ON THE CONSTRUCTION OF SHIPS IN THE MERCANTILE NAVY.
It is remarkable that most of the investigations of fered to the public notice respecting shipbuilding have an especial reference to the construction of ships of war, their ingenious authors seeming to overlook the great variety of vessels which constitute our com mercial marine. That the country is deeply interest ed in whatever relates to commerce, that great sourte of our national wealth, there can be no question; and when we know that the tonnage of British shipping belonging to the ports of the united kingdom, amounts on en average to nearly a million and a half annually, transporting from thence the varied products of Bri tish industry and skill to every quarter of the globe, it would be unpardonable in an article on shipbuild ing., not to make some brief allusion to a subject of so important a kind.
There is a serious and important defect in the pre sent construction of mercantile ships, as regards the putting together of their ribs or frames, and the gen •ral arrangement of the materials.
in forming the frames or ribs, half the timbers only are united so (IS 10 constitute any part of the arch; every alternate couple only being connected together, the intermediate timbers, termed fillings, being entirely unconnected with each other, resting only on the outer planking, without contributing in any degree towards its support. It must be evident that ships so con structed can by no means possess equal strength with such as have the whole of their timbers formed into uniform frames or arches.
This loose, dangerous, and very imperfect mode of shipbuilding, is. according to Sir Robert Seppings, peculiar to the English merchant shipbuilder; and we know even that it is only in latter years that the same system of building has been abandoned in the king's dock yards, while the preferable system of connecting the ribs was common to other maritime powers.
The principle of uniting the frames, lately intro duced in the construction of ships of war, might without doubt, be advantageously introduced into the mercantile navy; a system which would communicate to the ships of our commercial marine much addition al strength and increased durability, without adling to the expense of building.
But the present mode of joining together the ses er al pieces of the same rib, is open also to the heaviest objections. The method adopted is by introducing a third piece, technically termed a chock or wedge piece, as in Fig. 1. Plate D. of which pieces the number amounts to upwards of 450 in a 74 gun ship, and to not less than that number in an Indianian of 1200 tons, and to which class of ships the subsequent drawings to be referred to have an especial reference. Of these chocks. not one in a hundred is ever replaced on the general repair of a ship; for they are not only found defective, but very generally to have communicated their own decay to the timbers to which they are at tached. Besides this the grain of the rib pieces being much cut to give them the curvature required, contri butes in a very considerable degree to the general weakening of the fabric. That they occasion a great consumption of materials is very obvious, as the ends of the two rib pieces must be first cut away, and then replaced by the chock.
The introduction of chocks was done with the view of obtaining that curvature which is so necessary in the formation of a ship, when crooked or compass tim ber became scarce, Its may be seen by a reference to Fig. 2. which describes the shape of a piece of tim ber in the converted form; and by which also it will be perceived that the introduction of the chocks as sists in obtaining the required curve.
The frames of a mercantile ship. on the present mode of building, before they are placed and united to each other, may be seen in Fig. 3. with their chocks or wedge pieces. To the. evils already stated of the present practice,may be added that of imperfect work manship, so that the surfaces of the chocks are sel dom in contact with the surfaces of the timbers. The ends of both are moreover frequently reduced so thin, as to split by the fastenings that are necessary to se cure the planks to the ribs; and thus the ship, in the event of grounding, or even in the ordinary act of rolling, derives little support from timbers united only in fact by two narrow edges.