Before we enter upon I he mode of combining, and the means used to unite the several pieces of timber and metals which constitute a ship, so as to form a whole, we must necessarily digress to give sonic ac count of the new mode of construction introduced into his Majesty's navy in the year 1810, by Sir Ro bert Seppings, who is now surveyor of the royal navy, with the modification which time and experience have enabled him to introduce to bring the plan to its pre sent state of perfection.
The chief circumstances to be guarded against in shipbuilding are, a transverse alteration of form by a separation of one side of the ship from the other, but principally a longitudinal one by the two ends being depressed and the middle rising, which is termed arching or or in sonic cases the middle sink ing, which is called sagging. The transverse altera tion results generally from an imperfect attachment of the ends of the beams to the side of the ship, and the want of connexion between beam and beam and the longitudinal one, by the weights placed in the body in no degree corresponding with the displace ment of water at the several sections. it is the ob ject of Sir Robert Seppings to prevent these changes in figure by constructing ships according to a new ap plication of matter, by which the strains to which they arc subject shall be more equally divided through out the fabric, and the material placed in such direc tions as are best adapted to resist those forces; and also by a new combination of the parts of their frames, so as to be enabled to bring into use timber which, from form, its smaller size and less length, shall be more easy to be obtained, and therefore less expen sive. These improvements have been completely successful, and on this subject, we cannot do better than quote the opinion of a select committee of the House of Commons, which is given in their third report on Finance.
'• Your committee deem it their duty particularly to notice Mr. Seppings, one of the surveyors of the navy, to w hose abilities and exertions the country is mainly indebted for many of its most valuable im provements in naval architecture; the ingenious mo dels of which have been submitted to the inspection of your committee, with all the necessary explanations of their several uses and application. Your commit tee do not pretend to describe or appreciate with ac curacy the value of these improvements, to estimate which to their full extent, requires considerable pro fessional experience; they are, however, fully con vinced, that the result of them will he to effectuate, in the construction of ships of war, a great saving of expenditure to the public, and to secure a proportion ate economy of human life, arising from their superior durability, and the great power of resistance to the elements, and to the casualties incidental to nautical life, which the modern system of keeping our ships at sea, at all seasons, and in all weathers, has rendered of the utmost importance. These services, although
they have nothing of that brilliancy which forcibly attracts public admiration, will continue to confer a lasting benefit to the British nation lung after that period when the beneficial effects of victories, how ever splendid, shall have passed away."* As the arching of ships has been considered in all times as their most serious defect, it has been the ob ject of maritime nations to take measures to prevent it; and we find that some of the ablest mathematicians and engineers have turned their attention to this ob ject, and that their views have been for the most part the same, that of placing some of the materials in a diagonal direction, that the forces may act in the di rection of their fibres, either by pulling or pressing upon them, the strongest direction in which materials of metal or wood can be placed. The mode of ap plication in each case has differed according to the notions of the projector. These plans, however, have been severally abandoned after sufficient trial, and the causes assigned were the want of abutments; they are detailed with much ingeniousness by the Baron Dupin in his paper before quoted.
It remained for the genius of Seppings to adapt successfully the laying of the materials diagonally in shipbuilding to a considerable extent, and by a new and happy combination, by substituting the triangle for the rectangle, to effect the purpose so long desired. On which plans (Plate CCCCXCV1I1. Fig. 1.) all ships and vessels belonging to our navy are now con structed; nor has it been confined to this country, for the advantages being so apparent, those ships of war which have been recently built by most foreign powers have also been constructed thereby. The arching of ships at the present time is comparatively nothing. and there are many instances of vessels built accord ing to this method, having been saved, which would inevitably have been lost had they been constructed according to the method formerly practised.