1841.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



203 



PROCEEDINGS OF SCIENTIFIC SOCIETIES. 



INSTITUTION OF CIVIL ENGINEERS. 



February 9. — The President in the Chair. 



Mr. S. Seaward explained the Table of Velocities of steam ships, which 

 accompanied his paper. (See Journal for last month, page 168.) 



Tlie top line of tigures represents the number of horses power, ranging 

 from thirty to three hundred. The side line gives the tonnage of the steam 

 ships, rising progressively from one hundred to twelve hundred tons. The 

 intermediate si)aces show the number of knots or nautical miles, which a ship 

 of given tonnage, with a certain power, will travel through still water per 

 hour. 



The tonnage is calculated by the old rule (13 George III. cap. 74) : " From 

 the lengtli substract fths of the breadth, multiply that sum by the extreme 

 breadth in the widest part, and again by i the l)readth, divide the product 

 by 94, and the quotient will be the true tonnage." 



The Table is constructed upon the principle, that each vessel of a good 

 modern form will carry, at a proper draught, a weight equal to her measure- 

 ment tonnage, and is presumed to be loaded equal to her tonnage, either by 

 the weight of her engines, fuel or cargo, and it tenuinates at thirteen knots, 

 at which speed the engines alone become the full load of the ship. The 

 mode of constructing and of using the table was fully described, and e.xam-' 

 pies were given. 



It was shown, that an engine of thirty horses power would propel a ship 

 of twelve hundred tons burtlien, at the rate of 4 knots per hour, while three 

 hundred horses power would only propel the same ship at the rate of 10| 

 knots i)er hour. Hence, ten times the power would only produce about two 

 and a lialf times the speed. 



The principal points in the paper were more fully dwelt upon, and in an- 

 swer to questions from some of the members, Mr. Seaward remarked, that no 

 steamer in England had ever been propelled at more than fifteen geographi- 

 cal miles per hour, through still water. 



lu some of the Government mail packets, the engines and coals were the 

 full cargo of the vessel. The table did not apply to vessels overladen with 

 power, for as the weight increased in the ratio of the power, so the immersed 

 sectional area was augmented, and the lines of the vessel which might be 

 well calculated for speed when at a proper draught, became lines of retarda- 

 tion, and the engines did not work up to their proper speed, owing to the 

 deptli to which the paddle floats were immersed. For instance : — Tlie wheels 

 of the "British Queen" have been plunged between six and seven feet, in- 

 stead of four feet, which was the calculated dip; the engines at the same 

 time diminishing their speed so much as to reduce the efl'ective power from 

 five hundi-ed horses to nearly three hundred horses. 



The only advantageous way in which great power could be applied, would 

 be by contriving to prevent the increase in the weight of tlie machinery and 

 fuel, and those engineers, would be most successful who could so apply the 

 materials of constraction, as to ensure strength without the usual correspond- 

 ing increase of weight. 



Mr. George Mills, from his experience as a ship-builder, at Glasgow", was 

 enabled to confirm all that Mr. Seaward had advanced. On the Clyde, the 

 employment of an excess of power in steam vessels bad been carried to the 

 greatest extent, without producing corresponding advantages, either for speed, 

 or in a commercial point of view. It would appear that the same error had 

 to a certain degree been committed on the Thames, l)ut less than on the 

 Clyde ; for on the latter river there were vessels with nearly double the 

 power, in proportion to size, as compared with any vessel on the former river. 

 He believed that on the Thames no vessels bad so much as one horse power 

 for each register ton, whereas on the Clyde, there were steamers of seventy 

 to eighty tons register, having single engines, with cylinders of fifty-four 

 inches diameter, which was more than one hundred horses ))ower. It would 

 appear that this application of extra power had only obtained a very moderate 

 speed, while the great first outlay, with the commensurate cm'rent expenses, 

 had reduced the conmiercial profit to the lowest point, — of this the proprie- 

 tors alone could give any account ; but as to the speed attained, he had seen 

 three steamers of identical tonnage leave the Broomielaw at the same time, 

 their engines being respectively of one hundred and ten, eighty, and sixty 

 horses power ; yet their speed was in the inverse ratio of their power ; the 

 vessel with the smallest engine arrived at Greenock first, the greater power 

 second, and the greatest last. Tliese remarks were only applicable to river 

 boats. \\'ith regard to sea-going vessels, the system had not been carried to 

 so serious an extent, yet with them tlie average proportion was about one 

 horse power to two register tons, and some few reached as high as one horse 

 to one and one-eighth of a ton. 



As an example of an augmentation of power producing an opposite result 

 from that which was intended, Mr. Mills mentioned two vessels called the 

 " Torfar" and the " Rover," built by him and his (then) partner, Jlr. Charles 

 Wood. They were each of about two hundred and twenty tons register, 

 built from the same draught, and in every respect as similar as possible — ex- 

 cept that the engines, which were by the same maker, were respectively of 

 one hundred and seventy, and one hundred and thirty horses power ; yet 

 whene\ er they worked together, the one with the smaller power proved her- 

 self the faster vessel, either in a calm, with the wind, or even against it. The 



" Achilles," Liverpool steamer, which lately had an addition of thirty feet to 

 her length, and eighteen inches to her breadth, augmenting the tonnage about 

 one-fifth, had improved her speed upwards of one mile per hour, although 

 she carried a much heavier cargo than before. 



