of the geometry of the hull and shafting of the configuration under eval- 
uation, it was not feasible to achieve both these criteria with an up- 
stream drive system from inside the model hull. Criteria 1 and 2 con- 
trolled the minimum allowable beam and draft of the downstream body and 
the maximum allowable clearance from the bow of the downstream body to the 
propeller. Although the downstream body may exert some influence on the 
flow into the propeller, that location was considered necessary in order 
to meet these measuring criteria. The influence of the downstream body 
on the flow into the propeller is discussed in the section on experimental 
results. 
The drive and mounting system was basically the same as that used 
in the DINSRDC BASS dynamometer which has been described by Beaadedeaa 
Utilized from this dynamometer were the propeller (tail) shaft, drive 
shaft with flywheel, belt-type (quiet) transmission, and sliprings. 
Power to rotate the propeller was supplied by a d-c permanent-magnet 
servomotor capable of delivering up to 33 foot-pounds (45 N-m) of torque. 
The electrical power to this motor was delivered through a precision 
solid-state motor controller so that the shaft revolution rate could be 
controlled very accurately and held over the wide range of propeller 
torque loadings required for some of the experimental conditions. Mounted 
on the propeller shaft was a digital encoder that generated electrical 
pulses as a function of shaft angular position. Two types of pulses were 
generated: a single pulse per revolution and a multipulse per revolution 
(90 equally spaced pulses for the current experiment). The single pulse 
was syncronized with the reference line of the instrumented propeller 
blade. The pulses generated by this encoder are accurate to within 0.01 
degree. 
The downstream body which housed the drive system was basically that 
used by eibag but modified to allow deeper submergence and an inclined 
shaft angle. Both the body housing (the drive system was soft mounted to 
this body) and the model hull were rigidly attached to a pitch-heave 
or less, J.H., "Static and Dynamic Calibration of Propeller Model 
Fluctuating Force Balances," David Taylor Model Basin Report 2350 (March 
1967); also Technologia Naval, Vol. 1, pp 48-74 (January 1968). 
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