1840.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



387 



feeling in favom- of a high proportion of power to tonnage. It has been found 

 by some of tlie best mercantile companies that a high proportion of ])ower to 

 tonnage is not only better for expedition, but also more ecouomical of fuel 

 and of capital ; and instances are frequent of an increase in the power of a 

 steam vessel, producing a diminution in the consum])tion of fuel. As this 

 question is becoming every day of greater importance, it is proper to examine 

 it carefully. In the first place, it is known that the proportion of power must 

 be very much increased to gain a given increase of speed ; — thus, if ten horses 

 power propel a vessel through water five mile an hours, it will require forty 

 horses power to propel the same vessel ten miles an hour ; since it will re- 

 quire a quadruple power to obtain a double speed, in like manner it will re- 

 quire a ninefold power to triple the speed. A large power of engine, it may 

 be said, occupies nuicb useful space which might be filled with cargo. It 

 consumes much coal, and the speed is by no means proportioned to the ex- 

 pense of fuel and machinery. But this is a limited view of the subject. If 

 time, as an element, and a very important one in the value of mercantile con- 

 veyance, be calculated, then it will be found that in many cases the effects of 

 high speed, at any expense of fuel, will compensate for that expense. But it 

 is not on the value of speed at the present day that we proceed in this in- 

 qiiiiy. We are to ascertain what may be the best proportion of power to 

 tonnage in sea-going vessels. We have seen that the lowest speed is the 

 most economical, and that it requires expensive additions to give high veloci- 

 ties. But in arriving at this conclusion, we have taken only the case of smooth 

 water : here it is obvious that the smallest power will be most economical. 

 But it should be remembered that the great purposes of steam arc generally 

 of a different natOTe from the mere generation of motion through a quiescent 

 fluid. The force of adverse winds, waves, and tides are to be overcome, — and 

 it is the success of steam in olitaining regularity and speed, in spite of these, 

 which constitutes its superiority. Now. if we take a simple case of one of 

 these, we shall soon find that a higher proportion of power to tonnage may 

 be essential not only to speed hut even to economy. Suppose, a steam-boat 

 with a small proportion of power, capable of propelling the vessel at the velo- 

 city of three miles an hour through still water, to be applied to stem a cur- 

 rent of three miles an hour, or a proportionately strong breeze,- — is it not 

 plain that the vessel would make no headway .' This extreme case of too 

 little power shows that there is at least one proportion of power which is too 

 small for economy of fuel. We may now proceed to investigate the question 

 of best proportion, or the point where the attainment of high speed is accom- 

 panied by absolute saving of fuel, as compared to lower velocity. For this 

 purpose we merely take it for granted, that the speed through the water will 

 be nearly as the square root of the former, according to the general law of 

 the resistance of fluids ; that the resistance offered by adverse winds, &c. has 

 been ascertained, and is determined on a particular station, that is, that it is 

 known that on a given station, a given vessel, with a given power, makes a 

 voyage in adverse circumstances in, suppose, double the time of her most 

 prosperous voyage, say her prosperous voyage in fourteen, and her adverse 

 voyage in twenty-foiu- days, being a retarding power of ten days out of twenty- 

 four ; we take this retardation of ten days as the measure of the retarding 

 power of adverse weather in the given circumstances. By working out the 

 result, we obtain the very simple rule for finding the best proportion of power 

 to tonnage : from the square of the velocity of any given vessel in good 

 weather, subtract the square of the velocity of the same vessel in the worst 

 weather, divide the difference by the square of the velocity in good weather, 

 and the quotient multiplied into double the horses' power of the said vessel, 

 will give the power which would propel the same vessel in the same circum- 

 stances, with the smallest quantity of fuel. It further appears, that the con- 

 sumption of fuel in the worst voyage, will not exceed that of the best voyage, 

 in a greater proportion than 10 to 7— that is to say, for 70 tons of fuel burnt 

 on a good voyage, it will not be necessary to carry more than 100 tons, in 

 order to provide against the worst. Let us take, as example, a Transatlantic 

 steam-ship, which has a proportion of 1 horse power to 4 tons of capacity ; 

 her unfavourable voyage being, between England and America, twenty-two 

 days, and her favourable voyage fourteen davs, being a comparative velocity 

 7 and 11. 



„2_»'2 121—49 72 12 



Then A' = 2 V 



»'2 121 

 — =2 



49 „ 72 __ 



= 2 = r- nearly. 



121 121 10 ' 



Hence the power should be increased in the ratio of 6 to 5 — that is to say, 

 the engines at present capable of exerting a power of 500 horses should have 

 been capable of exerting a power of 600 horses, and would, in this case, con- 

 sume less fuel, as well as produce greater regularity. The following result 

 also follows : — The vessel of less power burns 30 tons per day, performs the 

 distance in fourteen days, consuming 420 tons of coal in fair weather. The 

 vessel of less power burns 30 tons, performs the distance in twenty-two days, 

 consuming 660 tons in foul weather. The vessel of greater power burns 36 

 tons, performs the distance in twelve and a half days, consuming 468 tons in 

 fair weather. The vessel of greater power burns 36 tons, performs the dis- 

 tance in 17'5 days, consuming 630 tons in foul weather ; being a consumption 

 of 64 tons less fuel, and performing the journey in four and a half days less 

 than the other. It is manifest, that the store of fuel carried in the vessel 

 with less power, must, on all occasions, be equal to the greatest consumption, 

 that is to say, at least 660 tons, whereas 630 tons will be sufficient for the 

 vessel of greater power, and, as in all vessels for long voyages, coals carried 

 are much more costly than the mere price of coals, or as the freight of the 

 vessel is more costly than the fuel, coals carried are to be reckoned at least 



as expensive as coals burnt. Moreover, as the gain in time is 4 J out of 22, 

 !)eiug 20 per cent., it is plain that the vessel may lie calculated to do the dis- 

