platform velocities and acceleration are small, any "reasonable" 
choice of coefficient will suffice for predicting the response in that 
frequency domain. This is fortunate since it is difficult to predict 
the damping and added-mass effects by analytical means. Recourse is 
usually made to experimentation for the answer. 
Results 
Size and Weight. Preliminary design specifications for five types 
of MOBS platforms are presented in Table 3.2. The platform types 
summarized are: 
- Semi-submersible platform with single level deck. 
Semi-submersible platform with multi-level deck. 
Elevated platform with single level deck. 
Elevated platform with multi-level deck. 
Barge platform. 
OPWN eR 
0 6G O16 
The tabulations for the elevated platform and the semi-submersible 
platform are given for both single and multiple decks. These values 
represent the extremes, since in all probability the optimized designs 
for specific missions will have combinations of single and multiple 
decks; the weights of such platforms will lie between these extremes. 
The barge-hull platform has interior decks; the single deck did not 
appear practical for structural reasons. Thus, only one tabluation for 
the barge is given. 
It is apparent from Table 3.2 that considerable savings in concrete 
are possible with the barge platform. This can be seen clearly in 
Figure 3.8 which compares the weight of the multi-level deck, elevated 
and semi-submersible platforms with the barge platform. The platforms 
each have the same plan dimensions, i. e., 300 x 300—feet, and support 
the same live load. The weight advantage, and material savings, of the 
barge configuration is reflected also in the estimates for the 400 x 
1200-foot and 1000 x 4000-foot size platforms. 
Figure 3.9 illustrates the relative size of the three MOBS base 
concepts while the freeboard and plan dimensions are identical for 
each platform. The principal difference lies in the draft for each 
candidate, the elevated platform having a loaded draft more than five 
times that of the barge. 
Dynamic Response. The natural heave periods for three selected 
300 x 300 platforms are presented in Table 3.3. The estimates for the 
elevated and semi-submersible platforms were determined from the fol- 
lowing expression: neue 
where T. is the natural period in heave, k is the restoring force per 
foot of submergence and M is the total mass of the platform (including 
the mass of the live load and the added-mass). 
