A much better arrangement is to place them alternately in the two rows, as shown in fig. 63. Rivets arranged in that way are said to be _staggered_, or placed _zigzag_. The method of laying off the holes and proportioning such a seam in order to get the most strength is, first, to determine the greatest distance which can be allowed between the rivet-holes, and yet keep the seams water-tight. Supposing this is 1⁵⁄₁₆ inches,[32] with plates ³⁄₈ inch thick, the diameter of rivet whose sectional area will give an equal amount of strength must then be calculated. From the preceding data it will be found that for drilled plates the resistance of the portion left between such holes will be 22,148 pounds, and a rivet ³⁄₄ inch in diameter will have a resistance of 22,085 pounds. On the line _a b_, fig. 63, which is to be the first row of rivets, we will draw one hole, _c_. From the center of this hole we will describe the arc of a circle, _d e_, with a radius, _c d_, equal to the sum of the distance between the holes, 1³⁄₈ inches, and one-half the diameter of the hole, or ³⁄₈ inch, making the radius 1³⁄₄ inches. From _d_, the intersection of this arc with the line of rivets, _a b_, with the same radius, we will step off the distance _d f_ will then be the centre of the second rivet-hole on the line _a_, _b_. The rivet can therefore be drawn, and from its centre, with the same radius employed before, another arc, _d g_, should be drawn. If now we draw a rivet-hole (_h_) between the two arcs and touching each of them, we will have all three of the holes so arranged that the metal between the holes _c_, _f_, will be just equal to that between them and the hole _h_. In other words, the strength of the plates on the line _c f_ is just the same as on the line _c h f_. Therefore the strength of the plates on the straight line _a b_ is just the same as on the zigzag line _c h f_, etc. The strength of this seam would therefore be as follows: Plates through rivet-holes (tearing) 110,742 lbs. Rivets (shearing) 110,425 lbs. Plates in front of rivets (crushing) 126,562 lbs. Solid plates (tearing) 158,205 lbs. [32] That and even greater distances between the edges of the holes are now used successfully with ³⁄₈-inch plates. The weakest portion of this seam, it will be seen, has a strength of 70 per cent. of the plate, or is 38 per cent. stronger than a single-riveted seam with punched holes. If we were to use ⁷⁄₈ inch rivets and make the spaces between them 1³⁄₄ inches, the strength of a similar seam would be as follows: Plates through rivet-holes (tearing) 147,656 lbs. Rivets (shearing) 150,325 lbs. Plates in front of rivets (crushing) 147,656 lbs. Solid plates (tearing) 205,078 lbs.