Floating production systems are essentially semisubmersible drilling rigs, except that they contain petroleum production equipment, as well as drilling equipment. Ships can also be used as floating production systems. The platforms can be kept in place through large, heavy anchors, or through the dynamic positioning system used by drillships. With a floating production system, once the drilling has been completed, the wellhead is actually attached to the seafloor, instead of up on the platform. The extracted petroleum is transported via risers from this wellhead to the production facilities on the semisubmersible platform. These production systems can operate in water depths of up to 6,000 feet. Choosing the right FPS depends on the water depth, hull motions, and the type of riser system desired. The riser system and the motions of the FPS hull are key. For tensioned risers, the wellhead has to be accessible from directly below the FPS. Once below the mudline, wells can divert in different directions to access particular reservoirs, which could be several miles away. However, if the reservoir is fragmented, spread over a large area, or has tiebacks, a steel catenary riser (SCR) is used. Basically, an SCR is a pipeline that’s been picked up off the floor and hung off the FPS. The riser is the section of the pipeline from the mudline up to the FPS. To use top tensioned risers (dry trees) or SCRs, a spar or tension leg platform (TLP) is traditionally used because of their small in-place motions. A spar has a deep draft of 550 ft, and a TLP’s motions are constrained by tendons designed to withstand tensions induced by wave forces. A conventional semisubmersible is not designed to support dry tree risers. Its shallow draft of 60-80 ft creates motions too large to use top tension risers or SCRs. TLPs typically work in water depths less than 5,000 ft because of their tendon design. Therefore, from 5,000-10,000 ft, the only top tension riser choice is a spar. The one disadvantage to a spar is its delivery method. It has to be towed out to its final location on its side, up right, and placed on its moorings. The topsides then have to be lifted by modules and commissioning is done offshore, which is expensive and risky. Topsides for TLPs and semisubmersibles are lifted quayside, and the entire FPS is towed to its location and installed. Furthermore, a semisubmersible and TLP have larger deck areas than a spar. A spar is limited to its diameter, so operators end up stacking the decks. A spar could have three decks as opposed to one or two on a semisubmersible or TLP. Ideally one would like to have the functionality of a semisubmersible, but the motions of a spar.