188 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[May, 



of 1 foot square was equivalent to the midship section of the vessel, of which 

 the mobilities were from -^th to ^':jth. There could be no doubt, that the im- 

 provements in the forms of the modern vessels, would have produced even 

 Jess resistance, and he believed that it might now be taken at from -^-c:^^ to 

 J-th, so that consequently a less area of float or propeller, would suffice to 

 overcome the equilibrium and produce less " slip." 



Mr. Smith, of Deanston, observed, that the screw with three blades, 

 vrhich had been used in the Swarf, seemed calculated to produce the best 

 effect. The opening towards the centre of motion, by reducing the arms of 

 the screw blades, as far as the requisite strength would allow, was judicious, 

 as from the comparative slowness of the rotative motion towards the centre, 

 little propulsive effect was produced ; whereas the resistance to onward 

 motion, by the arms, if they had not been reduced, might have been con- 

 siderable ; besides, if the arms were in the part broad, there would have 

 been greater tendency to produce centrifugal action on the water. The 

 gradual alteration of the angle of the blade, to the axis of the screw or 

 onward path of the vessel, was also judicious, as it afforded a greater onward 

 action of the blade at the entrance, whilst it gradually curved round to 

 nearly a right angle with the path, so as to leave the water without causing 

 any revulsion ; it had thus an action in some respects similar to that of the 

 tall of a fish. The salmon, when it " made a run," put down all its side 

 fins, and solely hy the oblique action of the tail, was propelled forward with 

 great force and speed, to which the flexibility and form of the tail, and more 

 especially its curving form to accommodate its leaving the water without 

 causing revulsion, principally contributed. Some years ago, Mr. Smith had 

 made experiments with fans for blowing air, and so far as he could recollect, 

 the form of greatest effect, much resembled in principle, that of the pro- 

 peller under consideration. 



Mr. Farey said, that in order to continue the series given by Mr. Rennie, 

 of steam vessels, which had been recently constructed with screw (or rather 

 oblique-acting) propellers revolving under water, it would be desirable that 

 the meeting should have the particulars of a vessel called the Napoleon, 

 which had been built at Havre by M. Norman, and fitted with engines and 

 machinery constructed in this country by Mr. Barnes. Whilst at Havre last 

 summer, Mr. Farey had very minutely examined that vessel, and he con- 

 sidered it equal to anything that had yet been executed of the kind, and a 

 fair specimen of the perfection to which that mode of propelling, had (up 

 to the present time) been brought for sea-going vessels. Mr. Barnes and 

 M. Norman were well known in their respective departments, and they had 

 heen accustomed to co-operate during some years past. The engines which 

 had been made and sent by Mr. Barnes to France, and fitted in vessels con- 

 structed by M. Norman had, in most cases, paddle-wheels, with moveable or 

 mechanical paddles, on the plan introduced by M. Cave, which possessed a 

 decided advantage over ordinary paddle-wheels: the loss of power occasioned 

 by the paddles entering and leaving the water too obliquely, being much 

 diminished. In comparing the performance of the Napoleon, with vessels 

 fitted with those mechanical paddles, there was less effect produced by the 

 oblique acting submersed propeller, when considered merely as a mode of 

 employing a given amount of power, to propel a given vessel through the 

 ■water in a calm ; but if the same power, as the engines of the Napoleon, 

 had been applied with mechanical paddle wheels at the sides of the vessel, 

 (such as Mr. Barnes had been accustomed to construct,) the vessel would 

 have had more speed in calm weather and smooth water, than had been 

 attained by one revolving propeller, with oblique acting blades, applied under 

 water at the stern ; and it was possible that a greater amount of speed might 

 have been attained, even with well-proportioned common paddle wheels. 

 Nevertheless, the submersed propeller at the stern, admitted of the use of 

 sails, in concert with steam power, or in lieu of it (when the wind was 

 strong, and in a tolerably favourable direction) with much greater advantage 

 than Gould be done in steam vessels, with the ordinary or even mechanical 

 paddle wheels, although the latter were well adapted for acting in concert 

 with sails, because they would perform well, when the paddles were either 

 deeply, or slightly immersed. The proper and most advantageous action of 

 ordinary paddle-wheels was very greatly impaired, by variations of immer- 

 sion ; the mechanical paddles (when properly proportioned) were less influ- 

 enced, and the submersed propeller still less ; in fact, being wholly under 

 water, at all times, its action did not appear to be sensibly atfected by any 

 such alterations of the depth of its immersion, as were likely to take place 

 in the roughest waves, or the greatest variations of draught. When all 

 circumstances were considered, it might be safely concluded, that vessels 

 fitted with revolving submersed propellers, would answer well for making 

 regular sea voyages, either in winter or summer ; and on an average, he 

 thought, that their passage would be performed at least as well (if not better) 

 than those of any steam vessels now in use, and with an economy of fuel, 

 arising from such vessels making a more advantageous use of their sails, and 

 less use of their engine power. 



