186 Col. Beaufoy on the Construction of Sails. [Sept. 



it is proposed to give the sails a circular shape, as represented 

 in fig. 5, which may be done in the following manner : The 

 hoist of the sail, A B (fig. 4), the spread of the head, B C, the 

 length of the after-leech, C D,* the dimensions of the curved 

 part (called the roach), D E, and the versed sine, A Z (fig. 5), 

 being fixed, proceed to calculate the radius of a circle that will 

 pass through the three points, C Z D, by dividing the square of 

 half the chord by the versed sine, and to the quotient adding the 

 versed sine, and half the sum is the radius. In this case, A Z 

 is one foot, C D 22 feet 1 inch, or 22-0833 ; the half is 11-0416; 

 the square 121*93 ; to the number add 1 ; and as an unit neither 

 divides nor multiplies, half the sum, 61-465 feet, is the radius. 

 On the radius from Z towards p, set off in succession the width 

 of the canvass of which the sail is to be made, deducting the 

 breadth of the seam, and through these points draw the requisite 

 number of concentric circles, intersecting the roach, A D, gaff, 

 C B, and mast, B A, and the length of the different gores will 

 be obtained by measurement. The distance between the head 

 and fool, of the sail must next be ascertained in those places 

 where the concentric circles cross it, which distances are the 

 chords of the different arcs. With these chords and the radii 

 calculate the lengths of the respective arcs, and the differences 

 between the lengths of the chords and the lengths of the arcs 

 is the quantity of canvass to be gathered up in the inner edge 

 when sewing it to the next cloth; and similar operations are to 

 be performed until the sail be completed. The following table 

 may be found useful in illustrating my meaning. 



* The mainsail when hoisted appears to most advantage when the after-leech is 

 sufficiently long to permit the gaff to be parallel to the fore-part of thejib. 



