SCREW AND PADDLES COMBINED.
613. Q.--Would not a screw combined with paddles act in a similarly advantageous way as a screw or paddles when aided by the wind?
A.--If in any given paddle vessel a supplementary screw be added to increase her power and speed, the screw will act in a more beneficial manner than if it had the whole vessel to propel itself, and for a like reason the paddles will act in a more beneficial manner. There will be less slip both upon the paddles and upon the screw than if either had been employed alone; but the same object would be attained by giving the vessel larger paddles or a larger screw.
614. Q.--Have any vessels been constructed with combined screw and paddles?
A.--Not any that I know of, except the great vessel built under the direction of Mr. Brunel. The Bee many years since was fitted with both screw and paddles, but this was for the purpose of ascertaining the relative efficiency of the two modes of propulsion, and not for the purpose of using both together.
615. Q.--What would be the best means of accelerating the speed of a paddle vessel by the introduction of a supplementary screw?
A.--If the vessel requires new boilers, the best course of procedure would be to work a single engine giving motion to the screw with high pressure steam, and to let the waste steam from the high pressure engine work the paddle engines. In this way the power might be doubled without any increased expenditure of fuel per hour, and there would be a diminished expenditure per voyage in the proportion of the increased speed.
616. Q.--What would the increased speed be by doubling the power?
A.--The increase would be in the proportion of the cube root of 1 to the cube root of 2, or it would be 1.25 times greater. If, therefore, the existing speed were 10 miles, it would be increased to 12-1/2 miles by doubling the power, and the vessel would ply with about a fourth less coals by increasing the power in the manner suggested.
617. Q.--Is not high pressure steam dangerous in steam vessels?