499 



of about 1000 tons, acting on a lever one foot in length, while the 

 strain arising from the unequal distribution of the weight, and the 

 displacement, amounts, where it is greatest, to 2600, although it is 

 somewhat less than this exactly in the middle of the vessel. The 

 next force investigated by the author is that of the waves, which he 

 considers as including the consequences of the effect of the wind ; 

 and this he finds capable of becoming much greater than the former, 

 amounting, in particular cases of the effect of a series of waves, to a 

 strain of about 10,000 tons, and their difference more than 6000 

 when the waves are in a contrary direction. Hence it is inferred, 

 that although these occasional strains exceed in magnitude the per- 

 manent causes of arching, they do not by any means make it super- 

 fluous to give the greatest strength to the fabric in the direction 

 which is best calculated for the prevention of that effect. It is 

 also remarked, that when fastenings have once given way to an oc- 

 casional force of this kind, the ship must naturally assume the form 

 which is determined by the operation of more permanent causes ; 

 and this circumstance may lead the inattentive observer to false con- 

 clusions respecting the manner in which the injury has been sustain- 

 ed. The tendency to breaking transversely arises from causes pre- 

 cisely similar to those which have been mentioned as operating lon- 

 gitudinally ; but their precise magnitude does not appear to be easily 

 calculable. The force tending to produce a lateral curvature has com- 

 monly been in some measure neglected, for want of a permanent 

 strain in a similar direction, capable of exhibiting its effects ; but 

 Dr. Young estimates its magnitude, in certain cases of waves striking 

 a ship obliquely, to be nearly or fully equal to that of the vertical 

 strain> as already computed. The manner in which a ship gives way 

 when she strikes the ground is next described ; and the effects of 

 partial moisture in promoting decay are mentioned as the last of the 

 evils which it is the object of the builder to obviate, as far as it is in 

 his power. 



Dr. Young proceeds to consider the arrangements that are best 

 adapted to obviate the various strains which are likely to occur in the 

 fabric of a ship, and observes, that the principal, if not the only, ad- 

 vantage of oblique timbers is in the additional stiffness which they 

 afford ; since the ultimate strength, or the resistance at the point of 

 breaking, is little, if at all, affected by them in the cases which have 

 been proposed for experimental examples, though, in some other 

 cases, the strength as well as the stiffness may be surprisingly in- 

 creased by the obliquity of the substances employed. In a ship, 

 the utility of oblique timbers must depend in great measure on the 

 changes which are observable in cases of arching, whether they con- 

 sist most in an alteration of the angular situation of the parts, or in 

 the want of continuity from a failure of the fastenings. From actual 

 observations made at Chatham, he concludes that half of the effect 

 produced depends on one of these causes, and half on the other ; and 

 infers, that so far as a change of the angular position of the timbers 

 is found to take place, the addition of oblique braces must be of the 

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