The differential global positioning system (DGPS) has made an enormous impact on vessel navigation and positioning over recent years. DGPS offers better quality, consistency and flexibility than other positioning systems, and can also offer direct "absolute" positioning of vessels. Most vessel activities in the offshore industry have benefited from the use of DGPS and it is used extensively as a vessel position reference in dynamic positioning (DP) activities. In many DP configurations it is one of the main position references. The alternatives - taut wire and acoustics - both have limitations.

However, no system is 100% reliable, and users need to understand DGPS characteristics to improve their confidence in its performance. Quality monitoring is also importnat for all activities using DGPS. With this in mind, this report summarises best practice for DGPS in DP control systems, and makes some key recommendations and proposals to improve DGPS reliability for DP applications. The guidlines, which are aimed primarily at the suppliers and operators of DGPS and DP control systems and the owners or managers of DP vessels, are intended to:

• assist optimum DGPS use and improve reliability
• promote the use of a standard interface between the DGPS and DP control systems
• improve the use of DGPS quality control indicators in DP activities
• recognise the importance of DGPS training for DP operators
• provide a basis on which DP classification authorities can formally approve DGPS as a DP position reference
• provide a means of bridging the gap between theoretical DGPS documentation and DP vessels' procedures and quality systems
• distil current best practice into guidance and further improve DP users' confidence in DGPS.

In addition to being a bridge between theory and operating procedures, it is intended that this document will form a base for further improvement in the application and documentation of DGPS in DP activities.