semi-consolidated sediments or soft to medium 
hard rocks, a cutter head (normally of the rotating 
hollow bit type) usually is employed. The head is 
mounted on the lower end of the suction pipe to 
break up the ground and direct the flow of solids 
into the suction pipe. 
The suction dredge method is best suited for 
recovery of large quantities of unconsolidated 
material. For example, this technique is used for 
channel maintenance as well as mineral recovery. 
Its water depth capability is up to 200 feet. 
Dredges using a rigid ladder are limited to pro- 
tected waters or fair weather operation. 
Recent improvements in size and capacity of 
hydraulic suction dredges for engineering construc- 
tion work have caused renewed interest in their 
application for offshore mining. Preliminary de- 
signs have been made to recover sea floor nodule 
deposits at depths greater than 4,000 feet by this 
method. At such depths it probably will be 
necessary to establish additional submerged pump- 
ing capacity. Hydraulic dredging will almost cer- 
tainly be applied in deep sea mining. 
2. Deep Ocean Mining 
The mining of deep sea manganese nodules has 
attracted serious evaluation and interest. It has 
been asserted that nodules constitute a renewable 
resource, their estimated renewal rate exceeding 
the present world rate of consumption for the 
elements contained in them (chiefly copper, 
nickel, cobalt, and manganese). 
However, this may not be of practical signifi- 
cance because in the limited areas economic to 
mine, the rate of renewal is not adequate to 
sustain continuous mining. Technology for the 
economic exploitation of deep sea nodules has not 
yet been demonstrated. The problem is not only 
that of economic recovery but also of economi- 
cally separating the elements from the raw nod- 
ules. 
Various design studies have been made on 
nodule recovery. One such method conceives of an 
air lift or suction dredge mounted on a wheeled 
vehicle or sled towed along the ocean floor by a 
flexible pipeline secured to a surface vessel. The 
direction and speed of the mining device would be 
controlled by the heading and speed of the surface 
ship. An underwater acoustic transponder system 
would monitor the position of the mining device 
relative to the bottom mining area. The ore could 
be dredged and piped to the surface for loading 
into ore barges for transportation to shore facili- 
ties. The ore might be concentrated at sea to lessen 
the amount of material that must be transported. 
A similar system designed in Canada recom- 
mends a light-weight medium (such as kerosene 
instead of airlift or suction) to actuate a very high 
velocity upward flow through the conduit, lifting 
the heavy nodules faster than they can sink 
through the stream. 
One of the more sophisticated ocean mining 
approaches is a_ self-propelled bottom mobile 
mining system in which a suction dredge is 
mounted on a bottom mobile crawler or wheeled 
vehicle. The power required for mobility, naviga- 
tion, and dredging is supplied by cable from the 
mining control vessel at the surface. The product 
must be lifted to the surface by supplementary 
equipment. 
Deep ocean mining will require development 
and evaluation of many new types of equipment 
heavily dependent on marine technology advances. 
Examples include: (1) submarine crawlers and 
bottom hovering vehicles to explore for and 
recover deposits, (2) stationary or neutrally buoy- 
ant platforms, (3) drilling rigs on the ocean floor, 
(4) submarine dredges, (5) high capacity, low cost 
vertical transport systems, and (6) high capacity 
equipment for horizontal transfer. 
Typical basic engineering needs of deep ocean 
mining: (1) sufficient power to lift thousands of 
tons of minerals from great depths, (2) ultra-high 
strength, corrosion-resistant hoisting cables, (3) 
long, flexible pipes for deep water that can 
withstand the anticipated bending and shearing 
stresses, and (4) the ability to provide three-phase 
flow through long pipes. Further, very high as- 
cending water velocities probably will be required 
to lift even small manganese nodules, requiring 
larger manganese nodules to be broken into small 
pieces on the sea floor or retrieved differently. 
Other difficulties may be encountered where a 
solid crust of manganese or phosphorite covers the 
sea floor. 
3. Sub-Bottom Mining 
Except for sulfur (Frasch process) and coal and 
iron (tunnels from land) the task of extracting ores 
from rocks beneath the continental shelf is an 
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