Even that most modern mercantile vessel known as the “whale-back” with its nearly flat bottom, vertical sides, arched top or deck, skegged or spoon-shaped at bow and stern, straight deck lines, the upper deck cabins and steering gear raised on hollow turrets, with machinery and cargo in the main hull, has not departed much from the safe rule of proportions of its ancient prototype. But in other respects the ideas of Noah and of the Phœnicians, the best of ancient ship-builders, as well as the Northmen, the Dutch, the French, and the English, the best ship-builders of later centuries, were decidedly improved upon by the Americans, who, as above intimated, were revolutionizing the art and building the finest vessels in the early part of the century, and these rivalled in speed the steam vessels for some years after steamships were ploughing the rivers and the ocean. Discarding the lofty decks fore and aft and ponderous topsides, the principal characteristics of the American “clippers” were their fine sharp lines, built long and low, broad of beam before the centre, sharp above the water, and deep aft. A typical vessel of this sort was the clipper ship _Great Republic_, built by Donald McKay of Boston during the first half of the century. She was 325 feet long, 53 feet wide, 37 feet deep, with a capacity of about 4000 tons. She had four masts, each provided with a lightning rod. A single suit of her sails consisted of 15,563 yards of canvas. Her keel rose for 60 feet forward, gradually curved into the arc of a circle as it blended with the stern. Vessels of her type ran seventeen and eighteen miles an hour at a time when steam vessels were making only twelve or fourteen miles an hour, the latter speed being one which it was predicted by naval engineers could not with safety be exceeded with ocean steamships. These vessels directed the attention of ship-builders to two prominent features, the shape of the bow and the length of the vessel. For the old convex form of bow and stern, the principal of an elongated wedge was substituted, the wedge slightly hollowed on its face, by which the waters were more easily parted and thrown aside. A departure was early made in the matter of strengthening the “ribs of oak” to better meet the strains from the rough seas. In 1810 Sir Robert Seppings, surveyor of the English navy, devised and introduced the system of diagonal bracing. This was an arrangement of timbers crossing the ribs on the inside of the ship at angles of about 45°, and braced by diagonals and struts.