sheathing of lead fastened on with copper nails had been used as a protection for the timbers from the devastating insects of the Mediterranean. With the decline of Roman greatness came a new era for ship-building. The hardy Norsemen had chopping seas and Atlantic swells to fight with; their ships differed much from the stately galleys and quinqueremes of the empire. Far smaller, they were built more stoutly, with bluff bows, and a lug-sail which could be braced well up to the wind. The Norse ships must have been of considerable power, for there is good evidence that they had visited the coasts of the New World at an early period. We have, however, very little knowledge of the construction of these vessels, except that they had high prows and sterns to resist the waves, and that they were calculated for sailing in opposition to the galleys, which were for rowing. The introduction of galleys by Alfred, pulled by 40 and 60 oars, and twice as long, deep, nimble, and steady as the Danish ships, kept the latter in check; but it also checked the development of ocean-navigation, for the galleys were only fit for shore-service. The ships gradually increased in size. Hardicanute had a galley pulled by 80 oars; and contemporaneously, the Venetians are said to have built ships of 1200 to 2000 tons. William invaded England in miserably small sailing vessels; but large-indeed very large -vessels appear to have existed in the time of Richard I. John systematised ship-building by establishing a royal dockyard at Portsmouth. Large ships constructed for sailing only seem to have come into general use, together with the mariner's compass, in the beginning of the 14th century. One hundred and fifty years later, the addition of the bowsprit added much to the sailing-powers of vessels.

In Ellis's Collection of Letters there is one, dated 1419, from John Alcêtre to King Henry V., concerning a ship building at Bayonne for that monarch. This letter is curious, as shewing how many of the present terms then existed, and also that the Kynges schyppes' were of considerable dimensions (e. g., 'the stemme is in hithe 96 fete; and the post 48 fete; and the kele ys yn leynthe 112 fete.') Before this period, ships had been built strong enough to encounter ice in the whalefishery. From this period the history of shipbuilding is resolved into the history of individual parts, for the main principles of wooden ships were already established. In Henry VII.'s reign, the cumbrous fourth mast began to be dispensed with; in that of his successors, shifting topmasts came into fashion, the lofty stems and sterns (which must have precluded sailing on a wind) fell gradually into disuse. Port-holes were invented at least as early as 1500. In 1567, there were cutterrigged vessels in the British seas. In the century ensuing, naval architecture was much improved by Mr Phineas Pett, his son Peter, and by Sir Anthony Deane; but the best naval architects were not in England. Within the present century, the introduction of steam has led to the building of ships with finer lines, both for bow and stern. About 1836, iron was introduced as a material for shipbuilding, and is now employed almost equally with wood.

Adverting now to the actual art and practice of ship-building, the subject is divisible into two distinct portions-the theoretical, known as Naval Architecture; and the practical, called Ship-building. The naval architect designs the form of a ship with reference to the objects intended in her construction, to the speed required, powers of stowage, &c.; while the ship-builder works from his drawings, and gives practical effect to the theoretical design.

Naval architecture on a theoretic basis is of recent date, for, as in all cases, practical efforts, more or less in the dark, have preceded by many ages the theorems of the man of science; nor is it at present by any means an exact science. Results continually occur which take by surprise the best masters; and great as have been the strides both in theory and practice, many of the most successful ships have been but happy experiments. The laws of flotation and resistance are, of course, the foundation of the science, and for these we must refer to the articles on HYDROSTATICS and HYDRODYNAMICS; but very trifling changes in the shape of the body immersed, the position of its centre of gravity, &c., produce apparently disproportionate results on the sailing-powers of a ship. In regard to speed, the resistance is, theoretically, as the square of the velocity; but, practically, it increases in a greater ratio, since the water piles in a wave before the bows, and leaves a temporary hollow before it closes in at the stern. To avoid this wave at the bow, and give good steerage-power to the rudder, finelypointed extremities are desirable; but if these points be too fine, they will cease to be self-sustaining in the water, and will detract from the general buoyancy of the ship, while they will tend to raise the centre of gravity above the metacentre. Apart from these considerations, the finer the build, the less are the stowage-power and steadiness. It will thus be seen how many points a naval architect has to take into account in designing the lines of a ship. It would be beyond the scope of an elementary article like the present to give the complicated rules by which the areas of sections, solid contents, and centres of gravity of ships are calculated; but it is necessary to say that they have to be computed with the utmost nicety. Theory has as yet failed to point out clearly what should be the proportions between the length, breadth, and depth of a ship; but the following principles may be stated as the results of experience:

An increase of length gives an increase of displacement of water, and therefore of carrying-power; if this be not desired, it allows of tiner lines forward and aft, and consequently greater speed. It also increases the resistance to lee-way. The greater friction of the water on the longer sides does not appear to be material. Against the increase is to be set a diminished power of turning, tacking, and wearing. It also involves a more careful balancing of weights in the fore and after portions of the ship, for the momentum of a small weight may become large in a long vessel, from being such weight multiplied into the square of its distance from the ship's centre of gravity.

