Both dynamically positioned (DP) vessels and four-point moored vessels can be used in shallow water for diving support work. Remaining on position is important for both types of vessel, however, there are significant differences between them. A moored vessel is held passively on position with no possibility of recovery if a mooring line fails. A DP vessel is held actively in place and offers good recoverability possibilities if its equipment is reliable.

This report compares the station-keeping risks of the two types of diving support vessel (DSV). The study uses historic data of DP incidents and mooring line failures. It also employs mooring line data from semi-submersibles as these are more widely available than data for DSVs.