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2 SEMI-SUBMERSIBLE PLATFORMS AND
TENSION LEG PLATFORMS
In addition to the mono hull, three floating structure
designs ─ Semisubmersible (Semi), Truss Spar and Tension leg
Platform (TLP), ─ have been successfully developed for use as
floating production systems (FPS) over the past several decades.
Each of these floater designs has evolved along with subsea and
riser technology to meet new field development challenges related
to increased water depth, drilling, and reservoir operating
pressures and temperatures. Design improvements continue to be
made as new developments in deepwater technology are
incorporated into the basic designs.
The functional requirements for floating structures can be
generalized as:
Drilling facilities
o Number, type and location of drilling rig
Production facilities
o Weight, area and center of gravity
Drilling / production risers
o Number and arrangement
Well systems
o Number of wells, completion and workover methods,
minimum well spacing and well bay location
Hull compartmentalization
o Damage stability considerations
Air gap requirements
o New metocean criteria
As illustrated in the following figure 2.1, the relative hull
responses of the three designs vary considerably. In all cases the
objective is to minimize the response to the environment. Efficient
design of floating structures is predicated on functionality and
performance – it should be capable of supporting all the necessary
equipment for production and related tasks while meeting all
performance criteria. The structure should provide sufficient space
and robustness to fulfill its intended purpose; also, the floating
structure should be built at a minimum of cost, which is governed
mainly by the hull steel weight. Hull weight estimates are based on
global sizing which is determined by the naval architectural and
structural design. Global sizing is a key engineering design process
in both the concept selection stage and design phase of a floating
structure. The sizing of a moored floating structure considers

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