308 T. H. Havelock 
SUMMARY 
The wave resistance of a ship in still water can be calculated to a certain 
degree of approximation after making various assumptions. Similar 
calculations are now made for a ship among free surface waves of small 
height; the additional resistance, which may be negative, is considered as, 
to a similar degree of approximation, the horizontal resultant of the 
additional pressures due to the free surface waves. 
The cases considered are (i) when the waves are stationary relative to the 
model, free transverse waves moving at the same speed, and also the case 
of a model on the waves left by another model in advance and moving at the 
same speed, (ii) a model, not free to pitch, in transverse waves moving with 
the speed appropriate to their wave-length. 
It is shown that the additional horizontal forces may be of the same order 
as the wave resistance in still water even when the ratio of wave-height to 
wave-length has only a moderate value. 
The various cases are discussed in relation to available experimental 
results. 
REFERENCES 
Barrillon, E. G. 1926 C.R. Acad. Sci., Paris, 182, 46-8. 
Havelock, T. H. 1936 Proc. Roy. Soc. A, 155, 460-71. 
Kent, J. L. 1922 Trans. Instn. Nav. Archit., Lond. 64, 63-84. 
Wigley, W. C.8. 1934 Proc. Roy. Soc. A, 144, 144-59. 
Reprinted from ‘Proceedings of the Royal Society of London’ 
Series A No. 906 vol. 161 pp. 299-308 August 1937 
PRINTED IN GREAT BRITAIN BY W. LEWIS, M.A., AT THE CAMBRIDGE UNIVERSITY PRESS 
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