Discussion. the Somerset Dock at Malta

368 TRE SOMERSETDOCK MALTA. AT Mr. REDMANremarked that, almost coincidently with the com- mencement of this work, a Paper was read by Mr. Edwin Clark,’ describing the mode adopted by him for raising vessels out of the water, under exceptional conditions ; and only last session a Paper had been read by an American Engineer,2upon the dock at Pola, under conditions similarly antagonistic to a graving dock. After due inquiry the authorities appeared to have reverted to the stereotyped form of graving dock in England, which was so admirably adapted for the Mersey with a variation of 30 feet, and for the Thames of 20 feet of tide. But on the tideless shores of the Mediterranean, it might have been supposed that all theconditions were in favonr of the modern adaptation ; more especially as this work, however well-executed and superior in character, hadinvolved the expenditure of a very large sum of money. It was stated that the dock and entrance hadcost .S150,000, that it had taken six years in construction, and certainly this longperiod, and thefact that the dock itself was onlycapable of receiving one vessel at a time, were elements in theconsideration of the great cost of this work. He had on former occasions given the cost of docks in various places. On the Thames the dock value, taking the sectional accommodation or contents of the dock below the flotation level, varied from <o fl 10s. per cube yard ; and in the case of the Trafalgar dock at Woolwich Dockyard, which was a most extravagant work in every respect, where there was an addition of .!iu per cent. in the depthof foundation, the cost of the dock amounted to X4 per cubic yard of internal accommodation ; and theBoston dock in theUnited States cost rather more. The Somerset dock, excavated in rock, and faced with ashlar, cost from 23 to S4 per cubic yard of sectional accommodation, inclusive of the cost of the entrance necessary for the approach to the dock, but not adding to its docking capacities. If the cost of the entrance were deducted the cost would be nearly one-half. (See note in next page.) The outline wason the type of the old Liverpool dock--straight sides as contrasted with a section less highly inclined and more parallel to theships’ sides. The most important advantage of that was that it reduced the first cost, inasmuch as the amount of ex- cavationand the expense of pumping were less; secondly, the amount of pumping each time a vessel was docked was reduced, and the trouble andcost of docking was lessened, as short.er shores were sufficient for sustaining a vessel ; but it had this disadvantage,

Vide Minutes of Proceedings Inet. C.E, vol. xxi., page 292, Vi& Ibid., vol. xxxii., p. 65.

that the space between the inside of the dock and the skin of the vessel was so small, that the lightfor working at thebottom of the ship was reduced. This dock, in many respects, was similar to theLiverpool docks and to some on the Thames. In all its features it presented the same characteristics. The docks on the shores of the TJnited Kingdom were drained intoa river or tidalsea ; and the earlydock- builders of Liverpool and London tilted thedock head upwards from the river into which the dock drained. In this case, however, with a constant head of water outside, there would be no advantage in that respect, because the water must be pumped out every time a vessel was docked. The dock at Malta might have been drained either towards the head or stern, or from the centre towards the head or stern, enabling a reduction to be made in the amount of excavation in the bottom. No doubt the work itself was a first- class one ; and it would leave asindelible footprints of Saxon dominion in Malta as had been left bp that remarkablebrotherhood the ancient military and semi-monastic order of the Knights of St. John. Mr. HEMANS,Vice-I'resident, observed that the method of exca- vatingbeneath the cofferdams into the open sea andleaving a roof to be afterwards blown up by electric apparatus, in sections, was novel and deserved high credit. The ordinary caisson was an oblong \-esse1 which was grounded against a sill, and kept tight by timber sides ; but this seemed to be a trough running upon rails, and he did not understandhow the caisson was kept tight.

NoTs.-The followingbtatement of the cost of graving docks might prove interesting. The greater depth and di%cnlty of the foundations of some as compared with others would materially affect the comparison. , l Cost per Cubic Yard. SX- Depth on the i Sill in Feet. Site. Makrial. 1 tional Capxity, bdow l Flotatiur~Level.

16 to 20 Thames. . . . Timber nnd Brick 1oS.to EL NavalArsenals . S1 18s. toE2 10s. 27 Thames Dock Co. . Brick and Sldne . $1 18s. 6d. Sunderland. . . Rock-faced . . $1 76. 8d. to S1 96. 25 Southampton . . Brick . . . . E2 to E3 26 Woolwich . . . Stone . . . . E4 to E4 168. 5d. Somes, Blackwall . Brick . . , . fl Is. Od. Boston, U.H. . . .. X4 11s. Od. 27 Birkenhead . . El 176. Od. Malta, Old Dock . .l €3 146. Od. 33 5 Do.,Somerset . . E3 6s. 8d. Do., without Entranc:c. '2 ' os. Od. .

