To obviate this difficulty is the end proposed in the plan under consideration. It does not appear, from any thing which has been presented to the Committee, that Mr. Clark proposes anything novel in the construction of the lower part of the railway, or of the carriage upon which the vessel is to be drawn up; its distinguishing feature being the means provided for removing vessels out of the direct line of the main railway, and of depositing them upon sub-ways, for the purpose of being repaired. To accomplish this purpose the upper part of the railway, for a length sufficient to receive a vessel, is detached from the lower part, and is made capable or revolving upon a firm horizontal platform, a perpendicular shaft from which passes through the upper end of the detached part of the railway. This platform is the segment of a circle, but it may, if necessary, present a complete circle. At the periphery of this segment, the fixed part of the railway terminates, and the detached revolving commences; this is supported upon the platform by a sufficient number of strong iron rollers, placed transversely on the lower part of the framework of which it is formed.
The upright shaft, around which the detached railway is capable of revolving, is also the shaft of the windlass, by which the vessels are to be drawn up; this detached way may therefore be considered as a radius to the circle, of which the platform is a segment. When a ship is drawn up and has arrived upon the movable part of the railway, a power may be applied to carry this with its load to the requisite distance round the circular platform, until it arrives at a sub-way, several of which are erected round the platform, forming produced radii to the circle. These are precisely similar to the main railway, with the exception of their not being continued to the water, but only of such a length as to admit of the carriage with its load being lowered, and deposited upon them until the intended repairs are made.
In the drawingwhich accompanies thisreportthere are represented six sub-ways, and of course upon such a structure seven vessels might be placed at a time. The main expense attending the erection of marine railways, is in constructing that part which is under water, where nearly the whole of the labour must be performed in the diving-bell. In the mode proposed by Mr. Clark, one marine railway would be sufficient in those parts where many vessels may be required to be hauled up; a considerable number of sub-ways, with their appurtenances, might undoubtedly be provided at an expense far below that which would attend the original structure. After maturely considering the subject, the Committee are fully convinced of the practicability of the plan, and also of its economy, in those situations where more than a single railway would be desirable. When once constructed, it possesses the advantage of being capable of extension in the number of its sub-ways, whenever it may be required." Annexed are engravings from the drawings referred to. Fig. 1 is a bird's eye view of the platform and railways. A, revolving section of the railway, which may at pleasure be made to coincide and connect with the radiating or sub-ways BBB, or with the main railway C, extending into the water.
D is the shaft or pivot upon which the section A revolves. Fig. 2 represents the revolving section, with its centre, as in Fig. I, together with the circular iron railways, upon which the cast-iron rollers are to run. Fig. 3 is an elevation or side view of the revolving and permanent railways, supporting a ship's carriage; A being the revolving section; BorC, section of the main, or the sub-railway; D shaft for communicating to the windlass the power which is generated at the levers d; this shaft is also the pivot around which the section A is made to revolve; e e e e, etc, are iron rollers connected to and supporting the revolving section in the circular railways; G, ship's carriage resting on the inclined railways; H, windlass or other machinery for elevating vessels; i, chain by which the carriage is drawn up; k, palls to prevent the carriage from running back; l, friction-rollers, lying between the movable and fixed ways. Fig. 4, ground view of a ship's carriage. Fig. 5, transverse view on a larger scale of a ship's carriage on the railways; a a cuneiform blocks, movable on rollers, in appropriate grooves, to prevent lateral motion; b b, bilge blocks moving on pivots, and resting on rollers adapted to a a; c c, ropes by which the cuneiform or wedge blocks are drawn up, and the bilge blocks forced against, and adapted to, the bottoms of vessels. - Franklin Journal. For a variety of information of the constituent parts of ships, with their recent ameliorations, see the separate heads, as Masts, Rudders, Capstan, Windlass, Blocks, Anchors, Fids, Boats, etc. etc.