The increase of breadth gives greater stability c the ship, and, by allowing of more sail, indirectly greater speed; but directly, it increases the resistance to the water. Of course, greater breadth enables greater bulk to be carried. Depth is a question dependent on the seas to be navigatel, the object for which the ship is intended, and many other reasons. It is to be borne always in mind that the consumption of stores on a long voyage will change the draught of a ship considerably. Practice has proved unequivocally that ships sail better for drawing more water aft than forward.

Passing now to the actual designing of vessels: the architect works on paper only; he has therefore to shew on a flat surface, for the builder's guidance, the exact position, curvature, and relief of every line and point in his proposed structure. He accordingly draws three plans, on each of which every point of the ship is traceable: the sheer-plan, shewing all lines of length and height;

It is then to be decided of what material the ship shall be constructed. Of the many woods employed-oak, teak, and fir, are those most commonly used; or iron may be resorted to; or, again, the ship may be of wood and iron combined. The building of a wooden and of an iron ship are quite distinct operations, the requisite strength being obtained in a different manner in each case. It is necessary, therefore, to consider separately the principles of wooden ship-building and iron shipbuilling; and as the most time-honoured, and as yet the most general process, we will first deal with the art of the shipwright who forms the vessel of timber.

Wooden Ship-building.-The first process is to develop, or 'lay off,' on the mould-loft floor, certain full-size working sections of the required ship. These are taken from the construction drawings, and are built up of planks. The combinations of these pieces of plank shew the shape in which the several timbers will have to be cut, to impart the necessary curvature and strength.

On

The next step in actual construction is to prepare the slipway, by raising a number of strong blocks of timber a short distance apart, on which the keel shall rest, and which shall sustain the entire ship when built. These blocks are composed of several pieces, and it is of the utmost importance that their upper surfaces be in an exact line. That line is made at an inclination of ths of an inch to a foot; and the keel of the ship, and the ship itself, have consequently that slope to the horizon while building. This inclination is for the facility it affords in launching the completed vessel. the blocks is laid the keel, which may be called the back bone, and is certainly by far the most important timber in the ship. From it start the ribs, the stem, and the sternpost; so that any serious accident happening to the keel, involves the breaking up of the whole 'structure. It is therefore made of great strength, being, in a first-rate, no less than 20 inches square. The material is usually elm, on account of its toughness, its non-liability to split, and the fact that immersion in sea-water preserves it. The pieces of which it is composed are united by the strongest kind of scarph joint (see CARPENTRY).

a

of the Keel.

b

To afford a firm footing for the planking of the ship, a rabbet, or angular groove, is cut in the side of the keel, as in fig. 6. Here the side a represents the rabbet, as usually cut in the merchant service; b, as made in the royal navy. The advantage of the latter Fig. 6.-Rabbets system is, that thicker planking can be worked in, affording better lateral support to the keel, and that there is less disruptive leverage when the ship takes the ground. The false keel is placed below the true keel, after all the bolting through the latter has been accomplished. It consists of elm, 4 to 6 inches thick; and is but lightly secured, in order that if the ship runs ashore, the false keel may readily come off, and let the vessel go free. It is so put on that its joints come midway between the scarphs of the keel. To fix it, it is necessary to knock away, one by one, the blocks on which the keel rests, which is done at the time the weight of the ship is transferred from the blocks to the cradle resting on the bilge-ways. See LAUNCH.

What the keel is to the bottom, the stem and sternpost are to the bow and stern of the ship, forming the keys from which the ends of the planking (technically called the 'butts') and all longitudinal supports start. Each is, of necessity, of great strength, and rises from the respective

extremities of the keel. The stem is fastened to the keel by scarphs, called the boxing, and within it is the apron, and perhaps a false-post also, to impart additional strength, as shewn in fig. 7. The stern-post has to bear the rudder, and is usually made, when possible, of one piece of timber; it is united to the keel by a mortise and tenon joint. In large vessels, an inner post is sometimes worked on to the sternpost for extra security. In screwsteamers, there is a second sternpost, forming the for- a, stem; b, keel; c, boxing; Fig. 7.-Stem. ward support for the screw. d, apron; e, stantion.

