T. H. HAVELOCK 
The part of the pressure system which is effective for this purpose 
is first put into a suitable form, and an expression is obtained for the 
moment for a certain type of model whose form is given by an equation 
involving one parameter. This moment is then turned into an equiv- 
alent angle of trim for the ship, using the ordinary righting moment 
as if in still water. Finally, numerical calculations are made for 
three models of this series, with different values of the parameter, 
for which experimental results are available. Curves are given show- 
ing the calculated and measured trim for these three models. 
2. We take the origin O in the undisturbed free surface of the 
water, Ox in the direction of motion, Oz vertically upwards and Oy 
transversely, » being the velocity. If there is a source of strength 
m at the point (h, 0, -f), the velocity potential is given by [2] 
Dah cata lh | © Geka 
| sectead | $$. (1) 
™ 7, 7 k—K, Sec’ 0 + iusecd 
pees i 
with 
r2a(w—hyr+y?(2tf)?s yg? = (eA)? +9? +(2-f)"s 
@ =(x—h) cosé+ysin 0 Ko =g/v’. 
The pressure p, other than the hydrostatic pressure, is given by 
0 
p= pv ee. (2) 
We require the part of the pressure due to the waves trailing aft from 
the source. From (1) and (2), taking the limit for p+ 0, we find this 
effective pressure at a point (x, 0, 2) due to the given source at 
(A, 0, -f) is 
mr / 2 
p= Spxgrom| ene o(f-2)see? Pcost x .(e—h) seco} sec*@d@, (3) 
0 
for z —Ah<o; and p=o forr-—h>o. 
For a ship form given by y = +F (a,2), we have the usual approxima- 
tion of a source distribution over the section by the plane y = 0, the 
source strength per unit area being 
~ On da © 
For a model of length 27, draft d, with O at the midship section, we 
obtain:— 
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