1 845.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



323 



Decks. — The upper cargo deck forward is made of platp iron, -^ incli thick 

 in the middle, tnil ,"j inch roimd the sides ; it i3 riveted together ihrough- 

 oul, as well as to the iron deck heams, and to the sides of the vessel. The 

 main deck is made of [line lindier 5 inches thick, and the planks are cross 

 bolted at distances of 4 feet a-part. As this deck is situated on the load 

 floatation plane of the vessel, where transverse stiffness is of more importance 

 then longitudinal strength, the planks are placed athwarlships, and their ex- 

 tremities are firndy holted <l()wn, tlirough two longitudinal stringers of 

 Ualtic tind)er, to the shelf plates, which are 3 feet wide hy 5 in thick, and 

 arc very securely fixed to the sides. The middle or promenaile deck is also 

 of pine timher 4 inches thick, placed lengthwise of the ship; it has also 

 strong iron shelf plates 3 feet wide hy J inch thick, and lialtie stringers to 

 attach it to the sides of the sliip. The upper deck is of red pine timher, and 

 is also placed lengthwise. As the sides of the vessel at this height, and also 

 this deck, may he considered as the truss, which is to resist longitudinal de- 

 fliction, or drooping of the extremities, the outside plates are there J inch 

 thick, and they have heen strengthened hy an outside nioulding-iron strap, 

 C inches hy 1 inch, and hy additional straps of iron 7 inches hy 1 inch, 

 welded into lengths of (JO feet, and riveted to the inner sides of the up|)er 

 line of plates. The shelf plate of the deck is 3 feet wide hy J inch thick, 

 and upon this, outside of the water-way plank, which is 4 J inches thick, 

 there is a course or tic of Baltic pine timber 340 inches in section, carefully 

 scarphed and sei urely bolted to the ribs, and to the shelf plate, throughout 

 the length of the ship. There are three rows of timher pillars, or staun- 

 cheons, which are fixed to the bottom of the shi|), passing up between longi- 

 tudinal tics at each deck, ami are secured to the upper one. The beams 

 of ail these decks are made of single iron, G inches hy 3* inches by ! inch, 

 and their ends are bent down, an(l riveted to the rihs on each tide. I'pon 

 them, the shelf plates before roentioired are riveted, and ibiisform a horizontal 

 hand 3 feet wide at each deck. A crutch or strut is intrciduccd at each end 

 of nearly every deck beam, which is riveted to it, and to the ribs at about 

 3 feet from the angle of junction. 



Division by bulk heads. — One of the most important improvements which 

 has recently been introduced in the construction of vessels (particularly those 

 of iron), is the water-tight bulkhead ; as in the greater number of cases, 

 when an injury may he sustained in one compartment only, it may absolutely 

 preserve the vessel from sinking ; several iirstances of this have already 

 occurred, and even where it may not sulfice for this purpose, it at least 

 separates the leaky and injured from the secure parts, and gives time either 

 to attempt to stop the leak, or to make other preparations. In iron vessels, 

 these bulkheads can lie made much more effectual than in wooden ones, hy 

 their exact contact with the bottom and sides, while at the same time they 

 form admirable ties and st.ffeners. In the Great Britain there are five sucii 

 bulkheails. The first separates the forecastle from theforward passengers' cabin 

 and hold, and as it is in the forepart of a vessel that injury is most likely to 

 be sustained, this partition is made particularly strong and secure. The next 

 bulkhead divides the forward cabin from the engine-room, or more properly, 

 from tlie fore-hold for the coal and the stokers, at the forward end of the 

 boilers. The third bulkhead is abaft the engine-room, but in this tliere is 

 necessarily a hole for the screw shaft to pass through; this is secured hy a 

 well fitted collar, and there is also a door, which is so arranged as to be sl.ut 

 and bolted quickly. These three bulkheads pass up to the upper deck ; there 

 are also two others ; one separating the after coal-hold from the after cargo- 

 hold, and another nearly at the stern ; both these terminate under the saloon 

 deck. 



Screw Propeller. — At an early stage in the construction of the Great Bri- 

 tain, but not until her sides had assumed the form adapted for paddle wheels, 

 the snrall steamer Archimedes, belonging to the comparry owning the patent 

 of Mr. F. P. Smith for the application of the Archimedean screw, visited 

 Bristol, aird amongst other parties irrvited to make an excursion to the 

 Holmes, on board of her, were some of the directors of the Great VAestern 

 Steam Ship Company. The performance of the screw on that occasion in- 

 duced the author to requested permission of Mr. Smith and Cuptairr E. 

 Cbappcll, R.N., who were officially appointed by the Admiralty to report 

 upon her, to proceed in her to Liverpool. On the passage, enorrgh rorrgh 

 weather was encountered to show that the screw possessed several good 

 poirrts, and was not so absolutely impracticable as had heen asserted ; and 

 although far from venturing to give a decided opinion, on the author's re- 

 turn, be wrote such a letter to the Board of Directors, as induced them, alter 

 some days of deliberation, to deride upon suspending, during three months, 

 the progress of the machinery for paddles, and also that part of the vessel 

 which might be affected by the change, and to call upon Mr. Brunei during 

 that period to investigate the subject. At the errd of the proposed delay, 

 the report which Mr. Brunei nrade was so favourable, that, undaunted by 

 the novelty and vastness of the experiment, the directors resolved to adopt 

 this mode of propulsion, of the success of which they have now such cause 

 of congratulation. From that iieriod, until it became necessary to decide on 

 the exact form of screw to be used, all possible nreans were taken, by experi- 

 ment and observation, to arrive at the best shape and angle of inclination of 

 the blades, or as it is commonly called " the pitch." Amongst others, the 

 proprietors of Mr. Smith's patcrrt lilrerally lent the Archimedes to the Great 

 Western Steam Ship Company, for a period of several months, which afforded 

 ample opportunity of tryiirg the performances of the several forms of screws 

 recorded ia the following table ; — 



Performances of the several forms of Screws. 