The extreme outlines of

the ship being now established, the builder proceeds with the timbers to form the bottom and sides, which together constitute the frame, corresponding to the ribs in an animal. The ribs form the sides of the ship, and are placed at from 2 feet 6 inches to 3 feet 9 inches from centre to centre. Above the water-line, the spaces between them are filled in solid with timbers of equal thickness. For this purpose, in the midship-body the keel is crossed at right angles, or nearly so, by certain timbers which form the floor. One mode of arranging the component pieces is shewn in fig. 8. The

keel is let about three-fourths of an inch into a groove running along the bottom of the floor, while above the floor, the keelson is a massive timber, paralel to the keel. The keel and keelson are bolted firmly together by long copper bolts, which pass through the timbers of the floor, and completely fix the latter. Beyond the floor-pieces, and forming the curvature of the sides, are the futtocks. The heels of these timbers rest on the butts of the floor-timbers. There may be a greater or less number of futtocks, according to the size of the ship. On the heads of the uppermost futtocks, rest the heels of the top-timbers, which, with any lengthening pieces which may be necessary to give height, form the complete ribs. The floor, futtocks, top-timbers, and lengthening timbers are united to each other by dowels and bolts. As an additional strengthening to the frame in large vessels, side or sister keelsons are bolted on to the floor or futtocks, a short distance on each side of the principal keelson. Fig. 9 shews a section of a complete rib, with the several parts. Having now formed the ribs for the midship-body, in which they are placed at right angles to the keel, it is necessary to consider their form in the fore and after cant-bodies. Here the right angle can be no longer maintained between the timbers and the keel, since they have to be

called deadwood, shewn in fig. 12. The deadwood consists of timbers worked above the keel, and of the same width with it, and is practically a heightening of the keel. The deadwood imparts a wedgelike shape to the vessel. In screw-steamers, the after-deadwood is almost wholly cut away to form the aperture for the screw.

Having built the main skeleton, as it were, of our ship, the skin is the only thing remaining to com plete its exterior. This is represented by thick wooden planking, fastened on to the ribs, the lowest layer pressing into the rabbet of the keel, and the highest reaching to the uppermost bul wark. The thickest planking is at the bends or wales, marked H in fig. 9, where it varies from 4 inch in small vessels to 10 inch in ships of the first class. Very thick plank is technically termed thickstuff. Below the wales, the planks are reduced gradually in thickness: those first occurring are called the diminishing plank,' still of oak: under this, on the rounding, fir is used under the name of 'bottom plank,' except the last five or six planks from the keel, which are of elm, and are called garboard strakes.' Every complete line of As planking from stem to stern is styled a strake. the trees from which thick planks are cut are parts of cones—i. e., with the plank much wider at base than at top-the planks are worked alternately as in fig. 13, which is called 'top-and-butt.' Other forms

Fig. 9.-Rib and Decks in section. A, keel; B, keelson; C, false keel; D, floor; EE, futtocks; F, top-timber; G, lengthening piece; HH, wales; I, diminishing planks; K, bottom planks: L, garboard strakes: M, beam; N, deck; O, shelf; P, waterway; Q, spirketting; R, clamps; S, knees; T, side-keelsons; V, limber strakes;

W, rough-tree rail; X, mast.

α

the ribs being set at a diminishing angle to the keel, as seen in fig. 10. The foremost cant-timbers are the knightheads, forming, with the stem, a bed for the bowsprit; next to these are the hawsetimbers, through which the hawse-holes are pierced. In order that the cant-timbers may sit firmly on the keel, they are made narrower at the bottom than at the top. But the canting forward Fig. 10.—Cant-body, seen or aft is not the only peculiarity of the cantbodies; for at its extremities the the ship becomes sharp downwards as well as endways. It consequently ceases to be practicable to have floors of any flatness across the keel. The half-floors and

froin above.

a, keel.

first futtocks are made in one piece, slanting more directly upwards; they pass rapidly from their flat position, through that shewn in fig. 11, to the state

Fig. 13.-Planking; top-and-butt.

of working are 'fair-edge' and anchor-stock,' which do not call for particular description, but are less economical than top-and-butt. The planks are fastened to the ribs by bolts; one through each rib constituting 'single fastening;' two, 'double fastening;' and one and two alternately, 'single and double fastening.' 'Dump fastening' consists in using alternately one bolt and one dump or bolt-nail, which is hammered to a head without and within. Wooden treenails are, however, frequently employed, as less in weight than copper, and less liable to split the wood. The comparative utility of wood and copper fastenings for the strakes, is still a disputed point.

In a well-constructed ship, the filling in of the timbers to a level above the water-line should be so accurately formed that she would float without her planking; but when the latter has been well caulked, it is certain that it adds greatly to the dryness of the ship, while it aids materially in binding her several parts together.

The

At frequent intervals across the ship, and at the heights of the several decks, are inserted the beams, which are solid masses of timber, either in one piece or scarphed. These prevent the ship from collapsing, and at the same time support the decks. beams and decks are shewn at M and N respectively in fig. 9. To support the beams on each level, a strong timber or shelf is worked round the interior of the ribs. Above the ends of the beams, similar timbers or waterways, though somewhat smaller, are worked round the inner frame. The inside is planked above the water-line similarly to the outside. The planks above the waterways as high as the ports or windows are spirketting (Q), those below the shelf and above the ports are the clamps (R). The decks and beams curve upwards at the middle, forming a very depressed arch, partly for drainage, and, in men-of-war, partly to counteract the recoil of the guns. When weight is piled on