MECHANICS AND USEFUL ARTS. 31 



be kept up, and a greater number, as regards the speed of a boat, are 

 positively injurious. In most of our vessels, the paddles are much 

 too numerous, there often being 28 and 32, which are sometimes in a 

 manner split, and thus doubled in number. The Cherokee (Chagres 

 steamer) has six blades below the surface when ready for sea. The 

 Washington has five fully immersed on each side. A boat never pro- 

 gresses in the ratio of the revolutions of the wheels, because of the 

 yielding nature of the medium in which they act. Thus in going from 

 New York to Liverpool, a distance of 3,023 miles, the paddles of the 

 ocean steamers pass over a distance varying from 5,000 to 8,000 miles. 

 This can be in a measure modified by giving the paddles a better hold 

 of the fluid they sweep through, and Mr. Ewbank recommends various 

 forms for them ; but the principle in general is, that as the propelling 

 power of the paddle is greatest at its lower or outer extremity, and 

 diminishes to nothing at the surface, so its face should enlarge witli 

 the dip and be nothing or very small above. Thus the common forms 

 of paddles are seen to be entirely wrong, and the best form would be 

 triangular, as is the case with the tails of fishes and the webbed feet 

 of the sea-swimming birds. The propelling virtue of blades expands 

 and contracts with their thickness, it being greatest when they are 

 reduced to the thinnest plates consistent with the strains they must 

 oppose, so that metallic plates will probably soon be substituted for 

 the thick wood planks. Again, the sharper the dipping edges of the 

 paddles are made, the more back water they throw off at the point 

 where its departure is most beneficial, so that here again metal has 

 the advantage. The sharp edges in paddles are similar in their nature 

 to the mere film which forms the tails of fishes. 



It has been usual to assert that the thicker the paddles the better, 

 because they do no harm, and add to the weight of the wheels, so as 

 to make their motions more uniform ; and acting on this view, our 

 steamers have had their paddles made of plank from 1 to 3 inches 

 in thickness. In the Cunard steamers they are 2 inches, in the 

 Franklin, of the Bremen line, 2.}, and in others, such as the Atlantic 

 and Pacific, of the Collins (Liverpool) line, they are to be 3 inches. 

 In the Atlantic, the paddles, if united, would form a solid mass 7 

 feet thick, equal to one fifth of the diameter of the wheel. They 

 are to be 12 feet long by 34 inches, so that they contain nearly 500 

 cubic feet of timber, and at every revolution they must displace this 

 enormous body of water by their submersion alone, not only use- 

 lessly, but with a serious retardation of the vessel's headway. In the 

 Pacific, the loss is even greater, and in every revolution of each 

 wheel her paddles will lose 7^ feet of effective stroke, to the 7 feet 

 loss of the Atlantic. In like manner, the loss in the wheels of the 

 United States is from 10 to 15 feet of the effective stroke in every 

 revolution. It can easily be seen what a saving would be effected by 

 using -inch iron instead of 3-inch plank. Plates of steel are the 

 best material, combining strength and thinness. A great loss in the 

 power of the paddles is caused by having projections, such as bolts, 

 nuts, stays, &c., on their faces. If any material could be found which 

 would durably prevent the paddles from becoming wetted, they would 



