This invention is intended for propelling light vessels at a high velocity on canals. It consists in a novel and ingenious application of the converse principle of the arrangement commonly known as the Chinese or differential crane, the latter being designed to move a great load through a small space, by a small force moving through a large space; whilst in this invention a small load is moved through a large space, by means of a great force moving through a small space.
In order that the invention may be fully understood, it will be necessary to explain clearly the principle of it, before we describe the practical application. It is thus explained in the specification, which is given at length in the Repository of Arts.
Fig. 1 represents a combination of two pulleys, their diameters being as six to seven; a being the larger pulley, and b the smaller one; c d is an endless rope, passing over the sheaves e e, which rope it should be observed takes a turn round each of the pulleys a and b, that is to say, the part c taking a turn round the larger pulley a, and the part d taking a turn round the smaller pulley b. If then the rope d be caused to move in the direction of the arrow, it will have a tendency to draw the lower part of the pulley b in the same direction; while the part c of the endless rope will be moving in an opposite direction, and will have a tendency to move the lower part of the pulley a in the same direction; consequently, the two pulleys a b (they being fixed together) would turn on the mean point f, as a fulcrum; g is the centre of the two pulleys. Let it then be supposed, that the part d of the endless rope be moved from h to i, it will be evident that the centre g of the differential pulleys a b, would be moved to the point j; and consequently if any object were connected to the centre g of these differential pulleys, it would be propelled from g to j by the endless rope being moved the much smaller distance of h to i, as is clearly indicated by the dotted lines; and these distances will be as thirteen to one.
We shall now describe the mechanical arrangement of the invention, as applied to propel vessels on canals.
a and b are two pulleys upon one axis c, the points of which turn in holes in the forked frame d, the stem of which (e,) turns in sockets g g, at the outer extremity of the arm h. The pulley a is fixed to the axis, but the pulley b is loose upon the axis; k is a sliding clutch upon the axis, carrying an arm m, in which is a pin passing through a hole in one of the arms of the pulley a; n is a bent lever turning upon a pin in the forked frame d, and having a forked extremity, which embraces the sliding clutch k. When by the motion of the lever the clutch is brought close to the pulley a, the pin in the arm m passes between the spokes of the pulley b; and when it comes in contact with one of them, it carries the pulley round with the pulley a, and the machine is then in gear. The opposite motion of the lever withdraws the pin, and the pulleys are free to revolve in opposite directions, and the operation of the machine is suspended.
The apparatus above described is supported over the side of the vessel by a vertical standard, which supports the arm h in a horizontal position; and the endless ropes are passed round the pulleys, as described, and through two riggers, placed one at each end of the canal. If power be applied to draw the rope by any method, as for instance, by means of a steam engine applied to turn one of the riggers, the vessel to which the apparatus is attached will be propelled, with a velocity which will be to that of the rope, as it passes over the rigger, in the ratio of the sum of the diameter of the pulleys, to their difference; thus if the diameters be as 8 to 9, the velocity will be as 17 to 1; and if the rigger turn with a speed of 2 miles per hour, the boat will be drawn at the rate of 34 miles per hour.
The rope must be supported upon rollers, placed along the banks of the canal, in order that it may run light; and the object of making the stem of the fork d turn in the sockets g g, is to allow the pulleys a and b to stand at an angle, by which the endless rope may be led into the sheaves when the carriage is going in a curved direction.