The amount of lead required for the bulb at the bottom of the fin can be determined by loading the hull with weights until it is sunk to the water line. The weights will, of course, represent the weight of lead required. This can be cast in a mould and riveted to the bottom of the fin.
[30] To find the number of square feet in the cleats, first find the number of "running" feet, that is, the total length of the cleats if they were stretched out in a long line, like one of the rails of a railroad track. Then, as the cleats are 3" wide (or one fourth of a foot), it will take four running feet to make one square foot. Therefore divide the number of running feet by four and the quotient will be the number of square feet.
[31] Boards twelve feet long will be the best to buy for this house, because you can get two lengths from each board without waste. You could not be sure, however, of getting two lengths of exactly six feet from each twelve-foot board, because the ends are frequently checked or damaged in some way; so it will be safest to make the length 5' 10", as given above.
[32] If you have only small stones or blocks upon which to rest it, the building can be put together directly upon the ground, the sills being rested temporarily upon any material at hand, and then the supports adjusted underneath.
[33] You can mark a point on one string 3' from one stake and a point on the other string 4' from the same stake, and then increase or decrease the angle made by the two strings until another string exactly 5' long will just reach from the marked point on one string to that on the other. This process is based on the principle of mathematics that if the two sides of a right-angled triangle are respectively 3 units and 4 units in length, the length of the hypothenuse will be 5 units. Another way, if you are fond of mathematics, is to find the length of the diagonals of the plan of the house by extracting the square root of the sum of the squares of the two sides. (The square described on the hypothenuse of a right-angled triangle is equal to the sum of the squares described on the other two sides.) You can measure the diagonal directly from a plan if you understand mechanical drawing well enough to make an accurate plan on a scale of perhaps ½" or 1" to a foot. Then take one tape, or string, measuring the width of the building, with one end held on the stake C (Fig. 387), and another tape measuring the length of the diagonal, with the end held on the stake D. Drive the stake A at the point where the two tapes meet when brought together. Reversing the positions of the tapes will give in the same way the fourth corner B. The distance A B should equal C D.
Fig. 387.
[34] The part of the post which is embedded in the ground is sometimes charred or painted to preserve it from decay. This can be easily done, but the process is advisable only with thoroughly seasoned wood. It is highly injurious to green timber, as by closing the pores and obstructing evaporation from the surface it prevents the seasoning of the wood and causes fermentation and decay within (see [Appendix]).
[35] These posts, and even the sills, can be built up if necessary of 2" × 4" studding, two pieces being placed side by side and nailed together, but this is not so desirable as regards strength, its only advantage consisting in the readiness with which the joints can be made by simply cutting one of the two pieces shorter than the other.
[36] Obtained through the courtesy of Mr. Charles H. Bradley, Superintendent of the admirable Farm School on Thompson's Island, in Boston Harbour, where this little village was built.