Global navigation satellite system (GNSS) technology has been used as a surface positioning system for approximately twenty years. Typical applications have included positioning of top-side assets, fixed installations and subsea structures.

In the late eighties and early nineties GNSS based systems were predominantly utilised as a back-up to established radio based range/range or range and bearing navigation systems. However as the availability and reliability of GNSS improved, their comparatively low operating cost and global availability has seen them become the preferred and primary method of surface positioning.

The wide availability and relative cheapness of DGNSS and services has been such that they can be perceived as a commodity. This has led to a lower priority being assigned to the selection of appropriate systems, particularly in the DP positioning sector, where the recent boom in new build DP vessels saw many companies and shipyards, new to DP classification of vessels, involved in the specification and commissioning of DGNSS. The use of inappropriate systems has led to delays in project execution, vessel downtime and in some circumstances damage to assets. The costs incurred during any of these incidents have significantly outweighed the procurement of a suitable system from the outset.

It is therefore critical from both operational and safety perspectives that there is an understanding of the key criteria to be considered during the selection process. These include available GNSS, vessel class requirements, vessel activities, performance expectations, regional variations in atmospheric conditions and contractual obligations.