He had built a vessel of five hundred and sixty tons register, vrith engines 

 of one hundred and thirty horses power on board — a proportion of power to 

 tonnage of one to four ; the stowage for cargo was ample ; the accommoda- 

 tions for passengers excellent. She drew little water, and her speed was 

 much greater than vessels of double her power. Yet in spite of all this, the 

 vessel could not find a purchaser, because the power was not nominally large. 



It would be asked — why, witli these and so many similar instances,'such a 

 system was continued 1 It was not likely that the engineers would complain 

 of having orders for large engines ; and there were certain dimensions pre- 

 scribed for the vessel, to which the ship-builder was under the necessity of 

 conforming. 



The chief cause of mischief, however, was the fiat of the pubUc. It was 

 believed that a great power would remedy want of speed and all other evils, 

 and it was found indispensable for ensuring the confidence of travellers. 

 Hence, the shipowners, who depend upon the pubUe for support, were ob- 

 liged, against the conviction of their experience, to keep up the errors occa- 

 sioned by ignorance. 



The President observed, that the condemnation of large power should not 

 be carried too far. as experience alone had produced the increase of weight, 

 strength, and power, of the present engines, compared with those of the early 

 steamers which were built, instancing ihe Halifaj: Packets (Cunard's), which, 

 with their great power in proportion to tonnage, had performed their duties 

 satisfactorily. 



Mr. Mills explained that the Halifax Packets were built for the especial 

 purpose of carrying the mails only, to perform the voyage in a given time, — 

 about twelve days. The engines were built by Mr. Robert Napier, after the 

 model of those of the •' Great Western," which used their steam expansively ; 

 similar provisions had been made in the Halifax Packets, but the expansion 

 valves were seldom used. 



Mr. Field agreed with the princijial part of Mr. Seaward's paper, but he 

 would prevent an erroneous conception of the term overpowering a steamer. 

 A vessel could not have too much power, provided that power could be ad- 

 vantageously applied, without causing too deep an immersion. A good result 

 could be produced only by keeping a proper proportion between the machinery, 

 the vessel, and the paddle wheels, and immersing the hull of the steamer only 

 as deep as the true lines of draught. 



Mr. Vignoles observed, that in this country the reputation of engineers de- 

 pended upon the commercial success of the works they engaged in. An er- 

 roneous public opinion might have influence at present ; but if the engineer 

 and ship-builder would determine to break these trammels, and produce such 

 vessels as should force conviction upon the public mind by the speed attained, 

 and show the proprietors the consequent commercial advantage, the present 

 system would soon be abandoned. 



Mr. Parkes eulogized Mr. Seaward's candour in describing the errors in the 

 first construction of the engine on board the Vernon ; more was frequently 

 to be learned from failures than from successful efforts, and no communica- 

 tions to the Institution would be so useful as those which gave accounts of 

 defective design or construction, with the details of the methods adopted for 

 remedying the defects. He directed attention to the performances of the 

 " Great Western " steam ship, wliich at least equalled those of the Halifax 

 Packets, without the disadvantages of being unable to cany cargo, or of ship- 

 ping so much sea, when the weather was foul. The important featuie of 

 economy of fuel on board the " Great Western" might be in part attributed 

 to the use of steam expansively. It was very desirable that the Institution 

 shoiUd possess very full drawings and a description of the " Great Western," 

 so as to be enabled to compare them with those of the Halifax Packets, 

 which had been promised Ijy Mr. George Mills. He would impress upon 

 manufacturers of marine engines tlie necessity of adopting a correct and uni- 

 form nomenclature of the power placed on board steam vessels. The nomi- 

 nal sailing power did not accord with any calculation. 



Mr. Field believed the Table of A'elocities calculated by Mr. Seaward to be 

 very nearly accurate. The speed of the " Great Western," when loaded to 

 her proper draught, has been as high as 13^th miles through still water. 

 There was an error in the alleged speed of Cunard's vessels ; they reached 

 HaUfax in ten days, Boston in three days more, and then had still one day's 

 voyage to New York. The average duration of the voyages of the " Great 

 Western," was about fourteen days and a half. If two hundred tons were 

 deducted from the tonnage of the " Great Western" for cargo and the ac- 

 commodation for the passengers, she would then be similar to the Hahfax 

 Packets. The engines of the •' Great Western" were nominally estimated at 

 four huncked horses power, and the average consumption of fuel was twenty- 

 six tons every twenty-four hours. 



During the discussion, Mr. Cubitt had calculated the following Table, 

 showing the rates of velocity which would be attained by substituting engine 

 power, with its consequent weight of one ton per liorse power, for cargo, so 

 as to preserve the draught of water the same in all cases. 



Mr. Seaward remarked, that his Table of power and velocities was corro- 

 borated bv Mr. Cubitt's— the practical results verified both. The great dif- 

 ference between the " Great Western" and the Halifax Packets consisted in 

 the better adaptation of weight and power to tonnage, and the more econo- 

 mical consumption of fuel of the former over the latter— the one carrying 



