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ON THE ARCHIMEDEAN SCREW,
OR SUBMARINE PROPELLER.
In the original text of Mr. Tredgold, as well as in the Appendix by subsequent
writers, the investigations respecting the method of propelling steam vessels have
been chiefly confined to the paddle wheel. Mr. Tredgold, indeed, slightly adverts
to the subject of screw propellers, giving algebraic calculations of some of their
properties, and concludes by recommending the matter to the reader’s considera
tion. Since that period, however, the inquiry has assumed a considerable degree of
importance, by its becoming the subject of extensive and careful experiments; and
the results having induced the British and French Governments to determine on
the adoption of this method of propelling some of their vessels, no Work on
Steam Navigation can be considered complete without ample reference to the
subject, and such investigation of the properties and comparative efficacy of the
system as the data of an infant invention will furnish.
Screw propellers, however variously they may be modified, all derive their
power of propelling by being placed on an axis which is parallel to the keel, and
by having threads or blades extending from the axis, which form segments of a
helix or spiral, 1 so that, by causing the axis to revolve, the threads worm their
way through the water much in the same way as a carpenter’s screw inserts
itself into a piece of wood.
There is this distinguishing difference, however, between the action of a
carpenter’s screw and of the screw propeller, namely, that the latter, acting
upon a fluid, cannot propel the vessel without causing the water to recede, while
the carpenter’s screw progresses through the wood without any such recession.
1 The terms screw and spiral are frequently confounded. They constitute, however, distinct forms.
The screw is an inclined plane wound round a cylinder, and the spiral an inclined plane wound round a
cone or spire.
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