The Evolution of the Screw Propeller

From Paddle Wheels to Sailing Ships & Steam Ships

by Nick Baker

Early Screws

The word propeller conjures images of helicopters, beanie hats, and toy boats. However, in the early 1800s propellers generally meant paddle-wheels. That began to change with the launch of the Archimedes in May of 1839. The ship was unique in an age of paddle-wheel steamers. The Archimedes was steam powered, but was not propelled by paddle-wheels. Instead, she was fitted with a device described to the patent office as "an improved propeller" in the shape of "a sort of screw, or worm." The Archimedes was only the first in a series of practical screw-propelled ships. Within four years, the screw had been deemed equal if not superior to paddle-wheels. Its success led to several articles concerning the Archimedes and the screw in general in the Journal of the Franklin Institute in 1844. These articles sought to describe the new device to the reader, as well as determine possible strengths, weaknesses, and potentials of the screw. Embedded in the language of the articles are signs of the attitudes towards mechanization and the transformation from wind to steam power.

Figure 1

One major difference between the screw and the paddle-wheel was its placement. In the Archimedes, the screw was placed in the rear of the ship well below the water line. In Figure 1, its placement in the dead wood and its original shape can be seen. By dividing the single turn into half or quarter turns, the screw was made shorter, as in Figures 2 and 3. By these divisions, the Archimedes' screw was refined until it resembled a modern propeller. Most readers were unacquainted with the wake of a screw-driven ship, so that the author felt compelled to give a description of it. "On starting the vessel in a dead calm, a column of water in the shape of an inverted cone may be seen thrown astern of the ship, from which it is inferred that the whole force of the screw is propellant in the direct line of its axis." (91) Anyone who has been in a motor boat is familiar with the wake he describes, but at the time it aroused curiosity. This description implies a varied audience which would be interested in more than simply technical aspects of the new invention.

Figure 2

Figure 3

The theory behind screw propulsion was difficult for people to comprehend. Until the 1840s, the primary means of using steam power to propel a ship was with paddle-wheels. The concept behind this was easily understandable. Paddles, like oars, were attached to wheels, and simply pushed a boat through the water as if it were being rowed. The screw, on the other hand, was an unfamiliar means of propelling a ship. This is evidenced by the way screws are referred to in early patent applications. One patent from 1824 describes a screw as a "revolving oar." (95) Two years later, someone patented "improvements in wheels and paddles for propelling boats," which consisted of a "spiral paddle." (95) Another patent lists "sculling wheels, or screw propelling wheels." (96) All of these accounts display a certain difficulty in describing a novel object. The horseless carriage is a similar example. In both cases, the new invention must be referred to in the terminology of the artifact which it has rendered obsolete.

The screw was not immediately appealing to most people. This was evidenced when the British government built two sister ships, the Rattler and the Prometheus, in order to test the effectiveness of the screw. The Rattler was fitted with a screw, but the Prometheus with traditional paddle-wheels. The two ships were then put through time trials.

"Under these circumstances more than ordinary interest was excited amongst the naval and engineering officers connected with the Woolwich Dockyard establishment, by whom the results of the various trials of both vessels were most minutely noted, and, in the end, summed up, contrary to the general expectation, in favor of the Rattler..." (368, my italics)

The men who designed and built the ships had expected paddle-wheels to prevail. These men thought of propulsion in terms of oar-like propellers. These preconceptions likely led to a difficulty in conceptualizing the means by which the screw exercised its motive power, and thus an expectation of failure.

The author notes several aspects of the screw which make a screw-propelled ship more sea-worthy and thus superior to paddle-wheels. "One great advantage of the screw being placed [in the keel] is, the transferring the whole weight of the propelling apparatus from the top sides of a vessel to the lowest part of the hull."(91) This transfer of weight lowers the center of gravity, making the vessel less inclined to pitch and roll. Also, in a heavy sea, paddle-wheels become less effective. As the ship lists to one side or the other, one wheel will be submerged while the other is lifted out of the water. In a truly violent storm, paddle-wheels may even be broken by the action of the waves against the boards. The author praises the screw, as it suffers from no similar deficiencies.

As a result of these advantages, the Archimedes proved to be a surprisingly fast ship. In April of 1840, she set a new speed record for the trip from Dover to Calais. Despite this, the author notes that the Archimedes was "not built for extreme speed, but more to show the practicability of uniting sailing and steaming qualities in one vessel, [and] has succeeded in beating many vessels of superior power, built expressly for steaming." (93) This combination was also made explicit in the drawing at right. The ship which is shown in the picture looks more like a wooden sailing ship than a steamer, and thereby implies a unification of wind and steam power. Apparently, a combination of steam and sails was seen as superior to steam alone. Steam ships had been in existence for less than thirty years, and most of these carried some rigging in addition to their paddle-wheels. However, under sail a ship lists considerably, rendering paddle-boxes ineffective means of propulsion, as one is submerged while the other is dry. Furthermore, the submerged paddle-wheel will act as a drag, slowing the ship considerably and causing it to veer to leeward. By placing the screw well below the water line, the Archimedes suffered no such difficulties, and was thus able to take advantage of steam and sails simultaneously or individually. Steam power could be used as a complement to, rather than a replacement of, wind power.

The author makes another point concerning the value of combining steam and sails. Noting that under sail the vessel travels almost as fast as under steam, he says, "...the expenditure of fuel need not be resorted to during favorable winds... Upon twenty out of thirty-two points of the compass a ship would be able to dispense with her steam power altogether." (94) Once again the supplementary nature of steam power is asserted. Certainly, longer voyages could be made with less fuel if wind power were employed. Also, the increased efficiency would reduce dependence on coaling stations. Another benefit is voiced by a Captain Hosken, who stated that,

"...in his opinion, as a naval officer, one of the great merits of the screw as a propeller, was its capability of being adapted to a full-rigged ship, using at times her canvas as usual. The British seamen would thus be fully as much employed as heretofore, and they would retain that superiority which had so largely contributed to the high position held by Great Britain in the scale of nations." (Vol. XI, 84)

The mechanization of ships had necessarily displaced many sailors whose skill with rigging and sails was rendered obsolete. For this officer, the screw represented the possibility of reversing the effects of the displacement with a return to fully rigged ships, thereby helping the British maintain their superiority. Implicit in that statement is that steam power somehow degrades sailors, which reveals a questioning of the moral effects of mechanization similar to the debate in America over factories.

Sailing ships could be becalmed, but early steam ships were not significantly faster than sailing ships. Further, steamers were limited by their fuel needs and were subject to mechanical failure. Until steam engines could reliably provide greater speed than the fastest sailing ship, sails would not be dispensed with. Perhaps the preference for a hybrid of steam and wind power was a sign of the larger transformation going on at the time. This transformation was part of a shift from the power of wind and water to that of coal and steam. The change to steam power was not linear, as sails were largely given up on paddle-wheel ships, and then reintroduced on screw-propelled vessels. While people may have embraced the changes, some had reservations about mechanization in general. It is clear from these articles that for a time, in the case of shipping at least, one form of power was not demonstrably superior to the other. It was not clear which power source or combination would prevail, and this ambiguity was reflected in the rhetoric of the time.

Thomas P. Jones, ed. The Journal of the Franklin Institute. The Franklin Institute, Philadelphia: 1844. All parenthetical citations are from the Third Series, Volume VII, except as noted.