537 

 63-89 

 67-13 



62-6 

 62 12 



r &' 



Smith's two half threads, mndc 

 of wrought Irun. 



Ditto dUto 



Ditto, mode of cast iron .... 

 Ditt ditto 



Woo(lcroft*8 incrensinff pitch, 3 1 



blutiea, made of cast iron, B0 



tirst made. 

 The anmr. with 3 inches cut off 



the termination uttlie blades. 

 The same, with 4 inchea cut eff 



the entering edges of thel 



blades. 



4 wrought iron arras, with blades,! 

 etieli 2 feet 9 inches long, byj 

 1 foot broad. 



These experiments were made in the British Channel under circumstances 

 of weather, as nearly as possible similiar, arrd the distances were very care- 

 fully measured by two of Massey's Logs, whose accuracy had been previously 

 tesled. It will be observed, that the greatest velocity of vessel, 8. .37.') knots, 

 was attained by Mr. Smith's screw of 5 feet 9 inches diameter, the angle of 

 which was 19} degrees, and the slip was 21 per cent.; that is, the ratio of 

 speed of the vessel to that of the sci-ew, was as -787 to 1. Particular atten- 

 tion is due to experiments Nos. 5, G, and 7. Reasoning upon the assump- 

 tion, that the eftbrt of the enterirrg edge of each blade, must cause the water 

 to recede, and that each succeeding portion of blade should so increase in 

 pitch, as to impinge with uniform force against the water, which was so re- 

 ceding, a screw of this description was nrade and tried before it was dis. 

 covered that it was the subject of a patent hy Mr. Woodcroft. The first 

 tri-ii served to show, that the curvature or increase of pitch, which had been 

 given to it, was too great, since the speed of the vessel was greater by 2 per 

 cent, than that due to the mean pitch of the screw, whence it was evident, 

 that the entering edge was really retarding, and the ternrlrraling portion 

 alone was doing the duty. On the second trial, when a radial strip, 3 inches 

 in width had been cut off the after part of each blade, the speed of the vessel 

 was exactly that due to the screw ; whence it was also evident, that the front 

 edge still did not assist. On the third trial, after a second radial slip of 4 

 inches had been cut off the entering eilge of each blade, the vessel attained a 

 speed of 82 knots, and the ratio of speed of the vessel was as '94 to 1 of the 

 screw. 



The horse power employed on this trial, was by indicator, 6212, and the 

 speed of the vessel 82 knots, against G7'l in the before-namrd trial, with 

 the original screw of the Archimedes, when the speed she attained was 8-37.5 

 knots. Although, on neither of the trials nuiubered 5. G, arrd 7 with this 

 screw, was so great a speed of vessel attained, as on that first named, it is 

 important to draw attention to the fact, that the slip was reduced to a very 

 srtiall quantity. But the horse power exerted was also much less than 

 in the first trial, arising from some imperfections in the cutting down of the 

 screw, and other causes which would probably have been remedied had there 

 been time to cast a new screw of this description ; but unfortunately, just at 

 this period, the Propeller Company required the Archimedes for service, and 

 the experiments ceased. This screw was afterwards tried by Mr. Barnes, 

 in the Napoleon, a very beautiful French Post-Office vessel, brrilt by .M. 

 Nonnaird, of Havre, when the foUowirrg result was obtaiired: — Horse power 

 exerted, 95-5; speed of vessel in knots, 10 15; speed of screw, 11-2; speed 

 of vessel to T of screw, -895 = 10^ per cent. In the two cuttings down, 

 this cast iron screw with three blades, 9 feet in diameter, which was originally 

 very slight, had been so much reiluccd in substance, that it weighed only 

 833 lbs. Mr. Barnes, therefore, could not venture to permit the engines to 

 exert their full power, otherwise it is probable that a higher speed would 

 have heen attained. The commencing angle of 17°, and the terminating one 

 194"; the increase of pitch is therefore ,'ith, or 8| per cent. The screw of 

 the Great Britain, which is of wrought iroir, consists of six arms, formed hy 

 placirrg and riveting together four distinct forgings, or centre pieces, with 

 arms welded to them, each of which is G inches thick. Upon the extremi- 

 ties of these are rivetted palms of plate iron, which are 4 feet 4 5 inches long 

 on their circumferential edge, hy 2 feet 9 inches in height, and I inch thick. 

 The diameter is 15 feet 6 irrches, and the pitch or helix of one revolution is 

 20 feet, which equals an arrgle of 28 degrees. Its weight is 77 cwt. The 

 area of the six palms, which may be corrsidered as the effective part of the 

 screw, is 5625 feet ; but the area, calculated as a plane perpendicular to the 

 exis, that is, as portions of a disc, is only 4 74 feet, and the portions of the 

 arms within the blades, present a sinrilar area of 20.88 feet. As the rotary 

 velocity of the outer edge of the blailes is nearly 30 nrilcs an hour, it is im- 

 portant, in order to dimiirish friction, that they should by as accurately 

 shaped as possible, and should present no irregularities of surface. In this 

 instance, the object was attained, hy mounting t're screw on a face plate and 

 planing the surface, hy means of a tool, to which the proper motion was 

 given ; after which, it was painted several times, rubbed very smooth, and 



