Naval ARCHITECTURE (continued)

Thus by lightening a ship gradually, and at the same time preserving the direction of her keel, or the angle which the keel makes with the surface of the water, a. variety of water-lines may be drawn parallel to each other, and to the load-water line. See a further illustration of these lines in the article WATER-LINE. See also their figure on a ship's bottom, plate I. fig. 5.

Plate I

The ribbands are likewise of great utility in ship-building; they are narrow and flexible planks placed on the bottom at different heighths, so as to form a sort of mould for stationing the inferior timbers between the principal ones. They differ from the water-lines, inasmuch as the latter have only one curve, which is horizontal, whereas the ribbands, besides their horizontal one, have a vertical curve. To convey a just idea of these curves, which cannot be represented on one draught at their full length, without an oblique section of the ship's length, it will be necessary to have recourse to two planes; that of the elevation, which exhibits their vertical curve; and to the floor-plane, upon which the horizontal curve is expressed. See RIBBANDS.

These different lines are extremely useful in exhibiting the various curves of a ship's bottom, that as they are gradually diminished, their uniformity or irregularity may be discovered by the skilful artist.

We have already observed, that the qualities required in a ship ought to determine the figure of the bottom: a ship of war therefore should be able to sail swiftly, and carry her lower tier of guns sufficiently out of the water. A merchant-ship ought to contain a large cargo of merchant-goods, and be navigated with few hands; and both should be able to carry sail firmly; steer well; drive little to leeward; and sustain the shocks of the sea without being violently strained.

The first thing to be established in the draught of a ship is her length; and as a ship of war, according to her rate, is furnished with a certain number of cannon, which are placed in battery on her decks, it is necessary that a sufficient distance should be lest between the ports to work the guns with facility, and particularly to leave space enough between the foremost gun and the stem, and between the aftmost gun and the stern-post on each side, on account of the arching, or inward curve of the ship towards her extremities.

When the length of a Ship is determined, it is usual to fix her breadth by the dimensions of the midship-beam. On this occasion the shipwrights, for the most part, are conducted by rules founded on their own observation; for having remarked, that some vessels, which by repeated experience have been found to answer all the purposes of navigation, have a certain breadth in proportion to their length, they have interred that it would be improper to depart from this proportion: but as other ships have been constructed with different breadths, which were equally perfect, a variety of different general rules have been adopted by these artists, who are accordingly divided in their opinions about the breadth which ought to be assigned to a ship relatively with her length, whilst each

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