Drive Mechanism 



The drive mechanism was powered by a 5-hp, d-c electric motor with a gear reduction 

 assembly that provided a towing speed range of to 20 ft/sec. The system was controlled 

 by a feedback-type power supply which maintained the motor speed within 0.5 percent of the 

 desired setting. The motor was stopped by utilizing regenerative braking. A current limit 

 adjustment switch allowed the starting and stopping acceleration to be preset to any desired 

 value. A traveling-nut-type limit switch assembly, geared to the drive mechanism, provided 

 automatic stopping of the model at any preselected point in the test run. 



The drive mechanism and control console were mounted over the water on a platform 

 resting on the beach at the end of the basin; see Figure 5. This arrangement allowed the 

 operator to visually monitor the drive assembly during testing to ensure that everything was 

 operating smoothly. Part of the platform was enclosed in a wire mesh cage to protect the 

 operator in the event of cable breakage. 



WAVE HEIGHT PROBES 



Three types of wave height probes were used during the course of this investigation: 

 capacitance, resistance, and sonic. Only the sonic type was completely satisfactory. The 

 other two probes penetrated the water surface and their response was affected by surface 

 contamination and by surface tension. At the time of Ralston's experiments, only the 

 capacitance-type probe was available.^ Both Livingston and the author used sonic-type 

 probes which were developed at the St. Anthony Falls Hydraulics Laboratory. 9 Since these 

 probes had to be widely spaced to avoid electrical interference, only two could be used in 

 the experimental setup. In an attempt to increase the number of wave measurements which 

 could be made per run, additional data were obtained with two resistance-type wave probes 

 recently developed at the Model Basin. These probes proved to be difficult to balance, were 

 nonlinear, and were subject to contamination. In the end, all the reported data were obtained 

 with the sonic probes. 



RECORDING EQUIPMENT 



Analog outputs from the three types of wave height probes were recorded with a Series 

 350 Sanborn Recorder. A carrier amplifier system was used with the capacitance probes and 

 a d-c coupling amplifier with the resistance probes. The sonic probes had their own built-in 

 amplifier system. 



In the tests with the 4.5-ft Rankine ovoid, the data were also recorded on DIDAS, a 

 multichannel digital acquisition system. 10 These results were not useful for several reasons: 



