Drifting Force on a Ship among Waves. 475 
Summary. 
The problem considered is the drifting force on a ship when head-on 
to a regular train of waves. A satisfactory theory would have to include, 
among other factors, the effect of reflexion of the waves by the surface 
of the ship; in the present note this is neglected in order to make 
tentative calculations from another point of view which associates the 
effect directly with the oscillations of the ship. A steady average 
drifting force is obtained depending upon the phase differences between 
the heaving and pitching motions and the periodic forces and couples 
due to the wave motion. An examination is made of experimental 
results and, although available data are not suitable for detailed com- 
parison, it appears that the calculations give drifting forces of the right 
order of magnitude. 
References. 
T. H. Havelock, Proc. Roy. Soc. A, elxi. p. 299 (1937). 
T. H. Havelock, Proc. Roy. Soc. A, clxxv. p. 409 (1940) 
F. Horn, Jahrb. Schiffbau. Ges. xxxvii. p. 153 (1936) 
J. L. Kent, Trans. Inst. Nav. Arch. Ixiv. p. 63 (1922). 
J. L. Kent and R. S. Cutland, Trans. Inst. Engrs. and Shipbrs. Scotland, 
Ixxxiv. p. 212 (1941). 
J. Kreitner, Trans. Inst. Nav. Arch. Ixxxi. p. 203 (1939). 
K. Suyehiro, Trans. Inst. Nav. Arch. Ixvi. p. 60 (1924). 
Y. Watanabe, Trans. Inst. Nav. Arch. lxxx. p. 408 (1938). 
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