Semi-Submersibie Platform 
Most of the design/performance parameters of interest for the 
elevated platform apply equally as well to the semi-submersible concept. 
Thus, the reader is referred to the previous discussion on the elevated 
platform. 
Especially noteworthy for the semi-submersible is the significant 
amount of added-mass induced by oscillation of the submerged horizontal 
pontoons. Increasing the girth of these buoyant elements results in 
an increase in the added-mass which is desirable from the standpoint 
of platform dynamic response. 
Barge Platform 
Optimization of a barge platform is dependent on the following 
design/performance criteria: 
Configuration of buoyant support 
Static and dynamic stability 
Hydrodynamic drag 
Freeboard 
PWN er 
Type of Buoyant Support. As opposed to elevated and semi-submers- 
ible platforms, barge platforms have a shallow draft. Barge hulls can 
be continuous, extending the width and breadth of the deck, or they can 
assume a catamaran or trimaran configuration, etc. Compared to a full- 
beam hull, the catamaran or trimaran hull offers the advantage of in- 
creased static and dynamic stability. This advantage is offset, however, 
by an increase in the platform draft, the need to account for hydrodynamic 
loads transmitted to the cross structures (Bond, 1970) and the probable 
increase in the total mass of the platform. The latter is due largely 
to the need for structural members to support the deck span between 
pontoons. 
Static and Dynamic Stability. Typically, barge or ship-like float- 
ing structures have adequate longitudinal static stability, and this 
need not be a major concern for larger size MOBS platforms. A small 
MOBS platform, however, will require a check of both transverse and 
longitudinal stability under all loading conditions. Generally, catama- 
ran hulls are noted for their favorable transverse stability, and this 
is one more cogent reason for adopting this configuration for a barge 
type MOBS platform. 
Shallow draft floating platforms, which typically have a relatively 
large water plane area, unquestionably will be more susceptible to 
wave induced motion than comparable elevated and semi-submersible plat- 
forms. Again, compared to the flat bottom hull, the catamaran is a 
better performer, due largely to its greater draft and decreased water 
plane area. 
