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Second of Two Articles on the Cioens of Wooden Shipbuilding-- This Installment Treats Chiefly of Methods of Fetnee the Lines By Samuel J P. Thearle HE half-breadth plan has next ; to be drawn upon the floor; and here we may again note that lines now being used, which are curved in the body plan, will be straight in the half-breadth plan, and vice versa. Lefore proceeding to copy the half- breadth plan from the body plan, it should be noticed that, owing to the new level. lines which have been pencilled on the sheer drawing, the half-breadth plan to be drawn upon - the floor will be totally dissimilar in appearance to that given in the de- sign. -But if 'the base line of the sheer draught is parallel to the water lines, and the body is therefore given in that drawing as shown in Fig. 5, the additional work of copying the. body by new lines, and then trans- ferring the latter to the half-breadth plan, will be unnecessary. oe "Having already drawn. on the floor the middle line of the half-breadth plan, and the projections of the square stations in that plan we pro- ceed to copy the level lines from the body into the half-breadth plan (see. Pig. 6). Straight-edged battens are set to the middle lines of body and _half- breadth. Then measure on a staff, whose end is kept against the former batten, the distance from the middle line to where a level line ab cuts each square station 1, 2, 3, etc, in the body plan, and transfer these distances to the corresponding square stations in the half-breadth plan, by setting the end of the staff against the mid--- dle line batten of that plan, Then end the level line by making a tan- gent to a circle whose center is the point thus found, and whose radius is equal to the thickness of the bottom plahk taking care to do. so on that side of the circle nearest to the middle line of body. We must again remark that this end- ing is only approximate unless the stem is square to the level line. For the fore edge of the rabbet is assumed to be the axis of a curved cylinder, the radius of which is the thickness of the bottom plank; and the surface of the timbers is supposed to be in contact with this cylinder along the line of the center of rabbet. It is evident, then, that unless the section of the cylinder is made square to the axis it will be elliptical. Another error is, however, introduced owing to the tapered siding of the stem below the lower cheek. Another Method Gives 'Better Results "A more correct ending. is, therefore, obtained by making the level line end as a tangent to an ellipse of greater or less eccentricity in proportion as the stem deviates much or little from the condition mentioned. However,' practi- cally, these endings are sufficiently cor- rect, being within the limits of error to which work is carried out upon the mold-loft floor. ; It is mecessary at this. stage of the work to get in the bearding line, i. ¢., the true line of the after edge of rabbet of stem or, upper edge of rabbet of keel, that given in the sheer draft being not sufficiently cor- rect to be copied from thence to the floor. The bearding line' is: the line of the intersection of the surface of keel, deadwood, stem, and stern post, with the outer surface of the. frame timbers; hence a rough, and, indeed, a common way of finding this line, is by measuring in the body plan the half siding of stem at each level line, and drawing, in the half-breadth plan, a line parallel to the middle line of that plan at a distance equal to the half siding thus found. The inter- section of this parallel line with. the. corresponding level line in the half- breadth plan will be, approximately, a point in the bearding line; and if ihis point be squared into the sheer plan to the corresponding level line, we shall have an approximation to a point in the bearding line in that plan. Other points in the bearding line be- low the level. lines in the sheer are obtained by measuring in the _ half- breadth plan, the half siding of keel at each square station, and drawing a line in the body parallel to the mid- dle line of that plan, and distant from it the half siding thus found; the intersection of this parallel line with the corresponding square station, when transferred to the respective square station in the sheer plan, will be an approximation to a point in the beard- ing line in that plan. There is' an error in this method of obtaining the bearding line due to the same causes as the incorrectness of the endings of ue level lines already referred to. However, it is usually suf- and marking the distances out on the respective square stations. A batten is then bent so as to pass fairly through as many as pos- sible of these points, and the line a, b, is chalked in, this process being performed for each level line. Still referring to Fig. 6, square ficiently correct for all prac- tical purposes, and if slight allowances be made in end- ing the lines by substituting ellipses for circles accord- ing to the discretion of the draftsman, no error worthy of notice will occur. At some yards it is usual to obtain the bearding line and down from the sheer plan to the middle line of the half-breadth plan, the point of intersection a, of the level line with the fore edge of rabbet of stem, and set off on this perpendicu- lar line the half siding of = middle of rabbet by the following method, which is obviously more _ accurate than the preceding, although even this is not theoret- ically correct, as. the taper of the stem is not taken into account. At any Se stem at this height as meas- fae) L RS. LH US. FH. ES. \ x \ » x ES. FH, /S. JH 25. lected points A and C on the fore edge of stem, Fig. 7, ured from the body plan. FIG. 5-WATERLINES AND DIAGONALS. 252 in the sheer plan, about the a at nN ae a al | : : : ,