Slipways. In a slipway the vessel is built on a plateau somewhat 
above the high water mark. Upon completion of construction, the hull 
is slid down rails which continue under water. Slipways are oriented 
so the longest axis of the hull is perpendicular to the water's edge; 
in this way, valuable waterfront space is conserved. A variation of 
the slipway is the ''side-launch" type of facility, in which the hull 
is built parallel to the water's edge. 
The slipway suffers from the same limitations as a drydock with 
respect to the maximum outside dimensions permitted for a module. On 
the positive side, such a facility appears to be suited as a dry assembly 
point for long sections composed of prefabricated elements -- in particu- 
lar the cylindrical buoyancy chambers of the semi-submerisble platform. 
At Sea. A fourth possibility for a construction site is the ocean 
itself. For some processes, such as the slip form process (discussed 
later in the text), this is a necessity. For others, the possibilities 
of using the ocean as a work site need further careful study. Particu- 
larly advantageous is the unlimited space and the possibility of harness- 
ing tremendous buoyant forces for supporting heavy loads. 
Concrete Construction Practice 
In general, the MOBS platforms under study entail nothing unusual 
in the way of concrete construction practices. The various types of 
concrete fabrication, such as cast-in-place and precast, have been 
practiced in enough different situations and projects that all but the 
most unlikely problems have been encountered and solved. Trial-and- 
error experience alone has improved the practices and techniques of 
concrete measuring, mixing, handling, transporting, and placing to the 
stage where these operations are essentially routine. Initially, then, 
it is justified in assuming that everything through the placing of 
concrete is virtually independent of the type of construction site; and, 
further, there appears to be no unsolvable problems posed by any of 
those sites previously discussed or reasonably imagined. 
Cast-in-Place Construction. Cast-in-place construction is by far 
the most common approach to building a large concrete structure. The 
basic steps in the procedure include (1) installation of the forms, (2) 
mixing and placing of the concrete, (3) allowing the concrete to cure, 
and (4) removal of the forms. The great bulk of the buildings, 
irrigation channels, dams and similar structures are built in this manner. 
A "cast-in-place'’ MOBS platform or module would be built the same way, 
resulting in the same kind of monolithic structure. 
It is interesting to note that prestressing reinforcement can be 
incorporated into the design of cast-in-place concrete structures. 
Usually post-tensioning is used. All of the advantages of prestressing 
are achieved yet the great dead-load weights of comparable precast units 
are avoided. Ordinary forms and pouring methods are used. The technique 
has been used for all types of structures, including multi-span bridges. 
Dina 
