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all large vessels to bend from head to stern when first 

 launched, by reason of the great weight of the two extremities, and 

 the little support at these parts in comparison with the centre, which, 

 from its greater breadth, sustains an over-large proportion of the 

 whole pressure. 



This defect of the common structure is shown by reference to a 

 common field gate, which, without the diagonal piece, or brace, would 

 soon fail at every joint, but, when braced, partakes of the advantage 

 of the triangular structure, the principle of which, when correctly 

 applied, occasions the whole stress to be diverted from the transverse 

 direction of the timbers employed, and thrown into that of their 

 length, in \vhich their strength is greatest. 



Accordingly, in the new system of ship-building here described, 

 the object of the author has been to introduce diagonal timbers and 

 planks in as many parts of the fabric as could well be accomplished. 



In the first place, a diagonal timber is introduced between the up- 

 right timbers in each interval between the ports ; secondly, instead 

 of the lining, which it has hitherto been the custom to place within 

 the frame, a diagonal timber- work is introduced, intersecting the 

 timbers of the frame at angles of 45, and about six or seven feet 

 asunder, with their upper ends abutting against what are called the 

 shelf-pieces of the gun-deck beams, and having their lower ends sup- 

 ported by the timber strakes. Between these are also placed other 

 timbers, equally inclined, but in an opposite direction, so as to pre- 

 sent a rhombic net-work, which is dowelled to the original frame, 

 and is itself further strengthened by short pieces placed diagonally 

 from corner to corner of each rhombic compartment. 



Beside the addition which is thus made to the strength of the sides 

 of the vessel, these sides are also more firmly united together by an 

 improved construction of the knees, by which the transverse beams 

 are united to them. A degree of unity and firmness is also given to 

 the decks by an oblique position of the planks, which, upon the same 

 principle as before, brace the beams and joists, and resist that yield- 

 ing of the joints which would otherwise take place in their rectangu- 

 lar construction. 



The object of the author has been to give as much inflexibility as 

 possible to every part of the hull ; for in this part he conceives that 

 unbending stiffness is better calculated than any yielding elasticity 

 to resist those forces to which this portion of the vessel is liable ; for 

 though a hope has been entertained, that the known weakness of the 

 common construction might lessen the violence of sudden shocks, by 

 allowing each part to yield in some measure to the force impressed, 

 this conception, he thinks, is not founded on any distinct knowledge 

 of principles, and could not be entertained by those who consider 

 that yielding does not imply elasticity, and who observe, that those 

 parts which yield instead of recoiling with equal force, only become 

 progressively weaker, in consequence of the violence they sustain. 



In addition to the foregoing means of bracing by oblique position 

 of timber^ and decks, Mr. Seppings has introduced another practice, 

 2 K 



