Vertical Legs for Elevated and Semi-Submersible Platforms. The 
vertical legs were designed to support the deck dead and live loads and 
to resist the imposed hydrostatic and hydrodynamic pressure. Adequate 
lateral support between legs to prevent buckling was assumed. 
Horizontal Buoyant Members for Semi-Submersible Platforms. It was 
assumed that the critical loading condition for the horizontal cylinders 
is the surrounding hydrostatic pressure. The design of the connection 
between these members and the vertical legs was not attempted. 
Barge Platforms. For all three sizes of the barge platform, the 
pontoons were considered to be spanned by a solid, two-way deck slab. 
Two interior deck levels were provided in each for internal storage of 
aircraft, equipment and personnel. 
Hyddrodynamic Design - Assumptions and Procedure 
Static Stability. All of the platforms summarized have at least 
neutral static stability* An acceptable standard for static stability 
has not been established for MOBS. More information is needed on the 
type and possible distribution of the live load and the effect of pitch 
and roll on aircraft operations and habitability. A platform which has 
low transverse static stability will inherently have a long natural 
roll period. Thus, a platform with roll period, say on the order of 
100 seconds would be ideal for a floating airbase, but may be so near 
static instability as to be severely limited in its load carrying 
capacity. 
Dynamic Stability. A floating platform has six possible modes of 
motion: linear displacement as heave, surge and sway and angular dis- 
placement as pitch, roll and yaw. For MOBS the most important modes 
will probably be heave, pitch, and roll?* 
An analytical scheme for predicting the elevated platform motion 
in heave was developed and proved to be a useful aide in selecting 
feasibile platform configurations (See Appendix A for details). Al- 
though the equations have been linearalized, i. e., they are applicable 
to small amplitude motion only, the results are worthwhile when properly 
interpreted. 
It is particularly important that the correct values for the damp- 
ing and added-mass coefficients be used if response accuracy is desired 
at resonance. The damping and added-mass are dependent on the motion 
of the platform: on velocity for damping and acceleration for added- 
mass. Since the predicted results are relatively insensitive to a wide 
range of values for these coefficients outside of resonance, where the 
“several, such as the barge platforms and the elevated platforms with 
a deep draft, have considerable positive stability. 
HK 
Pilot tests recently conducted at NCEL of an elevated platform indicate 
that surge may also be important. 
