Analysis Used in Submerged Body Research 447 
Froude numbers. It would also seem that the technique could be extended to cover non- 
linearities if a different sort of recording technique were used. 
J. P. Breslin (Davidson Laboratory, Stevens Institute of Technology) 
I have a few questions I would like to put to the author and the first one is the question 
as to what the David Taylor Model Basin does about strut interference on the planar motion 
experiments. 
The Davidson Laboratory has been operating a rotating arm now for about 16 years and 
has been greatly interested in refining and improving the techniques, particularly for the in- 
vestigation of interferences, of coupling effects, and of nonlinear behavior of submarines and 
bodies of revolution with a mind to exploring the behavior of such vessels in radical maneu- 
vers. In this regard, it is rather interesting that in the model regime the Navy has been able 
to get along without very much information in this area of large course deviations for this 
long period of time. We look forward with great interest to the developments which will 
come from the David Taylor rotating arm, not only for the comparisons for which Mr. Tupper 
asked, but also for the predictions of nonlinear coefficients which are necessary for modern- 
day treatment of evasive and radical maneuvers. 
My second point has to do with the assertion that in regard to accuracy one ought to 
look somewhat askance at rotating arm methods for determining static derivatives. The 
Davidson Laboratory and the Model Basin have had a number of discussions on this matter 
and as a matter of fact the Model Basin has supported us in the very recent past in an ex- 
perimental investigation in which we conducted experiments in the straight tank to measure 
static derivatives and repeated the experiments on the rotating arm, interpolating or extrap- 
olating, depending upon how you interpret the procedure to obtain the derivatives at infinite 
radius. I am happy to say that these experiments,* as well as several that have been made 
in the past, always give very close agreement. Of course, general statements of a sweeping 
nature are all subject to exceptions and perhaps the class of bodies with very small damping 
is one in which close scrutiny should be made of the difference between the techniques. 
Finally, I would like to call the attention of the participants to the great usefulness of 
the small model in such explorations to map out the gross effects of shape and control sur- 
face location so that modern concepts of optimizing maneuverability and controllability can 
be more readily achieved. The David Taylor Model Basin has certainly done an exceptional 
job in developing equipment which is suitable for proof testing of designs and this is a very 
important aspect of their part in the naval establishment, but it is urged that the use of the 
rotating arm at the Davidson Laboratory and other small facilities be continued for interest- 
ing exploratory research. 
R. Brard (Bassin d’Essais des Carenes, Paris) 
I would like to say how we appreciate the work done by the David Taylor Model Basin 
in order to study the maneuverability of the submarines and I would too address warm con- 
gratulations to the staff, and particularly Mr. Goodman, for their beautiful results, specially 
those concerning the maneuvering of the submarine under the polar ice cap. 
*S. Tsakonas, “Effect of Appendage and Hull Form on Hydrodynamic Coefficients of Surface Ships,” 
Davidson Laboratory Report 740, July 1959 
