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. 26:9
on the supposition that the immersed part of the floating.body remains the same. Now I have myself proved by
experiments on canals, that when the speed of the boat is
increased beyond a certain limit, its draught of water is
rapidly diminished; and in the case of a large steam raft
constructed upon the river Hudson, it was found that when
the speed was raised to 20 miles an hour, the draught of water
-was diminished by 7 inches. I have therefore no doubt
that the increased speed of steamers is attended with a like
effect:; that, in fact, they rise out of the water; so that, although the resistance is increased by reason of their increased
speed, it is diminished in a still greater proportion by reason
of their diminished immersion.
Meanwhile, whatever be the cause, it is quite certain that
the resistance in moving through the water must be diminished, because the moving power is always in proportion to
the quantity of coals consumed, and at the same time in the
proportion to the resistance overcome.. Since, then, the
quantity of coals consumed in a given distance is diminished
while the speed is increased, the resistance encountered
throughout the same distance must be proportionally diminished.
(122.) Increased facility in the extension and application
of steam navigation is expected to arise from the substitution
of iron for wood, in the construction.of vessels. Hitherto
iron steamers have been chiefly confined to river navigation;
but there appears no sufficient reason why their use should
be thus limited. For sea voyages they offer many advantages; they are not half the weight of vessels of equal tonnage constructed of wood; and, consequently, with the
same tonnage they will have less draught of water, and
therefore less resistance to the propelling power; or, with
the same draught of water and the same resistance, they
will carry a proportionally heavier cargo. The nature of
their material renders them more stiff and unyielding than
timber;- and. they do not: suffer that effect which is called hog
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