- Shopping Bag ( 0 items )
Both Archimedes (c. 250 BC) and Leonardo da Vinci (c.1500) can be credited with having considered designs and ideas which would subsequently be explored by ship propulsion engineers many years later. In the case of Archimedes, his thinking centered on the application of the screw pump which bears his name and this provided considerable inspiration to the nineteenth-century engineers involved in marine propulsion. Unfortunately, however, it also gave rise to several subsequent misconceptions about the basis of propeller action by comparing it to that of a screw thread. In contrast Leonardo da Vinci, in his sketchbooks which were produced some 1700 years after Archimedes, shows an alternative form of screw propulsion based on the idea of using fan blades having a similar appearance to those used for cooling purposes today.
The development of screw propulsion as we recognize it today can be traced back to the work of Robert Hooke, who is perhaps better remembered for his work on the elasticity of materials. Hooke in his Philosophical Collections, presented to the Royal Society in 1681, explained the design of a horizontal watermill which was remarkably similar in its principle of operation to the Kirsten-Boeing vertical axis propeller developed two and a half centuries later. Returning however to Hooke's watermill, it comprised six wooden vanes, geared to a central shaft and pinned vertically to a horizontal circular rotor. The gearing constrained the vanes to rotate through 180° about their own spindle axes for each complete revolution of the rotor.
During his life Hooke was also interested in the subject of metrology and in the course of his work he developed an air flow meter based on the principle of a windmill. He successfully modified this instrument in 1683 to measure water currents and then foresaw the potential of this invention to drive ships through the water if provided with a suitable means of motive power. As seen in Figure 1.1 the instrument comprises four, flat rectangular blades located on radial arms with the blades inclined to the plane of rotation.
Some years later in 1752, the Académie des Sciences in Paris offered a series of prizes for research into theoretical methods leading to significant developments in naval architecture. As might be expected, the famous mathematicians and scientists of Europe were attracted by this offer and names such as d'Alembert, Euler and Bernoulli appear in the contributions. Bernoulli's contribution, for which he won a prize, introduced the propeller wheel, shown in Figure 1.2, which he intended to be driven by a Newcomen steam engine. With this arrangement he calculated that a particular ship could be propelled at just under 2½ knots by the application of some 20–25 hp. Opinion, however, was still divided as to the most suitable propulsor configuration, as indeed it was to be for many years to come. For example, the French mathematician Paucton, working at about the same time as Bernoulli, suggested a different approach, illustrated in Figure 1.3, which was based on the Archimedean screw.
Thirty-three years after the Paris invitation Joseph Bramah in England proposed an arrangement for a screw propeller located at the stern of a vessel which, as may be seen from Figure 1.4, contains most of the features that we associate with screw propulsion today. It comprises a propeller with a small number of blades driven by a horizontal shaft which passes into the hull below the waterline. There appears, however, to be no evidence of any trials of a propeller of this kind being fitted to a ship and driven by a steam engine. Subsequently, in 1802 Edward Shorter used a variation of Bramah's idea to assist sailing vessels that were becalmed to make some headway. In Shorter's proposal, Figure 1.5, the shaft was designed to pass into the vessel's hull above the waterline and consequently eliminated the need for seals; the motive power for this propulsion arrangement was provided by eight men at a capstan. Using this technique Shorter managed to propel the transport ship Doncaster in Gibraltar and again at Malta at a speed of 1.5 mph in calm conditions: perhaps understandably, in view of the means of providing power, no further application of Shorter's propeller was recorded, but he recognized that this propulsion concept could be driven by a steam engine. Nevertheless, it is interesting to note the enthusiasm with which this propeller was received by Admiral Sir Richard Rickerton and his Captains (Figure 1.6).
Colonel John Stevens, who was a lawyer in the USA and a man of substantial financial means, experimented with screw propulsion in the year following Shorter's proposal. As a basis for his work he built a 25 ft long boat into which he installed a rotary steam engine and coupled this directly to a four-bladed propeller. The blades of this propeller were flat iron plates riveted to forgings which formed a 'spider-like' boss attachment to the shaft. Stevens later replaced the rotary engine with a steam engine of the Watt type and managed to attain a steady cruising speed of 4 mph with some occasional surges of up to 8 mph. However, he was not impressed with the overall performance of his craft and decided to turn his attention and energies to other means of marine propulsion.
