within the recommended mobile concept. While the study showed a marked 
advantage in reliability and cost, and only a slight disadvantage in weight in 
the electro-hydraulic over the all-electric system, Northrop’s recommendation 
was still for the electric system. The relative merits of these and other combi- 
nations need further intensive study before final judgment can be made. 
A considerable body of experience and test data on various components 
is being accumulated by the Navy Laboratories, and it will become increasingly 
desirable that this be collated and inspected as each piece of equipment goes 
into the final design stage. It is proposed that collation of information and 
the intensive and realistic assessments of the type done by Northrop (1970) 
be the major effort for the near future. 
This preliminary examination of the problem indicates that conversion 
of power transmitted electrically, mechanically, or pneumatically from the 
surface to hydraulic power will be the preferred and most reliable approach. 
When practicable, all components of the Seafloor Excavator and Large Hole 
Drilling System will be operated through hydraulic power and controls. To 
avoid sealing problems, the preferred hydraulic fluid would be filtered seawater, 
but for the near future small-scale subsystem experiments will be conducted 
with two-hose closed hydraulic systems, pending development of suitable sea- 
water motors. 
Future Plans 
The objectives of the current development effort are high-pressure 
pumps and motors with the same advantage as those using conventional 
hydraulic fluids, but capable of using pressurized seawater as the working 
fluid. The initial developmental effort of small, compact units suitable for 
use In conjunction with divers hand-held tools is in progress under a develop- 
ment work unit funded at NCEL by the Supervisor of Salvage, U.S. Navy. 
Further development will be carried on after FY 70 in the Navy's Deep 
Ocean Technology Program, especially in the development of drilling and 
excavating machines usable on the deep ocean bottom. The pertinent DOT 
work units are: Rotary Cutter and Hydraulic Earth Moving Equipment 
(Work Unit No. 64-016) and Basic Chassis for Bottom Systems Support of 
Drilling Equipment (Work Unit No. 64-017). 
CHASSIS FOR SUPPORT AND MOBILITY OF EQUIPMENT 
There are three basic technical problems in developing a useful 
underwater construction chassis. First, large equipment weights must be 
supported at the soil—water interface. Because many bottom materials are 
33 
