Dynamic Positioning

Positioning offshore supply vessels in close proximity to moving oil and gas production facilities, like tension-leg platforms, is traditionally performed using multi-point anchor systems. These anchor systems protect the rig structure from collision damage, but limit the number of unloading positions around the rig and consume valuable time to attach and release the supply vessel. The use of advanced dynamic positioning algorithms and highly accurate GPS-based position data allow an offshore supply vessel to approach and hold station during unloading without anchors. In December 1998 and February 1999, Seatex installed DARPS (DGPS Absolute Relative Positioning Sensor) on two offshore supply vessels with Simrad dynamic positioning systems. The DARPS system provides two GPS based positions to the DP system-- a DGPS fix using IALA corrections and a target distance/bearing calculation. The relative distance and bearing calculation is not dependent upon differential corrections, thus making the system more robust. The integration of the positioning data with the DP controller allows the offshore supply vessel to work more safely, in higher sea-states, and at multiple loading locations around the platform