Elevated Platform 
The following design/performance criteria are considered to be 
important for all elevated platform configurations: 
Length of legs Drag under tow 
Spacing of legs Total weight and distribution 
Shape of legs of weight 
Static stability Freeboard 
Dynamic stability Station keeping 
Length of Legs. The length of the platform legs is an important 
consideration for several reasons. For example, lengthening circular, 
constant diameter legs results in an increase in the useable freeboard, 
an increase in the total mass of the platform and adversely affects the 
platform's static stability. If the legs are too long, the resulting 
draft will inhibit operations in shallow water, and the legs may be 
difficult to form, transport and attach to the platform. Obviously, 
by fixing the deck weight and freeboard and then lengthening the legs 
will result in reducing the number of legs required (i. e., increase 
the spacing) and/or reduce the required leg diameter (reduce the water 
plane area). 
Spacing of Legs. This parameter is closely allied to the preceeding 
one. The relationship is especially obvious for platforms with uniform 
leg spacing in both deck plan dimensions. If, as before, the deck weight 
and freeboard are fixed, then increasing the spacing, i. e., reducing 
the total number of legs, must result in either longer legs or larger 
diameter legs (or both) in order to maintain buoyancy. The opposite is 
true if the spacing is decreased. 
It may be desirable to reduce the total number of legs for several 
reasons. With fewer legs there will be less handling required during 
construction, although the legs will be correspondingly larger). Also 
it may be considered very desirable to include a center-well in some 
MOBS platforms for the purpose of raising and lowering heavy, outsized 
loads, e. g., acoustic arrays; and it will be necessary to insure that 
buoyant support members do not interfere with operations through the 
centerwell. If the leg spacing is large enough to allow, say, a fifty 
foot clearance between adjacent legs, it may be unnecessary to leave 
gaps in the spacing. A plausible argument can be made for including a 
lift-dock in MOBS and consideration must be given to the effect that 
this feature would have on leg spacing. 
If the deck is envisioned as a single slab or a multi-level structure 
resting upon the vertical legs for support, then it is apparent that a 
large leg spacing will result in greater loading in the deck spans. 
Thus, increasing the leg spacing has the effect of requiring an increase 
in the deck thickness. The resulting increase in deck weight can only 