In 1824 contra-rotating propellers made their appearance in France in a design produced by Monsieur Dollman. He used a two-bladed set of windmill type propellers rotating in opposite directions on the same shaft axis to propel a small craft. Following on from this French development the scene turned once again to England, where John Ericsson, a former Swedish army officer residing at that time in London, designed and patented in 1836 a propulsion system comprising two contra-rotating propeller wheels. His design is shown in Figure 1.7, from which it can be seen that the individual wheels were not dissimilar in outline to Bernoulli's earlier proposal. Each wheel comprised eight short, wide blades of a helical configuration mounted on a blade ring with the blades tied at their tips by a peripheral strap. In this arrangement the two wheels were allowed to rotate at different speeds, probably to overcome the problem of the different flow configurations induced in the forward and after wheels. Ericsson conducted his early trials on a 3 ft model, and the results proved successful enough to encourage him to construct a 45 ft vessel which he named the Francis B. Ogden. This vessel was fitted with his propulsion system and had blade wheels with a diameter of 5 ft 2 in. Trials were conducted on the Thames in the presence of representatives from the Admiralty and the vessel was observed to be capable of a speed of some 10 mph. However, in his first design Ericsson placed the propeller astern of the rudder and this had an adverse effect both on the steerability of the ship and also on the flow into the propeller. The Admiralty Board expressed disappointment with the trial although the propulsion results were good when judged by the standards of the day. However, it was said that one reason was their concern over a vessel's ability to steer reliably when propelled from the stern. Following this rebuff Ericsson left England for the USA and in 1843 designed the US Navy's first screw-propelled vessel, the Princeton. It has been suggested that by around this time the US merchant marine had some forty-one screw-propelled vessels in operation.
The development of the screw propeller depended not only on technical development but also upon the availability of finance, politics and the likely return on the investment made by the inventor or his backers. Smith was rather more successful in these respects than his contemporary Ericsson. Francis Petit Smith took out a patent in which a different form of propeller was used, more akin to an Archimedean screw, but, more importantly, based on a different location of the propeller with respect to the rudder. This happened just a few weeks prior to Ericsson establishing his patent and the British Admiralty modified their view of screw propulsion shortly after Ericsson's trials due to Smith's work. Smith, who despite being frequently referred to as a farmer had a sound classical education, explored the concepts of marine propulsion by making model boats and testing them on a pond. From one such model, which was propelled by an Archimedean screw, he was sufficiently encouraged to build a six tonne prototype boat, the F P Smith, powered by a 6 hp steam engine to which he fitted a wooden Archimedean screw of two turns. The vessel underwent trials on the Paddington Canal in 1837; however, by one of those fortunate accidents which sometimes occur in the history of science and technology, the propeller was damaged during the trials and about half of it broke off, whereupon the vessel immediately increased its speed. Smith recognized the implications of this accident and modified the propeller accordingly. After completing the calm water trials he took the vessel on a voyage down the River Thames from Blackwall in a series of stages to Folkestone and eventually on to Hythe on the Kentish coast: between these last two ports the vessel averaged a speed of some 7 mph. On the return voyage to London, Smith encountered a storm in the Thames Estuary and the little craft apparently performed excellently in these adverse conditions. In March 1830 Smith and his backers, Wright and the Rennie brothers, made an approach to the Admiralty, who then requested a special trial for their inspection. The Navy's response to these trials was sufficiently encouraging to motivate Smith and his backers into constructing a larger ship of 237 tonnes displacement which he called Archimedes. This vessel, which was laid down by Henry Wilmshurst and engined by George Rennie, was completed in 1839. It had a length of 125 ft and was rigged as a three-masted schooner. The Archimedes was completed just as the ill-fated Screw Propeller Company was incorporated as a joint stock company. The objectives of this company were to purchase Smith's patents, transfer the financial interest to the company and sell licenses to use the location for the propeller within the deadwood of a ship as suggested by Smith, but not the propeller design itself. The Archimedes was powered by two 45 hp engines and finally fitted with a single turn Archimedean screw which had a diameter of 5 ft 9 in., a pitch of 10 ft and was about 5 ft in length. This propeller was the last of a series tried on the ship, the first having a diameter of 7 ft with a pitch of 8 ft and a helix making one complete turn. This propeller was subsequently replaced by a modification in which double-threaded screws, each of half a turn, were employed in accordance with Smith's amended patent of 1839. The propeller is shown in Figure 1.8. After undergoing a series of proving trials in which the speed achieved was in excess of nine knots the ship arrived at Dover in 1840 to undertake a series of races against the cross-channel packets, which at that time were operated by the Royal Navy. The Admiralty was duly impressed with the results of these races and agreed to the adoption of screw propulsion in the Navy. In the meantime, the Archimedes was lent to Brunel, who fitted her with a series of propellers having different forms.
Excerpted from Marine Propellers and Propulsion by J S Carlton Copyright © 2012 by John Carlton. Excerpted by permission of Butterworth-Heinemann. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.