to twice the draft of the ship, and must be snubbed quickly by use of 

 the windlass brake; and must not touch bottom. The ship must be dead 

 in the water for this test, with a minimum of rotating equipment in 

 operation. Care should be taken not to exceed the anchor windlass 

 manufacturer's recommendations for free drop. Data should be taken 

 continuously from the moment the anchor is released until vibration 

 can no longer be detected. 



ANALYSIS AND REPORTING OF DATA 



vibration. 



Analysis shall provide the following information for all 



(1) Maximum overall values of amplitude. 



(2) Maximum amplitude of first -order (shaft -frequency) 



(3) Maximum amplitude of blade -frequency vibration. 



(4) Maximum amplitude at each detectable harmonic of 

 blade frequency. 



(5) Maximum amplitude at hull resonant frequencies. 



Maximum amplitude is defined as the average of the high- 

 est 10% of all amplitudes at a given frequency which are present in a 

 vibration record. For reducing oscillograph data, the procedures 

 given in "Waveform Analysis, " by R. G. Manley (John Wiley & Sons, 

 Inc., 1946) are recommended. 



b. Data reported shall include the following: 



(1) A tabulation of all results, following the outline of 

 Table 1, for both Free Route (straight course) and Maneuvering Runs. 



(2) Separate curves of single -amplitude of displacement 

 vs. RPM, for the following Free Route measurements: 



a) Vertical hull vibration. 



b) Athwartship hull vibration. 



c) Vertical vibration of thrust bearing foundation. 



d) Athwartship vibration of thrust bearing foundation. 



27 