M. Norman, in reply to questions from Mr. Rennie, regretted that his 

 slight knowledge of the English language, not only precluded him from 

 fully comprehending the narrative of the paper, and the statements of the 

 several speakers, but also rendered it ohligatorv that he should communicate 

 to the meeting in French, the few remarks which he could not withhold, 

 after the pressing notice of the chairman. Many experiments had been 

 made m France, with screw propellers by numerous inventors, as far back as 

 the latter part of the 18th ccnturv, and bv M. Cave aud others at recent 



periods, but the most extensive experiment was that of the NapoUon, for 

 which Mr. Barnes had constructed the steam engines and machinery in 

 England, and which he might be allowed to say had given complete satis- 

 faction. The Napoleon was built at Havre, and launched at the latter end 

 of 1842, for the service of the French Government Post Office in the Medi- 

 terranean. The vessel was built of oak timber, copper fastened and cop- 

 pered. Its dimensions were as under ; — 



Englisti. 



Metres. feet. in. 



Length of vessel from stem to stern . . 47'5 = 155 8 



Ditto at the surface of the water . . 45-2 = 148 6 



Extreme breadth 8-5 = 27 8 



Ditto ditto at the surface of the water . 8"32 = 27 4 



Draught of water when light loaded, abaft . 3-6 = 11 10 



Ditto ditto forward . 2-26 = 7 5 



Sq. metres. Sq. ft. 



Area of the midship section, at the above 



draught of water 13"4 = 144 



Ditto of the surface in contact with the water, 



occasioning friction .... 401 = 4320 



The revolving propeller, was fixed in a space or opening abaft the usual 

 stern-post, (to which, in an ordinary vessel, the rudder would be hung,) and 

 withinside another stern-post, which was erected on a prolongation of the 

 keel, farther aft, for sustaining the rudder, so as to leave a space between the 

 two posts, for the reception of the propeller. The centre of the propeller 

 was (1'82 metre = ) G feet beneath the surface of the water; its diameter 

 was (2-28 metres = ) 7 feet 6 inches, and the highest point of its periphery 

 was 2 feet 3 inches below the water line, when the mean draught of water 

 aft was about 11 '82 feet. Four propellers of the same diameter, but of 

 difl'erent forms, were made, in cast iron, under the direction of Mr. Barnes, 

 and were tried with various success during the past year. The propellers 

 had been altered several times, and it was found that within certain limits, 

 by cutting away the ends so as to shorten the length of the screw, (which 

 had also the eflFect of diminishing the surfaces of the blades,) the speed of 

 the vessel was increased, and the vibration was reduced ; a portion of this 

 effect bad however been attributed to using four arms. A propeller with 

 three blades, occupying the whole of the circle, was first tried ; others which 

 presented less central surface answered better, and the best, which was still 

 in use, had four blades, which occupied -jSjths. of the area of the circle, 

 when viewed in the direction of the axis, leaving -nrths. of that area vacant, 

 for the free escape of the water between the blades, whose obliquity was 

 such as to produce an advance of (3'12 metres = ) 10 feet 3 inches in a 

 revolution. The steam engines were nominally of the power of 65 horses 

 each, = 130 horses together; their cylinders were 45 inches in diameter, 

 their pistons making usually from 27 to 28 double strokes of 3 feet 6 inches 

 in length per minute. The motion was communicated to the propeller by a 

 spur wheel of 126 teeth, working into a pinion of 29 teeth, which gave 

 nearly 4J revolutions for each stroke of the engine, or about 120 revolutions 

 of the propeller per minute. The ordinary speed of the vessel, without any 

 sails being used, was 10 knots or II5 statute miles per hour. She had three 

 masts of considerable height, the rigging being that of a brig forward and 

 that of a schooner at the main and mizen masts, with as great an extent of 

 canvass as would be used in any sailing yacht. When the wind was favour- 

 able and the sails could be used, the speed increased to 11 or 12 knots per 

 hour. After a series of experimental voyages, the vessel had gone to her 

 station in the Mediterranean, where she was now in constant service, and had 

 gone through some rough weather with great success ; her motion was de- 

 scribed as being remakably easy, she rolled very little, steered better than 

 ordinary vessels, for the propeller appeared to give increased effect to the 

 rudder, and the propeller had never been observed to show itself above the 

 water even in the heaviest seas, when the pitching was at its maximum. 

 Plate VII. Figs. 5 and 6, are drawings of the Napoleon Screw Propeller. 



Mr. Galloway remarked, that the properties of a screw with an increasing 

 pitch, had been slightly investigated by Tredgold, in his work on the Steam 

 Engine, p. 310, so early as 1827. The author had briefly referred to the 

 subject of screw propellers, and had given some logarithmic calculations of 

 their properties, from which he drew the conclusion, that the true screw 

 could not be carried beyond a single convolution, with any good effect ; 

 whereas by a progressive increase of the pitch, the propelling efl'ort would 

 be continued, until the spiral became expanded into a straight blade parallel 

 to the axis. It was Mr. Galloway's opinion, that more was to be expected 

 from ascertaining the best position for placing the screw, with reference to 

 convenience and effect, than from any slight change in the form or the 

 number of the blades of propellers. 



Mr. Samuda said it appeared to him, that the action of the propeller 

 tended to drive the water from it at a right angle with its surface, and as it 

 formed a diagonal line with the keel of the vessel, some portion of the force 

 was not efliciently used for propulsion ; he conceived therefore that by a 

 judicious arrangement of shrouding, round the extreme circumference of the 

 propeller, the diagonal currents of the water, might be diverted into a di- 

 rection parallel with the way of the vessel, and thus cause the whole of the 

 reaction to become available for propelling. Such an arrangement would 

 enable propellers of a much coarser pitch to be employed, and their speed 

 being reduced in proportion, they could be more readily driven directly by 

 the engine, without the intervention of bands or gearing. 



