Guidelines for the shared use of DGPS (differential global positioning system) for DP (dynamic positioning) and survey operations have been published by the International Marine Contractors Association. The operational straightforwardness of differential global navigation satellite systems (DGNSS) has led to its permanent installation and widespread use aboard DP vessels without input from surveyors. This has given vessel operators significant autonomy regarding the positioning of their vessels. When survey services are required on board, the survey contractor is often asked to make use of the DGNSS system permanently installed on the vessel.

Whilst usually convenient, this can present potential operational problems relating to the control and performance of the system. There is also potential for contractual disputes to arise in any situation where the survey user and the DP user are different companies and where installation, manipulation or reconfiguration of the positioning system for either survey or DP use may impact on the performance of the system for the other party.

The new IMCA publication addresses all these issues, which are critical from both safety and operational perspectives. The guidelines were produced following discussion and consultation between our Offshore Survey and Marine Divisions. They set out basic definitions before going on to consider the differing requirements of both surveyors and DP operators. They highlight the potential problems relating to control and performance of the system and the need for planning and co-operation to avoid conflict and ensure safety; and conclude with a set of recommendations for those considering sharing systems.