duct for removal of 
spoil as slurry 
—, < P 
Pe— side or end cutting 
auger with slurry 
removal of spoil 
Figure 48. Concept of mobile seafloor excavator. 
nonretrievable 
concrete clump 
| ; seafloor : a 
vst | Sel anus 
i 
Figure 49. Concept of a fixed seafloor excavator. 
A total of eight concepts were identified in the early phase of the 
work; these were reduced to three in an early trade-off analysis. The three 
distinct concepts (Figure 52) are: (1) a frame which would require towing 
and sinking at the work site and which would be capable of very precise prov- 
ing over a limited area; (2) a rotary machine capable of similarly close-tolerance 
excavation, but having the added inconvenience of requiring a drilled-in pile 
and a specialized drilling support ship, of which there is only one; and (3) the 
concept selected for preliminary design and detailed analysis (right, Figure 52). 
62 
