458 
ME. E. J. REED ON THE UNEQUAL DISTRIBUTION OE 
results may be neglected in comparison with the effect of the vertical forces, much more 
may the true bending effect of the fluid pressure be neglected. For the wave-crest I 
find that the water-level at the midship section is about 7^ feet above that in still water ; 
and that if the level were uniform throughout the ship’s length (which it by no means 
is) this immersion would give a pressure of about 620 tons, the bending effect of which 
would be about 3700 foot-tons. This is certainly much greater than the true bending 
effect, yet it only reaches about one twelfth of the bending-moment due to vertical forces 
on the wave-crest. In the wave-hollow similar results are obtained. The water-level at 
the bow and stern then rises about 11 feet above that in still water; and supposing this 
level to be uniform throughout the length, the pressure on the midship section would 
be about 770 tons, producing a bending-moment of about 3450 foot-tons — that is to say, 
about one fourteenth of the bending-moment due to vertical forces in the wave-hollow. 
The true bending-moment of the pressure would be less than this, and might conse- 
quently be neglected. Hence we are confirmed in the opinion that for ships at sea it is 
only necessary to consider vertical forces. 
I must now pass on to notice briefly the longitudinal strains of ships in exceptional 
positions — such as those produced by launching, grounding, and other causes. Although 
exceptional, these strains undoubtedly occur ; and their effect may be, as I shall show, 
more severe than that of any of the statical strains to which approximations have been 
made. Preceding writers have recognized this fact to some extent, but no author has 
done so much as Mr. Fairbairn towards giving quantitative expressions to these excep- 
tional strains. 
Bouguer, Romme, and other early writers had a very clear conception of the principal 
causes of launching-strains. They call attention to the fact that in all, or nearly all, 
launches the ship’s bow or stern is water-borne before the other end has left the launch- 
ing-ways, and that this cannot be prevented altogether even when the ways are extended 
further out into the water than is customary. Some of them go so far as to urge the 
policy of building ships in dock in order to avoid these strains, and support their opinion 
by statements of the large amount of “ breakage ” that takes place when a ship is set 
afloat for the first time from a slip-way. Others combat this opinion, and show by actual 
examples that ships built in dock also break when they are floated, although the breakage 
is not always so considerable as when ships are launched ; so that the severity of the 
strains due to launching cannot be estimated simply by the amount of breakage. The 
latter opinion is undoubtedly the correct one ; and the breakage recorded for wood ships 
when launched may be regarded as due in part to what is termed the ship’s “ settling ” 
in her new position afloat — that is, to her reaching such a condition as to make her 
powers of resistance balance the bending-moments due to the unequal distribution of 
the weight and buoyancy. In part, however, the breakage is undoubtedly due to the 
dynamical strains connected with launching ; and although we cannot separate the effects 
produced by these two causes, we may very properly regard the amount of the breakage 
as to some extent a measure of the relation between the strength of the structure and 
