The elevated platform could be designed so that damaged legs could 
be removed without recourse to dry-docking. Pumps could handle minor 
leaks which might develop from time-to-time, while water-tight compart- 
ments would isolate flooding due to localized failure in a leg. 
Disadvantages. The principal disadvantage of an elevated platform 
is its inherent lack of static stability. A positive restoring moment 
can be assured only if enough ballast is added at the base of the legs 
(or if the length and breadth of the platform is increased, thereby 
increasing the water plane restoring moment). Depending on the plat- 
form size and the weight distribution of the structural and buoyant 
elements, the ballast can assume an appreciable percentage of the total 
weight. 
Compared with the more conventional barge configurations, additional 
disadvantages of the elevated platform include (1) restriction to sites 
having a water depth greater than 300-400 feet because of the platform's 
large draft, and (2) high towing drag. 
Candidate Leg Configurations. Figure 3.2 depicts five candidate 
leg configurations for a MOBS elevated platform. The simple geometry 
of the constant diameter circular cylindrical leg (a) lends itself to 
a variety of construction techniques including, for example, slip form 
casting and post tensioning of precast cylindrical segments. Cylinders 
could be capped with hemispherical end sections or left uncapped, the 
buoyancy of the latter would be adjusted by the addition or removal of 
compressed air. It has even been proposed that cylindrical legs be 
attached to deck sections by use of a gimbaled joint. Supposedly, this 
arrangement will result in, among other things, an elimination of moment 
transfer between the deck and the legs. 
Legs (b) through (e) are typical examples of "bulbous" configurations. 
These legs are characterized by the following salient features (1) a 
low water plane area, which is desirable for minimizing the platform 
dynamic response, and (2) a bulbous shape which results in increased 
damping and induced added-mass, hence, a reduced platform response. 
When used as buoyant support in a modestly dimensioned platform, 
say 300 x 300 feet in plan, any of the legs depicted in Figure 3.2 will 
require considerable ballasting if static stability is to be insured. 
Ballast in the form of dense concrete (addition of scap steel to the 
ballast mix), sand, scap iron or water could be used. 
Barge Platforms 
Advantages. Large concrete floating platforms have several inherent 
attributes which commend them for consideration in the MOBS program. 
It is apparent, for example, that there is a long and successful record 
established in the construction of ocean going concrete barges, ships 
and dry-docks.” A 300 x 300-foot or even a 400 x 1200-foot barge plat- 
form is certainly not beyond today's state-of-the-art in floating 
concrete structures. 
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Seewbaritwe 2. 
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