The steam engine familiarly explained and illustrated; with an historical sketch of its invention and progressive improvement; its applications to navigation and railways; with plain maxims for railway speculators. By the Rev. Dionysius Lardner ... With additions and notes by James Renwick ...

STEAM NAVIGATION. 257
than are now attainable; or, finally, with the same tonnage
and the same lading, they may be supplied with more powerful machinery.
(117.) To obtain from the moving power its full amount of
mechanical effect in propelling the vessel, it would be necessary that its force should propel, by constantly acting against
the water in a horizontal direction, and with a motion contrary to the course of the vessel. No system of mechanical
propellers has, however, yet been contrived capable of perfectly attaining this end. Patents have been granted for
many ingenious mechanical combinations to impart to the
propelling surfaces such angles as appeared to the respective
contrivers most advantageous. In most of these, however,
the mechanical complexity has formed a fatal objection. No
part of the machinery of a steam vessel is so liable to become
deranged at sea as the paddle wheels; and, therefore, such
simplicity of construction as is compatible with those repairs
which are possible on such emergencies is quite essential for
safe practical use.
The ordinary paddle wheel, as I have already stated, is a
wheel revolving upon a shaft driven by the engine, and carrying upon its circumference a number of flat boards, called
paddle boards, which are secured by nuts or braces in a fixed
position; and that position is such that the planes of the pad
die boards diverge nearly from the centre of the shaft on
which the wheel turns. The consequence of this arrangement is that each paddle board can only act in that direction
which is most advantageous for the propulsion of the vessel
when it arrives near the lowest point of the wheel. In
by the increased economy of fuel will not be in so great a proportion as the
saving of fuel. A quantity of fuel of equivalent power will occupy about half
the present space, but the displacement or immersion which it produces will be
only one-fourth of its present effect.
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