Page:The American Cyclopædia (1879) Volume XIV.djvu/890

 864 snip any outward deviation of the npper timbers that make the cradle in which the ship is held as 'the whole slides down together. This second system is loosely piled up under the ship, the lowest portion being timbers smooth and well greased on the under side and laid directly on the ways. Between these timbers, called the bilgeways, and the bottom of the ship over them, the space is filled in partly with blocks of timber and planks, and toward the bow and stern by short shores, called pop- pets, set up from the bilgeways to the bottom of the ship, their steadiness being secured by stout planks temporarily fastened along the bottom against the heads of the poppets. Near the stem and stern chains are passed across to hold the cradle together. To the front of the timbers of the cradle are fastened ropes that are passed over the bow into the ship, and are intended to hold these when they float away from under the vessel. To bring the weight of the ship upon the cradle after this is fitted under it, long wedges are driven in over the bilgeways from one or both sides of each of them. The shores at the sides of the ship, which had heretofore aided to sustain her, and the blocks beneath the keel, which took the chief portion of the weight, may now be re- moved, with the exception of a few^f the lat- ter under the forward part of the vessel. All this preparatory work is done on the rise of the tide ; and when this is at about its height, and two short shores, called dog shores, have been placed, one on each side the vessel, to brace from the ways as a fixed point forward against the bilgeways, and thus hold the cradle with its load from sliding too soon, the fore blocks are split up with wedges and drawn out, letting the whole weight settle down on the ways. At an order the dog shores are knocked down, and the structure begins to move, at first slowly and then with rapidly in- creasing velocity. In rivers and contracted places the course of the vessel is checked by a hawser made fast on shore, or she is brought up by letting go an anchor. The French have long practised launching vessels without side ways, the weight being entirely supported upon a sliding plank fitted under the keel. A strip of timber is fastened along under the bilge on each side, and a few timbers are laid up in the usual place of the ways, reaching within about half an inch of these strips. It is not expected that they will come in contact except in case of the vessel heeling, when they will serve to prevent her falling over. After the launch the vessel is conducted to the wharf to receive her spars, rigging, and machinery, if a steam vessel, and interior finish ; or she may be taken into the dry dock to be sheathed. It is important to protect the bottom of a vessel with a metallic covering, as without this it soon collects an incrustation of marine vegeta- ble and animal bodies, which seriously inter- feres with their progress through the water, and the timbers are liable to be attacked by the ship worm. Sheet lead was used in an- cient times, and sheet copper was first applied to the ships of the royal navy in 1783. The great expense incurred in suits of copper, which need frequent replacing, is much reduced by the use of Muntz's yellow metal, a combination of copper and zinc described in the article BRASS. The metallic sheets are of different thicknesses for surfaces more or less exposed, the weights being 32, 28, 18, and 16 oz. to the square foot. The thickest sheets are used for the bow and about the load water line. The size of the sheets is 4 ft. by 14 in., and a 120- gun ship would require of them 4,444. They are fastened with copper nails, and are laid so that each sheet laps upon the edge of the next one to it behind and below. Masts and Rigging. The spars include the masts, yards, booms, and gaffs, used to support the rigging and sails. The masts of the smaller vessels are single sticks of pine timber well rounded and with a gentle taper. For large ships it is necessary, on account of the size of the masts, to construct them of a central stick of a num- ber of sides, with longitudinal pieces closely fitted and securely attached to them and then hooped with iron ; these are called made masts, and are stronger than the single sticks of the same size. Hollow masts of plate iron are in use, particularly for iron vessels. Rules for the length of the mainmast of a ship have been half the sum of the length of the load water line and the main breadth of the vessel, and also twice the breadth added to the depth. About the head of each of the lower masts are framed timbers making a horizontal scaffold- ing or platform, which is known as the top. On large ships it is railed around, and on ves- sels of war it used to be the custom to station men in it during an engagement armed with muskets. Upon the rounded front edge of the top stands the topmast, secured in part by passing above through a strong iron-bound flat block set horizontally upon the upper ex- tremity of the lower mast and called a cap. The topmast is about three fifths the length of the lower mast ; and above it succeed in like manner the topgallant mast and royal mast ; and in seas where the prevailing winds are light and are felt more aloft, still another mast is added, called the skysail mast. At the head of the topmasts are cross trees in place of the top on the lower masts. Each of these masts carries its own yard, from which de- pends the square sail designated by the same name as the mast to which it belongs. Its lower corners are sheeted out to the extrem- ities of the yard below, or, in case of the courses or lower sails, to the deck. The yards slide up and down their masts, the lower yards hanging in slings by their middle part, and most of them by lifts attached to the yard- arms, and passing thence through a block at the head of the mast. The foremast is about one tenth shorter than the mainmast, and is furnished with similar yards, rigging, and