| LEGEND TO THE ILLUSTRATIONS, SEE BELOW Print Specifics:
Notes:
Legend to the illustrations: If we examine more closely the principles of Seppings's system, which is now adopted in the British navy, we 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 diagonal of a parallelogram, the sides of which are parallel to the supporting forces, drawn through the point from which the supporting forces act a line parallel to the former; then ail 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 prevent the timbers from bending. If we regard AF (figs. 25, 26) as the neutral line from which the curvature extends to both sides, it is evident that nothing but the construction shown in fig. 25 can prevent it, for since A in this figure is supposed to be one of the neutral points of the system, it must be considered as firm, and the inclination to curvature which tends to displace the points H,C,G, and B, as well as the action on the supports AC and AB, according to the weight applied, will operate to stretch the timbers, which coin be prevented only by the application of these bands. But the action of the bands is entirely in the direction of their length, and hence tends to prevent any change of form, so that the force which tends to displace the point C, is removed by the resistance of the brace, AC, and of the band to the firm point F. and thus an additional strength is given also to the point E; the action of the force winch tends to displace the point H, iii common with C, is set aside, by the firmness of the long internal timber AH, and the resistance of the band HF; so that if the materials are sound, no displacement or change of form can take place. If we now consider the opposite construction (fig. 26), it appears from what has been said, that the braces, AC and AB. are exposed to a pressure; and since the point, A, according to the supposition, is neutral, and therefore firm, the pressure must bear upon the point C, and produce a curvature. But the tendency to press upon the point C is not set aside by the action of the band FE, and consequently, since the point F, according to: the supposition, is firm, the tendency to extension in the brace must press upon the point, and still more, consequently, upon tile point G. The point E, thus acted on, must communicate its own inclination to the band EH, and produce a sinking at the point H. Every part of the framework, from C to H, is thus subjected to pressure, and a change in the form of the ship must be the effect. According to Dupin, the main principles in regard to the curvature of vessels are the following. 1. If a vertical plane divides the ship into two parts, so that the weight of each part is equal to the weight of the water which it displaces, then the elements of these parts in respect to this plane, that is to say, the tendency to curvature, will be either a maximum or a minimum. 2. This inclination will be a maximum, when: the infinitely small part which lies on the plane of the element is directly opposite to the plane of the total element. 3. The inclination will be a minimum, when the element on the plane acts parallel to the total element. Let the lines AO (fig. 27) coincide with the surface of the water, the different sections AC, CE, EG, GH, HK, KM, and MO lying in the same. On some of these segments take the triangular surfaces which represent the difference between the weight of the transverse sections and their pressure on the water. On the segment AC == 49, the right-angled triangle == +72 will lie under the water-line, because the weight exceeds the pressure ; onCE == 20, the equilateral triangle CDE == —108, stands above the water-line, because here the pressure exceeds the weight ; on EG == 50 stands the triangle EFG == +118; GH == 6.6 is too small to be taken into account ;on HK == 13.4 is the right-angled triangle HIK == —119, and finally on KM and MO == 17.5 and 19.5, the triangles [KM and NOM==—115 and +192. Now add together the lines, and we have 176 feet as the length of the ship, and for the sum of the differences + 37, so that 37 tons must be removed from the forward part of the ship on account of the pressure, in order to set aside the tendency to curvature. Martin2001 Satisfaction Guaranteed Policy!
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