PLATE XI.
Pl. XI.
Fig. 1.—The Sheer-Crane at Duff’s Wharf. a a a are the working-sheers, to the upper extremity of which the purchase-chain a, e, g, is attached; from the hook marked i, the stone k is suspended by the sling-chain i, k, which was lengthened or shortened according to the state of the tide. b b are the upright-sheers; c c the diagonal or supporting sheers. Those last, though acting as braces, had also a motion upon the connecting block d at the top, from which the pulley e is suspended, and over which the purchase-chain passes. This motion had the effect of giving the stone a kant inwards, when the working-sheers came to the perpendicular, so as to lay it upon the waggon f, to be wheeled along the railways, as will be understood by examining [Plate XVIII.] The crab or winch machine g g, fixed upon the Rock at one side of the railway, with batts and spear-bolts, was worked with a less or greater purchase, according to the weight of the stone to be lifted. The large wheel measuring 3 feet 3 inches in diameter, formed the single purchase, and the smaller wheel of 2 feet 6 inches, with its pinion of 6 inches, when connected with the former by an intermediate pinion, formed the greater purchase, exerting a power in the one case in the ratio of about 20 to 1, and in the other of 98 to 1.
Fig. 2. is a front view of the machine described above, with corresponding letters. At letters h h, will be seen more distinctly the cast-iron bed, with the snugs or flanges for the reception of the lower ends of the sheers a a a and b b b b, with their journal-bolts. This apparatus, along with the other parts of the works, have been modelled for preservation.
Fig. 3. represents one of the malleable iron Lewis-batts, with which the stones were lifted from stage to stage, after leaving the hands of the stone-cutter. This useful implement consists of six members, viz. the palm, which is in three pieces, marked a, b, c; the palm-bolt d d; the shackle e. The spear-bolt f, for preventing the palm-bolt from drawing, was seldom used in practice.
Fig. 4. is a section of one of the praam-boats, shewing her cargo on deck, and more particularly the form and application of the mushroom-anchor and chain-moorings of the Bell Rock craft. a a is the cargo upon deck; b b is the hold or compartment under deck, calculated to contain a sufficient number of empty casks, for floating her, in the event of receiving injury at the rock. c c mark the fore and after peaks, for containing warps, kedge-anchors, grapplings, defenders, and other tackle; d marks the position of the bits and cross-tree to which a hook at e was fixed, for attaching the end of the mooring-chain; f is the slit in the stem, answerable to a hawse-hole, through which the mooring-chain passed almost on a level with the deep water-line, and was ultimately fixed by the ring g, to the lower swivel of the floating buoy h, and also with the mushroom-anchor i at the bottom, connected with a length of chain extending to about twice the depth of the water.
The detached diagram towards the stern of the praam-boat, consisting of a mushroom-anchor, a larger and smaller floating buoy, with their respective chains, represent the state of the moorings while the praam-boats were employed at the Rock. The small buoy k, with its chain l, was connected at the ring accented l´ to the hawser-chain of the praam. When she was unmoored, this small buoy prevented the end of the chain from sinking. In this manner the praams were conveniently disengaged, or attached to the large buoy h. When at their moorings, the small buoy k was unhooked and stowed below, the strong mooring-chain being now drawn through the hawse, or slit at f, and the ring at l´ being simply laid into the hook at e.
Fig. 5. is a perspective view of the sloop Smeaton at her moorings, delivering a cargo of stones, with one of the praam-boats along-side. In the back ground, the Light-house is seen partly built, together with the Beacon-house. Two of the three figures shewn on the deck, near the mast, are working the winch-machine of the ship in raising a stone from the hold, while the figure, in a lying posture, is holding-on the end of the tackle-fall, as described at page [144]. A stone is seen in the main hatch of the ship, suspended from the end of a short boom nearly at right angles to the mast. The figure near the companion or cabin-stair is working one of the guy-tackles. On the praam’s deck, part of a cargo may be seen, and the figure towards her stern is laying hold of the stone, suspended in the tackle, to guide it to its birth, while the other contiguous figure is working an opposite guy-tackle. To avoid confusion, only five figures are here introduced. The praam-boat is understood to be lashed head and stern to the ship, having three or four large wooden defenders slung between them, to prevent the vessels from injuring each other with the undulating motion of the sea. The Smeaton’s sails are handed, and the main and gaff-booms braced to one side, to give room upon deck, in bringing the stones out of the hold. The only peculiarities about the fitting of the Smeaton, were her large main hatch, for the conveniency of loading and discharging; her winch-machine was pretty powerful, exerting a force in the ratio of about 20 to 1, independently of the purchase-tackle; her cargo was also carried upon a temporary platform laid in the hold.
Fig. 6. is a perspective view of the smith’s forge, which was partly fixed with batts upon the Rock; and also of the Foundation-pit, with a number of figures pumping water from the excavated site of the Light-house. The pumps for this purpose were laid in an inclined direction, made of a square form, and very simple in their construction; the pump-spear with its leathern valve, being worked by the artificers, who laid hold of a rope attached to the end of it. In the back ground of this diagram, the Floating-light is seen as if through the haze of the atmosphere.
Fig. 7. represents an Attending-boat, occasionally used during the summer months for visiting the Rock, and relieving the light-keepers. a a is a section of the principal boat, measuring 22 feet in length of keel, and equipped in her rigging after the manner technically termed Lateen-sails, which were originally introduced into use on the Firth of Forth by Mr Thomas Bruce of Grangemuir. These sails are considered more safe than the common lug-sail, from their greatest breadth being carried very low on the mast. But the chief peculiarity of this boat is the launch or “two-half boat” of Mr James Bruce, which she carries, for more conveniently communicating with the Rock, as alluded to at page [412], and further described in Thomson’s Annals of Philosophy, vol. viii. p. 58. In this diagram b is the two-half boat, stowed the one-half within the other, between the main and fore masts, c c the two halves about to be joined and used as one boat, d d the stern view of these boats in a separated state, e e the chatter and catch-bolt for connecting the boats together, after the manner of a ship’s rudder, f f f f the bolt holes, by which the upper parts of the boats are connected and held together.