 tance oftener in a year, because, as the times of starting must be regulated 

 not by the shorter, but by the longest period of a voyage, seventeen and a, 

 half days in the one case, stand in the place of twenty-two in the other. It 

 appears, therefore, that, for long voyages especially, there are great advantages 

 in point of economy, certainty, and speed to he obtained by the use of vessels 

 of a higher power than usual ; and that in a given case, the best proportion 

 of power to tonnage may readily be determined from the rules already laid 

 down. In regard to absolute or definite proportion, it may be stated, as the 

 result of the best vessels, that the proportion of power to tonnage should not 

 be greater than one horse power to two tons, nor less than one horse to three 

 tons ; the greater proportion holding in the smaller, and the less proportion 

 of power in the greater vessel. 



Mr. Fairbaim agreed, that the horse power should be increased, but that 

 in bad weather the consumption of fuel was not so great as in fine weather.— 

 Mr. Russell said, that practically in good weather the engines are worked ex- 

 pansively. There are two systems. The south engineers are afraid of using 

 full powers ; they use smaller proportions of power to tonnage, and slack the 

 power in head winds. The north engineers always set head to wind in bad 

 weather, and work full power ; and in good weather work expansively. lu 

 steamers worked on the south system, the advantages would be as Mr. Fair- 

 baim stated ; in steamers worked on the north system, the advantages would 

 be as he stated. — Mr. Fairbairn was of opinion, that three tons to one horse 

 power were better than four to one. — Mr. Russell said, that it was safe to 

 give more power than the ride gives ; that on the introduction of longer and 

 sharper vessels less power would be required. — Mr. Fairbau-n observed, that 

 the goverment post-office steamers, in the Mediterranean, were so bad, that 

 the French vessels constantly pass them. 



Mr. Smith made some observations " On the Drainage of Railway Embank- 

 menis and Slopes." — Mr. Vignoles observed, that had Mr. Smith had as much 

 experience on railways and their constructiou as himself, he would have 

 known that all he had recommended had been done on various occasions, 

 whenever the expense could be justified. 



Mr. Mallet •' On the Action of Air and Water on Iron." — Mr. Mallet 

 stated, generally, the nature of the principal practical results obtained by him, 

 with respect to the durability and modes of protecting cast iron, wrought 

 iron, or steel, under various conditions, when exposed to the corroding or 

 chemical action of air and water, whether fresh or salt. These researches 

 have been made under the sanction of the Association, and are still in pro- 

 gress. Numerical results have ah-eady been obtained of the absolute and re- 

 lative durabiUties of about 100 different varieties or makes of cast iron and of 

 wrought iron, in each of the following conditions as to water, — viz. In clear 

 sea or ocean water ; in foul sea water, as in the harbours of large cities ; in 

 clear river water ; in foul river water ; in sea water at high temperatures ; in 

 sea water at various depths ; in sea water of variable saltness. The residts 

 in all these cases are given in voluminous tables, so arranged as to enable the 

 engineer to predict with confidence the durability of a given scanthng of iron 

 of a given sort, under given cuxumstances. The conditions of corrosion of 

 iron, in contact with copper, with zinc, and with tin, and with various atomic 

 alloys of these, have been determined, and printed tables of the results dis- 

 tributed to the Section. Results are also given as to the relative protecting 

 power of several paints or varnishes, to the surface of iron exposed as above. 

 The specific gravities of all the irons experimented on, have been taken by a 

 new method, and the increment of specific gravity due to increased depth (or 

 head of metal) in castings determined, and also the decrement of specific 

 gravity due to increased bulk or scanthng of castings determined. These are 

 necessaiy data to the foregoing investigation, and are in themselves of im- 

 portance to the engineer, with reference to the ultimate cohesion of cast iron, 

 which seems to be related, and probably is some function of the specific gra- 

 vity in any given case. The experiments are now extended to wrought iron 

 and steel ; a final report is proposed, to consider the nature of the chemical 

 changes induced on cast and wrought iron by the action of sea water, and to 

 complete the numerical results now given, which have lately been in several 

 instances submitted to control, or tested by the actual corrosion of castings 

 recovered from the wrecks of the Edgar and Royal George, &c., and found 

 strikingly to coincide. 



Mr. Grimes described Dennett's Rockets for preserving lives from ship- 

 wreck, and read a letter from Capt. Denham, stating that the range of these 

 rockets exceeded that of the mortar by 100 yards, the range of the rockets 

 being about 350 yards, while that of the mortar was but about 250. 



Dr. Wallace on Arches. The object of this paper was to exhibit a method 

 for geometrically constructing a catenary. After explaining Ids method. Dr. 

 Wallace stated that he was about to pubhsh a set of tables for constructing 

 the catenary, and also for suspension bridges. 



Mr. Wallace exhibited and explained his smoke protector. — Mr. Haw- 

 kins exhibited and gave an account of Mr. J. R. Bakewell's instrument for 

 measuring the angles of the dip of strata. — Mr. Rayner exhibited a machine 

 for regulating the speed of macbinerj' in cotton-miUs, &c. — Mr. Smith, of 

 Deanston, exhibited a model of a new canal lock, the advantages of which 

 he stated to be, that the descent in each lock would not be more than twelve 

 to eighteen inches — that the locks were opened by the passage of the vessels 

 — that the locks shut of themselves— that the vessels did not require to stop 

 —and that Uttle or no water was lost. The lock gate is hinged at the hot- 



