable and flowline burial operations has yielded interesting results Several lessons have been learned to improve future systems Other experiences have enabled the pilots to more effectively perform the required tasks Yet other factors indicate that the present state-of-the-art of some of the systems is insufficient to provide optimum performance of the system in all bottom types and all conditions encountered.
During the past fifteen months, Ocean Systems Engineering (OSE) has delivered two off 150 Hp work based free-swimming ROV systems complete with jetting skids for cable and flowline burial, an additional jetting skid has been designed and interfaced to an existing ROV, and a system is under construction which will represent the most powerful, most versatile capability built to date. During this time, we have had the opportunity to Interface closely with the owners and operators of the systems to take advantage of the operational experience being gamed through the use of the systems
The operational experience base has allowed us to improve each successive system and each successive operation over the prior one The areas of Interest can be divided as shown below
For the purposes of this paper, only those factors relating directly to jetting, excavation, and burial operations will be discussed. The normal Improvements which take place over a given period of time with any new system have not been addressed
It is necessary to have a basic understanding of the system and the operations to understand the significance of the Issues presented below The HydraTmAT 1850 CRS is a 150 Hp electrohydraulically powered system with dual heavy duty manipulators, a full suite of television cameras, sonars, cable/pipe track, and navigation equipment Microprocessor based control system, computer based diagnostics, extensive operator graphics screens and fiber optic main umbilical make it the most advanced, most work capable ROV available. The basic ROV system is configured so that the jetting system is a neutrally buoyant skid package which derives its hydraulic and electric power from the vehicle. The skid package can be easily removed for maintenance or to enable the vehicle to be used alone for search, tracking, survey, and other non-burial missions This allows the vehicle to be operated in the state which allows the maximum maneuvering performance whenever required. It also allows differing specialized work packages to be installed on and used by the vehicle when the situation so requires
The jetting kid package is designed to enable a variety of soils to be jetted during a single dive without the necessity to resurface to change nozzles or tools. The jetting system is equipped with a series of two rows of nozzles which include both low pressure and high pressure jets. This arrangement enables the operator to customize the jetting configuration from the console to attain the highest efficiency possible in the soil type being encountered. Since the soil type can change dramatically over the course of a dive or a day's operations, this feature speeds the overall burial processand eliminates the time which would otherwise be required to return the vehicle to the surface, modify/change the system, redeploy the system, relocate the position where jetting operations ceased, and resume the jetting operation