As offshore drilling and production goes into increasingly deeper water depths, costs can do nothing but increase as well. Drilling vessels become larger to handle drilling programs further from shore supply and tend toward Dynamic Positioning (DP). Production vessel size increases to be as self sufficient as possible due to the distance from shore supply and other support platforms, as well as employing economies of scale to produce the maximum number of wells/fields from a single platform.

This paper discusses design, installation, hook-up and performance of a totally external mooring system for drilling and production vessels to aid in cost reduction. The vessel provides only a hard connection on the hull and any line load data collection required, such as for the DP system. Winches are not necessary, freeing up valuable deck space and loading capacity. DP system operation is reduced, lowering fuel costs and exhaust emissions. Concept design information is provided with operational examples from the four (4) leg, secondary mooring system installed on the Transocean Sedco Forex semi-submersible drilling unit Deepwater Horizon.

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