862 SHIP iron plates or straps are now commonly em- ployed in all important wooden ships for diag- onal bracing. Diagonal braces are from to | in* thick, and from 3 in. to 5 in. wide, laid at an angle of 45 with the keel. There are two tiers, which cross each other at right angles, and end on a belt of iron above the spar deck, called a head strap, somewhat larger than the diagonal straps. Straps are put either inside or outside of the frame in the merchant service; in the United States navy it is cus- tomary to put them inside. As wooden ves- sels now are not so deep in proportion to their length as in former years, the strength secured by this system of iron strapping is indispensa- ble. In designing a ship, the old plan, after deciding on her tonnage, is to determine the proper midship section for the proposed capa- city, with due reference to the desired speed, degree of stability, &c. The next thing is to plan the horizontal section called the load water section, and then prepare the drawing on a scale of a quarter of an inch to the foot. The three principal draughts are known as the sheer plan, the half breadth plan, and the body plap. The first is a vertical section ex- tending the whole length of the ship, and pre- senting her full depth, the inclination of her stem and stern, her masts, ports, water lines, and generally whatever belongs to the side of the ship. The water lines are drawn straight and parallel, numbered from stem to stern. The half breadth plan is a horizontal section of half the ship divided lengthwise as seen from above. The several water lines, num- bered as in the sheer plan, are dotted in, or drawn in blue ink, and designate the width and horizontal curves of the hull at the dif- ferent levels. The body plan is a midship sec- tion, representing the height and breadth of this portion of the ship ; it is divided vertically into halves, that to the left showing the curves and arrangement of the timbers toward the stern, and the other those toward the bow; the heights of the several water lines are also indicated. Instead of these plans, the Ameri- can ship builder has generally substituted a half model of the vessel built up of thin strips of wood laid horizontally upon each other. These strips represent the parallel water lines, and can be taken apart for any alteration of the plan, or for laying off from them the full size lines upon the floor of the moulding loft. This loft is a large room specially devoted to the preparation of the designs and patterns from which all the timbers are to be shaped. The designs being drawn upon the floor, the plank patterns or moulds are obtained from them, which are of the exact dimensions of one face of the timber, and are furnished with marks that designate the other dimensions. The ship yard is situated by the edge of the water, and sufficiently elevated to secure a proper slope for the completed vessel to slide down the ways. At a convenient distance out of the reach of the tide a row of blocks, 4 ft. or more apart and 3 ft. high, is set in the ground, extending back from the water the proposed length of the ship, and their flat upper surface sloping toward it about 3 from the horizontal. On these blocks the timbers which make the keel are laid, being nicely fitted together by scarfing and secured by bolts. In Europe elm is preferred for the keel, being tough, holding the fastenings well, and long remaining sound under water ; but in the Uni- ted States live oak is commonly used. The latter is the most valuable native timber em- ployed in ship building ; but white oak of second growth obtained near the coast in New England is also excellent, and far superior to the same timber brought from the interior. Locust and cedar are strong and durable, and hackmatack is valuable for knees. Chestnut is employed to some extent, and white and yellow pine largely, the latter being the best foF decks. It is recommended that the trees be killed by girdling in the beginning of the winter when the sap is down, and left to dry and harden before they are felled. After this the timber should be stored in a dry airy place to season. False keels or shoes are from 4 to 6 in. thick, and fastened to the lower side of the main keel with spikes or short bolts, after the frame bolts, which pass through the frame and the main keel, are clinched. The chief object of the false keel is to save the main keel from injury in case the ship should strike the bottom. Ships are generally built with the stern nearest the water, although sometimes it is more convenient to build and launch sidewise. On the fore end of the keel is erected the stem, on the after end tho stern post, with its lower end tenoned into the keel. The frames which cross the keel are formed of floor timbers and futtocks. They are put together while in a horizontal position, with the floor timbers lying across the keel. When all are calked and bolted together the whole frame is canted up by proper purchases, cross pawls preventing it from spreading. The frames thus crossing the keel are called square frames, as they are placed at right angles to the keel ; forward and abaft of the square frames are the "cants" or cant frames, so called because they cant toward the round of the bow or stern. The keelson is a longitu- dinal timber parallel to the keel, and occupy- ing a place on the inside of the frames corre- sponding to that of the keel on the outside. The spaces between the frames are generally filled in solid with white or live oak timber. The keelson is built in one or more pieces varying with the size of the vessel. After the frames are erected they are regulated so as to stand square with the keel longitudinally and level transversely. Heavy- rib bands are at- tached to the frames on the outside, and se- cured by heavy shores. The inside of the ship is then prepared for strapping, ceiling, placing and kneeing of beams, laying decks, &c. The outside of the frame is covered with plank
