The precise excavation foreseen as necessary for ocean-floor sites 
will be largely accomplished by a machine that will function similarly to a 
numerically controlled milling machine (Figure 47). However, instead of 
moving the workpiece below the mill with respect to a stationary cutter, it 
will be necessary to move the milling head with respect to a movable platform 
(Figure 48),* or with respect to a fixed clump (Figure 49). Where preparation 
of the immediate area is needed for installation of a prefabricated structure 
or other assembly, the massive clump would be lowered with the earth-milling 
equipment in place. Upon completion of the excavation phase, the machinery 
would be detached and raised to the surface, leaving a precisely formed area 
to accept the permanent installation. 
In conventional metal milling (Figure 47) cuttings are flushed away 
or removed by hand. Soil or rock cuttings, on the other hand, will be immersed 
in water and relatively finely divided. It remains only to cut them in such a 
way that they can be sucked into the rapidly moving fluid stream and pumped 
either into a fast moving current or to a site away from the operation, where 
they will form a harmless sediment. Use of water for spoil removal is the big 
plus in underwater operations. 
At least two evident mechanisms for traversing the cutting head or 
mill over the work area are available (Figure 50a and 50b). In the arrangement 
of Figure 50a, the cutter would be traversed over an area ahead of the support- 
ing barge by movement of tubular ways. A second set of ways would traverse 
it at right angles, and the vertical movement would be accomplished through 
a vertically moving column bearing the mill, pump and hose as necessary. This 
would be essentially duplicating the motion of the ways and milling head of 
a vertical mill (Figure 47). From a control standpoint, it would be desirable 
to use this arrangement. The standard programs and control techniques for 
numerically controlled machines could be used with little modification with 
such a machine in conjunction with three-dimensional rectangular coordinates. 
Development of suitable controls for the type of machine illustrated 
in Figure 50b, on the other hand, would probably require greater effort, as 
instructions would have to be translated from the normal engineering rectan- 
gular coordinates to a combination of polar coordinates in the horizontal plane 
and a linear coordinate in the vertical, resulting in a combination which might 
be called cylindrical coordinates. Mathematically, this is not difficult, but the 
change does introduce one additional step in instructing the machine. The 
resulting machine would be mechanically far simpler than that diagramed in 
* See also Figure 46 and related text. 
59 
