Lang 



REPLY TO DISCUSSION 



Thomas G. Lang 



Naval Undersea Research and Development Center 

 San Diego, California, U.S.A. 



In answer to the first comment, we have not seen in our ex- 

 periments any of the head sea resonance problems that Dr. Salvesen 

 mentioned. As you saw in the motion picture, the S model has 

 extremely high damping when under way, in both roll and pitch. This 

 large damping is provided largely by the canard fins at the front, and 

 the stabilizing fins at the back. It is probable that the differences 

 from Dr. Salvesen' s results are due to differences in design form 

 from the S model. We have found relatively good comparisons bet- 

 ween experiment and theory ; in general, the experimental results 

 tended to show less motion than theory would predict, especially in 

 the following sea case. 



As far as automatic control is concerned, all of the tests 

 you saw in the motion picture were without automatic control, so it is 

 seen that the craft can operate effectively without automatic control. 



In the case of following seas there is no motion problem 

 until the waves reach a certain height. When not using automatic con- 

 trol, large craft motion in the very highest waves in a following seas 

 can be alleviated by slowing down approximately the wave speed, or 

 less. 



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