118'71-72. N.s.~ 2B Downloaded by [] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. 370 THE SOMERSET DOCX AT MALTA. Mr. BEARDMOREsaid he apprehended the caisson rolled out on rails, and then took a flat bearing against the Gill. He supposed that its action was quite independent of flotation, which was a great advantage. The excavation of the rock under the Sea outside the cofferdam was one of the most remarkable feats that had ever been described before the Institution.. Nr. J. G. C. C. GODSWANsaid, having visited Malta two or three times, he considered that the class of dock and site selected were possibly those best adapted to all the circumstances of the case. It had been objected that the more mod&n type of floating dock should have been adopted, and special reference had beezl made to Mr. Edwin Clark's HydraulicLift dock, buthe thought such objections were without foundation. The land surrounding MaltaHarbour was, for the most part,high and rocky, with a verysmall portion of that low lyingland which rendered the system of Mr. Clark so peculiarly applicable to the banks of thel'hames, and to an extensive commercial trade.The great advantage of the hydraulic liftwas, that by means of it a number of vessels could be floated off of it on pontoons into a shoal-water pond or lagoon; the only limit, so to speak, of thenumber of vessels being the time it took to lift and remove them, and the area of accommodation inthe lagoon. In the operations of cleaning the bottom and painting, a vessel on a pontoon had an advantage over one in a graving dock, owing $0 the greater ex- posure to the Cirying action of the wind. The proposed dock was not, however, intended for a large con1merciaI fleet, but for a linlited number of iron-clads. He had seen a vessel docked in the graving dock built from the designs of the late Mr. Scamp, and he considered it to be very available and useful for the purpose. Mr. STKPHEXOX,Vice-President, remarked thathe was par- ticularly fadliar with dock co~~struction,and had paid a good deal of attention to the mechdnical appliances for opening the gat.es. As far as he could judge, from a cursory observation of the model of the moving machinery, the power was given outfrom the handle, as seen in the model. It seemed to him there were several matters in respect of suchan arrangement which requiredexplanation. In the first place, the power was given out at right angles, by means of a longitudinal shaft. If the handle had been placed on the shaft, it seemed probable that the whole power could have been at once applied to the main shaft direct; and this seemed, in the absence of further information, to be preferableto any kindof bevel- gealing, whichwas the most costly and dangerous, as far as breakage was cuncelned, that could be applied for the purposes of trans-

Downloaded by [] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. THE SO3IERSET DOCK AT SIALTA. 37 L mitting power. This was 'especially the case in cotton factories, where there was no class of wheel so liable to breakage as bevel wheels;and he could notunderstand why that plan had been tdopted in the present instance. TheGwynne pump was one t,hat could be, and was, largely employed for special purposes;but it was a serious question, whether it wasthe right one to use in conjunction withthe compound marine engine,now being made for vessels under- t,aking long voyages ; though for short voyages it was very . suitable, In engines that h0 was now building for verylarge ships,he found it essential to keep the old-fashioned pump in addition to the new one, in case of the breakdown of the latter. It wasonly fair to my,that the Gwynne pump had the advantage over the ordinary pump attached to the engine, of getting up a vacuumin the condenser before the main engine started. €€e believed the Gwynne pump had been, in most cases, unfttirly used, especially inlong ocean voyages. He knew that for t.he purpose of condensing the steam in the condenser, a Gwynne pump had been started working at Liverpool, and had never ceased t,ill . the ship arrived at Calcutta, except in the event ofsome mishap to, or break-down of the vessel. The advantage of this pump was its high velocity of working ; but when machinery had to travel at a high velocity for weeks together, it was impossible for any engine-man, however experienced and clever he might be, to see that all the parts were kept in proper repair ; and that was the case with the Gwynne pump, when it was worked for weeks or monthstogether. A locomotive might be run from London to Hugby, or 50 or 60 miles further; but after it had traversed, say 200 miles, it became aquestion whether or not it would break down, and the moving parts could not be examined. So with the Gwynne pump,which moved at a higher velocity than a locomotive. Mr. W. H. ALLEXsaid, Mr. Stephenson's observations had reference rather to the work of the pumps in connection with condenea- tion in marine engines than to the work performed at this dock. The former were small engines driven at a high velocity. Pumps of large diamet,er gave out a considerable percentage of duty. The greatadvantage of thecentrifugal pump was its cheapness. Other descriptions of pumps for doing the same work at the Malta dock mould have cost ten times the money. Mr. J. GRANTobserved, in reference to tile mortar and puzzuolana used for the dock, that the strengthof both in sea water was given : and increased wit,h age, as ought to be the case with good mortar. 2uL' Downloaded by [] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. 372 THE SOMERSET DOCK AT MALTA. In one series of experiments beginning with a breaking weight of 154 lbs., at eighteen days the strength increased to 345 lbs., and even 4i2 lbs. at the end of sixty-one days. The testing samples appeared tohave been taken,in most cases, from themortar actually used. In only a few cases did the experiments appear to have been made with mortar prepared for the purpose. Had the Author been present, he would have asked whether some economy might not havebeen effected had itbeen possible to get thecaisson ready earlier, and shut out the water from the excavation, which hadapparently to be done undergreat difficulties. The work would probably have been kept dry at a smaller expenditure for pumping power. Lieut.-Col. A. CLARKE,R.E., C.B., observed t,hat the subject of graving andfloating docks, and of hydraulic lifts, had been exhaust- ively discussed at the Institution a few years ago. He was not an opponent of either the floating dock or the hydraulic lift ; and he had built, for special purposes, the largest floating dock in the world, and had advised her Majesty’s Government to encourage, by a loan, the hydraulic lift at Malta. He therefore trusted he should not be considered wedded to the old system. But the necessities which had arisen with regard to Bermuda (where a floating dock was employed), and which also suggested au hydraulic lift in the commercial harbour at Malta, did not apply to this particular case. The Engineer inthese matters was, to a great extent, in the hands of the shipwrights; and for the ships of large size and tremendous weight of many of those in the Royal h’avy, it was not considered by the shipwrights that the hydraulicsystem would be applicable. One of the objections raised to theold form of graving dock was the advantage which it was said the hydraulic lift had, viz., that with it numerous vessels could be liftedand placed on trays,which could not be done in a graving dock. Thatwas not the case. The graving dock could be made available for placing ships on trays just as well as the hydraulic lift. The trays had only to be placed in the graving dock, and the ships upon the trays, as upon the ordinary docking blocks ; and thus the ships could be trans- ferred to trays as well in the dock as by the lift. The difficulty indealing with the tray system-which was reallythe most prominent advantage of the hydraulic lift-was that of shoring heavy ships. Shipwrightshesitated to limit themselves, for heavy ships,to thebilge shores, andto shoring at the seve1.e angleswhich were entailedby the trays, where breast shores could not be used, ancl until that difficulty was overcome the application of thehydraulic lift could not be established. Be-

