For the anchor drop-and-snub test, vertical measurements 

 were made at the Stern and Thrust Bearing Foundation when the star- 

 board anchor was dropped. Data was taken continuously during the 

 anchor drop test while the anchor was repeatedly paid-out and snubbed. 



During the maneuvering runs, data were obtained on the Stern 

 in the vertical direction and at the Thrust Bearing Foundation in the 

 fore and aft direction. During stern operation and crash ahead condi- 

 tion, channel II was switched from fore and aft response at the Thrust 

 Bearing Foundation, to athwartship response of the Stern. 



DATA REDUCTION PROCEDURES 



(Note: If the standard instrument package available from the Maritime 

 Administration is used, a standard write-up will be provided for this 

 section. ) 



The methods employed in reducing the test data is of equal 

 importance to the proper choice of instruments, adequate calibration 

 and suitable test procedure. Since the vibration present in the hull of 

 a ship does not remain at a constant level, but rather increases and 

 decreases, it is most important that a standard technique be employed 

 in the evaluation of data for comparative purposes. 



In this program, the maximum value is taken as the average of 

 the highest 10% of all amplitudes at a given frequency. Thus, only those 

 sections of the oscillograph records which show the largest amplitudes 

 need be reduced. 



The measurement of the amplitudes on the records themselves 

 is considered important. Since the records are not normally evaluated 

 by a formal Fourier Analysis, nor does the evaluation warrant it, it is 

 nevertheless important that a common and acceptable procedure be em- 

 ployed. A sine wave of the predominant frequency should be drawn 

 through the complex wave. Thus, the actual vibration record is replaced 

 by one of mean amplitude. This is particularly apparent in the electronic 

 data which has adequate response and amplification to record most fre- 

 quencies present. As a practical demonstration of this process, see 

 Manley, R.G., " Waveform Analysis, " John Wiley & Sons, Inc., 1946. 



46 



