38 NAVAL SCIENCES. 



pieces diverge from the other timbers at an angle usually of 45°. In the 

 forward part of the ship, these diagonals run in a different direction from 

 those in the rest of the vessel, and are at a distance of six or seven feet or 

 more from each other. Their upper ends rest against the horizontal frame 

 of the beams of the gun-deck, while their lower ends are supported by the 

 first planks of the kelson, except in the centre, where they meet the planks 

 lying on each side of the kelson in order to receive a part of the pressure 

 of the main-mast, which always bears hard upon the keel, and often with 

 injurious effects. Other timbers are placed in each direction upon the joints 

 of the frame timbers, and connected with the knees and ribs, so as to form 

 an entire system of immovable rhomboidal parts. A beam is placed in each 

 division, in an opposite direction to the inclination of the diagonals, dividing 

 the rhomboids into two equal parts, and according to Seppings these beams 

 are like the key-stone of an arch to the diagonals. This arch-like arrange- 

 ment of the diagonal timbers not only prevents any change in the direction of 

 the length, but also presents a resistance to the outward pressure from below. 



The beam-work in the new system is constructed almost precisely like 

 that of the old, except amidships, where the greatest strength is required, 

 and where Seppings introduces two additional timbers. They are all laid 

 in the inside, either on planks or frames, which are designated by E in Jig. 2. 

 They are connected together at different lengths by dovetails or round 

 pins, so that they form a resistance to the longitudinal pressure. In pi. 9, 

 Jigs. 1 and 2, A is the kelson, with the additional beams'; B, the diagonal 

 timbers ; C, the lengthwise pieces ; D, their braces ; E, the inside frame, 

 supporting the upper part of the diagonals ; F, supports for the braces 

 between the port-holes ; G, braces ; H, blocks under the supporting planks 

 and frames for the iron knees, of which we have a front view in^^. 3. In 

 the old system, the deck planks formed nothing but platforms ; but in the 

 new system (Jig- 5), with the exception of the forecastle, round-house, and 

 quarter-deck, they are laid diagonally, giving an additional support ; Jig. 4 

 shows the construction of a ship's stern on Seppings's plan, with all the 

 braces and necessary iron-work. The helm-port-transom is here left out, 

 which formerly was one of the heaviest and most unmanageable timbers in 

 a ship. 



If we examine more closely the principles of Seppings's system, which is 

 now adopted in the British navy, w^e arrive at the following result. Through 

 the point at which the supporting forces act, draw a line representing the 

 direction and magnitude of the draught power, and taking this as the diago- 

 nal of a parallelogram., the sides of which are parallel to the supporting 

 forces, draw through the point from which the supporting forces act a line 

 parallel to the former ; then all parts of the connexion on the same side of 

 the draught-line will be in a state of pressure, while those on the opposite 

 side are in a state of tension. The first object of the diagonals is to pre- 

 vent the timbers from bending. If we regard AF {pL 7, Jigs. 25, 26) as the 

 neutral line from which the curvature extends to both sides, it is evident 

 that nothing but the construction shown in Jig. 25 can prevent it, for since 

 A in this figure is supposed to be one of the neutral points of the system, it 

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