The project described here covers the second phase of a program referred to as the MARS project. The final goal of the complete project is to produce a submersible vehicle system to be used generally for tasks associated with subsea inspection, maintenance and repair work in situations where to employ a diver would be either too dangerous or uneconomical. The system is therefore intended to work as far as possible under remote control from the surface. Because certain tasks cannot however be completed using such a remotely operated system, it is intended that the MARS vehicle should be capable of quick conversion into a form suitable for diver assistance for use when diver intervention becomes unavoidable.
Phase 1 was concerned with establishing the system concept and specification.
Phase 2 relates to design,development,manufacture and testing of components and modules, with subsequent integration into a basic vehicle arrangement to form a complete working system.
Components
The individual components for the MARS system were designed and manufactured according to the specifications defined as a result of the work carried out in Phase 1. After subsequent testing it was found necessary in certain cases to carry out further modification work as follows :
Power supply system : Fitting of capacitors for the reduction of reactive power.
Umbilical winch : Modification to the spooling drive.
Umbilical termination : Use of alternative resins to reduce the time required to complete a termination.
Fitting of an umbilical bending protector.
Docking claw : Improving the mechanical strength of various component parts.
Propulsion units : Redesigning the propulsion units for improved service life.
Handling system : Investigation showed that for financial and operational reasons, the design and development of a universal handling system could not be justified. It was found that a handling system could be constructed only to suit particular vehicle parameters.
Manipulator : The manipulator type and arrangement was selected to suit the requirements described by the varous offshore service companies. A 7-function master/slave manipulator system was integrated into movable manipulator module for attachment onto the top of the vehicle.
Tests
From the many tests carried out during the duration of the project, the most useful information was gained when the system was operated from the Seaway Condor. This trial enabled the system to be tested over a longer period of time working in actual offshore conditions . For this trial, the vehicle was arranged as a diver assistance system without the manipulator.
Trial results : The vehicle system displayed various faults which were corrected on board the vessel. Typical problems were loss of signals from the diver's control station and water jetting module, data-link faults, leaks in the hydraulic system and failure of the main electric motor. The trial duration ran through a total of 1 ,032 hoursand within this period the vehicle was eiter operating or available for operation for a total of 818 hours to achieve 79
. 3 % reliability. Service work needed for fault correction required 127 hours (=12. 3%), and time waiting for spare parts amounted to 72 hours (=7%).
Faults occuring in the first half of the trial period accounted for 127 hours of non-operational time but no further significant downtime was recorded during the second half.
The purpose of the MARS 2 project was to manufacture and test the MARS vehicle as a complete system which would be designed to incorporate the knowledge and experience gained from the MARS 1 project. The required project work waqs carried out in various stages as follows :
Design and manufacture of individual mechanical and hydraulic components. Pressure chamber and tank testing of components.
Integration of components in a DAVID submersible vehicle.
Study work to define system design and parameters for the vehicle control system.
Design of the control system.
Offshore trials to assess the relative performance of the various individual components when operating together with the vehicle module.
Integration of the components into the MARS carrier vehicle. Defining the manipulator equipment for the vehicle according to the type and situation required for the vehicle.
Offshore trials for the complete MARS vehicle system, without the manipulator.