Dynamic positioning systems can operate with one or more position references on line, and it is normal for operations to have at least three systems working at any one time. Ideally these systems should be different (e.g. differential global positioning system (DGPS), acoustics and taut wire) so that no common mode of failure can leave the vessel without references.

In most DP operations the failure of one position reference is a minor disturbance. However, in some deepwater locations it is difficult to have three different references operating because taut wires are seldom accurate enough beyond 500 m and some acoustic systems are unsuitable.

In this report, dual acoustic configurations are examined. The study attempts to look at acoustic systems that are currently available for deepwater demands, but it is acknowledged that this is a fast-moving market, and new products are constantly entering it.