446 Alex Goodman 
DISCUSSION 
H. N. Abramson (Southwest Research Institute, San Antonio) 
Submerged body technology shows two interesting trends; one is toward increasing fine- 
ness and the other is toward higher speed. These two together tend to introduce a new im- 
portant factor and this is the elasticity of the structure. In short, hydroelastic considera- 
tions may become important for stability and control investigations of submerged bodies. I 
would very much like to have the author’s comments on what considerations he and his col- 
leagues have given to introducing hydroelastic effects into their theoretical and experimental 
studies. 
E. C. Tupper (Admiralty Experiment Works) 
The author mentioned in his paper the question of certain standards by which the per- 
formance of the submarine could be judged. I would like the author if he will, to state what 
these standards are in both the vertical and the horizontal plane. Only by studying in a 
computer, say, the way in which the performance of the submarine: varies as regards these 
standards, can one judge the importance of various hydrodynamic derivatives. For instance, 
the author mentioned that we have what are commonly called the static, rotary, and accelera- 
tion derivatives. We feel, at the Admiralty Experiment Works, that the acceleration deriva- 
tives are not critical. There are basically four for the simple equations of motion in the ver- 
tical plane and we feel that two of these can be ignored and the other two can be calculated 
with sufficient accuracy and therefore do not need to be measured. 
We have not studied the horizontal plane problem completely, but we feel that the most 
important point here is the nonlinearity introduced by the very large reductions in speed which 
can occur when maneuvering in the horizontal plane. I would like to make a plea, therefore, 
for some description of the standards which the author considers to be important. 
It would be very interesting if the author could give us any information on comparisons 
between results with the oscillator technique which he has described and other methods of 
test, in particular the comparison with the rotary derivatives between the oscillator and ro- 
tating arm methods of testing. 
S. T. Mathews (National Research Council, Ottawa) 
I think we should congratulate Mr. Goodman and his colleagues at the David Taylor 
Model Basin for developing what I consider the most powerful method of considering this 
submarine stability and control problem, experimentally anyway. Surely these experimental 
results are most useful or even essential before we further develop the theoretical methods. 
I have a few points of detail. I would like to ask Mr. Goodman if the carrying out of static 
moment and force tests is not superfluous, because the same results are obtained by the 
oscillating heaving tests. I would be glad to have any comments he has on how the results 
obtained by the two methods compare. Mr. Tupper took one of my points. I was going to ask 
specifically if we could have any comparisons between results obtained for the rotary static 
moment and force derivations from the oscillating mechanism as compared with a rotating arm. 
It seems to me that no mention has been made of surface models; for linear seaworthiness 
considerations one could obtain much useful data using the oscillating mechanism technique, 
in pitch and heave, and also we could get results in yaw, I would think, certainly at low 
