With the emergence of the semisub-mersible tender assist drilling (TAD) unit, tender assist drilling has reached a new level. Since the mid-1980s, drilling contractors and operators have modified existing semisubmer-sible mobile offshore drilling units (MODU) on a temporary basis to operate as TAD units with great success. Starting with the Seahawk MODU conversion in 1993, the semisubmer-sible TAD concept has evolved into a reliable and efficient development option for depths as great as ultra-deepwater, outperforming its mono-hull predecessors (ships and barges) by providing the following advantages: 1. Better motion characteristics, which are particularly important during the rig-up/rig-down of the drilling equipment set (DES) on the platform and when transferring relatively large loads.
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