SHIP building. The man of science and the practical shipwright have long la mented, that in the theory of the art of shipbuilding there are so few fixed and positive principles established by demon stration, or confirmed by practice ; thus the artist, being left to the exercise of his own opinion, in general resists theoreti cal propositions, however founded, so hard has it ever been found to overcome habitual prejudices.
The great neglect of the theory of ship-building is much to be deplored in a country like this, where the practical part is so well understood and executed. Mathematics, engineering, and civil or house architect, are sciences nourished and taught in our universities and other schools, and however superior scholars may arrive in those arts, and celebrated for their abilities, show them shipping draughts, or talk to them of the science of ship-building, and they appear as much at a loss as though they had never heard of such an art ; nevertheless, it may be but justice to add, that some men of dif ferent professions have felt themselves interested in its progress to perfection, and lately we have seen the endeavours of men conversant in the practical parts of ship-building, publishing their ideas, and this in hopes that gentlemen of more scientific abilities may be induced to add to their labours, and make the theory of ship-building much more familiar in this country, as few, very few, professional shipwrights have hitherto had it in their power to employ their talents to improve this science by theory.
Ships are bodies, which, when to be put have water for their resisting force, and a contrary element, as air or wind for their impelling force : therefore the theorist and practical ship-builder should ever keep particularly in view to improve himself in the knowledge of floating bodies, and endeavour to gain a complete knowledge of the resistance of fluids ; add to this aerostatics and mathe matics in general. Thus taught, the man of practice would, though cautiously, add the speculation of the theorist, as there is a great deal to be risked, and much to be suffered ; but could the ideas of the theorist and the man of practice be assi milated and well weighed together, much benefit to the art of ship-building might be acquired, and their most useful ideas be reduced to the test of experiment.
When experience favours theory, then we arrive at the desired point ; but the difficulty and expense of accurately mak ing a sufficient number of experiments is a great hindrance to its assumption, and has greatly hindered that desired knowledge in this branch of science. Notwithstanding these obstacles, many opportunities offer of introducing well digested theory, though cautiously and by degrees, into the many various ships and vessels building in this kingdom ; and thus we would hope, by the united ef forts of the theorist, ship-builder, and mariner, who should carefully notice and report every observation in his power of the vessel acting in her various situations, that the different results being accurate ly stated, desirable data may be reason ably established.
It is well known that bodies of any magnitude could not be built or put to gether without designs or drawings on convenient scales, particularly that com plex machine a ship ; therefore an accu rate delineation of the whole vessel, with respect to its various lengths, heights, breadths. and depths, is carefully repre sented by a drawing, called the sheer draught, the construction of which, with its several lines, &c. we shall endeavour as familiarly as possible to describe to our readers.
The principal dimensions as they are generally termed, must be first decided upon, and they are the following, viz.
The length at the gun-deck in ships of war, or distance between the extreme perpendiculars in merchant ships.
The extreme breadth, which is the thickness of the bottom plank on each side, added to the moulded breadth, or broadest part of the ship in midships.