- The offshore community has invested a great deal in the analysis and design of compliant deep water platforms such as tension leg platforms (TLPs) and more recently spar platforms. Tension leg platforms are designed to have large overly buoyant hulls which are connected to the seafloor by slender tensioned structural members called tendons. By adjusting the tension in the tendons the draft of the hull can be adjusted and the dynamic response of the platform favorably members called tendons. By adjusting the tension in the tendons the draft of the hull can be adjusted and the dynamic response of the platform favorably modified (American Petroleum Institute 1987; Demirbilek 1989). However, TLP hull designs also modify the near wave field, causing both the amplification of wave run-up and forces on the hull, and the waves passing beneath the deck, so that wave impacts on the deck are more likely to occur (Benon and Harding 1989; Banon, Cornell and Harding 1991; Niedzwecki and Huston 1992). Spar platforms are large diameter deep draft which are moored or tethered to the seafloor (Glanville, Paulling and Halkyard 1991). Their large circular cylindrical outer hull presents a simple geometry to the incident wave and current fields. The hull which is moored to the seafloor is designed to support the deck and super structure. Oil storage can also be easily incorporated into the hull design. The hull contains a large central moonpool in which neutrally buoyant riser are located. Like TLPs, the spar platforms also significantly modify the incident wave field and introduce other uncertainties about the water column behavior in the moonpool and hull riser interaction for environment conditions which cause large pitching motions of the spar hull.