and 187.5 feet long (recorded at 1-7/8 ips) becomes a loop 5.86 feet 

 long which takes 2.34 seconds (at 30 ips) to make one complete trip 

 through the loop recorder. 



It will be recalled that the probable frequency range for seakeeping 

 data is 15.4 to 1540 cps at a speed-up of 512. Commercial filters from 

 2 to 20 cps are well suited for this range in terms of giving adequate 

 resolution of the spectral density and have) as well, a fairly rectangular 

 shape, which is desirable. 



Tests in irregular waves in model tanks will often contain frequencies 

 which are sufficiently high (depending on speed and nelative heading of 

 ship model) to obviate the necessity for re-recording. In such cases, the 

 recorded signal is bound into a loop directly and played into the analyzer 

 at 60 ips, providing a direct speed-up of 32. 



3. DATA ANALYSIS 



The data reduction portion of the SEADAC consists of two conventional 

 linear- frequency , constant bandwidth wave analyzers specially modified 

 to be driven by one stabilized local oscillator. One analyzer has four 

 filters (2, 5, 10, and 20 cps) and the other analyzer has two filters 

 (2 and 5 cps) . 



The oscillator is capable of sweeping three ranges: 



1. 0-250 cps 



2. 0-2500 cps 



3. 0-25,000 cps 



8 



