A Vortex Theory for the Maneuvering Ship 



0,05 



PURELY PITCHING MOTION 

 bappAND|^(X2+Xa^J 



- + 



Figure IV 



These planes were located near the stern (at about 0, 12 the total length of 

 the model). 



The sheets show that the variations of some apparent coefficients may be 

 great, particularly those of a^^^. 



These variations have been explained not only by the influence of the wake 

 on the body, but also by its influence on the planes. It was thought that 

 <0(O) < 1 , and, consequently, that the wake acts in opposite directions on the 

 body and on the planes. 



At the time, we considered as certain that and 0' were identical; and 

 found that the lift acts through a point behind the middle section in the case 

 when Lq/u = 0, and also in the case when w/u = 0. 



Later on, other tests were carried out by using our Planar Motions Mech- 

 anism. They showed that it is possible that < 0, and consequently, that the 

 wake already acts on the body itself in such a way that a^pp, without planes, is 

 increasing function of wL/u. In this case, the total variation of a^ with planes 



may be very large; the limit seems to be obtained for 

 about three times higher than the value for wL/u =0. 



oL/u = 10 or 12, and to be 



In spite of these new experiments, we do not deem to be able presently to 

 formulate general conclusions about the effects of the wake on the body itself. 

 In return, we think that the effect of the wake on rudders or stern planes is 

 really of a great importance. A closer analysis of this phenomena would re- 

 quire the study of the blockage effect, of the waves generated by the moving 

 body and also of the influence on the lift of the Reynold's number which is 

 already great during steady forced motions. 



221-249 O - 66 - 58 



897 



