Form and Proportions. - Resistance. - Beaufoy's Experiments. - Russell's Experiments. - Remarkable deviations from the assumed law of velocity.- "The solitary wave of progression" not dependent upon form or velocity, but upon the depth of the fluid. - Mr. Houston's accidental discovery of a diminution of resistance at certain increased velocities of motion. - Form of vessel of least resistance. - The "Wave"- lines of. - Sir J. Robison's Experiments. - Mr. Oldham's suggestion for improved experi mental apparatus. - Tables showing results of experiments. - Proportion of power to tonnage or admeasurement. - Velocity of the great American steam raft. - Approximate Tables of tonnage, power, and consumption of fuel. - Mr. Morgan's assignment of due proportion of power to tonnage. - Dimensions of several Government steam packets. - Specification for constructing a 600 ton steam packet. - Diagrams of. - Separate water-tight iron bulkheads. - Mr. Lang's method of Diagonal Planking. - Iron vessels - advantages of. - Dimensions of the iron steam boat "Alburkah." - Construction and dimensions of the hull and machinery of the great iron steam ship, " Great Britain." - Twin boats. - The great American steam raft. - Snodgrass's twin boats. - Gemmel's twin boats.
In proceeding to describe the form and construction of steam boats, we shall commence by noticing the points in which they most differ from sailing vessels. As the wind is generally more or less oblique to a vessel's course, or directed against the side of the vessel, and as the centre of effort of the sails in a ship is at a considerable height above the longitudinal axis of rotation, the wind acts with considerable leverage upon the sails and masts, to cause the ship to heel, or incline over to one side: to counteract this, and impart sufficient lateral stability, or stiffness, the breadth of sailing vessels requires to bear a greater proportion to the length than is necessary in steam vessels: the whole of the impelling force in the latter being exerted in the line of the vessel's course. Sailing vessels likewise require to be of greater comparative depth than steamers, to prevent their being driven laterally out of their course, (or to leeward, as it is termed,) when the wind is contrary; steamers being capable of proceeding directly head to wind, the point to be chiefly attended to is, that the form of the hull be such as to oppose the least resistance to its direct progress; and as the resistance depends chiefly upon the area of the immersed transverse section, their breadth and depth are generally considerably less than that of sailing vessels of the same tonnage, and the requisite capacity is obtained by a proportionate increase of length; thus, whilst in sailing vessels the breadth is rarely less than one-fourth of the length, in steam vessels it is frequently only one-seventh. Other advantages likewise result from this change in the proportions: steam vessels being employed chiefly as coasters, their light draught of water enables them to enter harbours which would otherwise be inaccessible to them.
Their increased length also assists in preserving their parallelism, upon which their velocity greatly depends; and, as they do not pitch so suddenly nor so deeply in heavy seas, they hold their way better, and the hull and machinery are less strained. Their increased length likewise affords greater accommodation for passengers, which is a very great advantage.