Downloaded by [] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. THE SOMERSET DOCK AT NA.LTA. 373 sides, it was essential thatthe dock destined for damaged and wounded shipsafter action should admit of the vessel being docked immediately, andthat this should be practicable under all conditions of weather. In the consideration of thc question of thehydraulic lift, it occurred to himthat there were days when a ship could not be got upon a lift;and that circum- stance, conlbined withthe fact of his being unableto com- manda sitein Malta inwhich it was certainthat, under all conditions of weather, ships could be lifted with safety, led hinl ultimately to abandon the idca of a floating dock as well as thc hydraulic lift. It had been stated that t.his dock was expensive, in comparison with docks elsewhere. An hydraulic lift, to havc done what this dock could do, would probably have cost considerably more than this dock had cost, and would not have had its peculiar advantages. With regard to the selection of the site, between the Dockyard and the French Creek a peninsula rose up from 70 to 90 feet high, and it was argued that by levelling that rock to 5 or 6 feet above the water level an amount of excavation, which cost from &35,000 to 520,000, had been required, and that this expense might have been avoided. But therewere local as well as strongpolitical reasons which rendered it necessary that the present, and, as he considered, most favourable, site should be selected. He was tied by this fact--the French Creek was, when he selected the site, the home and refuge of the whole of the commercial navy frequenting Malta, and this had, bya previous arrangement, to be turnedout of that creek, and sent to seek a resting-place in the Grand Harbour and the Marsa. And as he could not touch the water of the French Creek till the Marsa was ready for the reception of the vessels, the construction of a dock in the French Creek would have been post- poned for three orfour years, had heselected a site for it encroaching upon the water space of that creek. Another dock had almost been commenced inthe north-west basin at theharbour extension. The objection to that was, that whilst the naval establishment was in the Dockyard Creek, this dock would have been a great distance from it, and close to theGrand Harbour, where the merchant shipping would all be. There would have been constant chances of difficulty and collisions withthe mercantile navy, besides the absence of economy, as the dock would thushave been at a distance from the Government sources of manufacture. On the site of the present dock there was at that time a fortifica- tion, but he attached little value to the fortifications : they were obsolete and useless, and hewas perfectly indifferent totheir

Downloaded by [] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. 374 THE SOMERSET DOCK AT M.4LTA. destruction.Again, vessels coming intothe French Creek from the Grand Harbour could steam directly into the dock without getting out a hawser, and without any difficulty, the dock being at a convenient angle to the line of the stream. He had placed the dock so far inland to get it as near the old dockyard as possible, and to secure, when a ship came in, that she should be in still water, and also to obtain wharfage space along which her Majesty’s ships might lieoutside the dock. He did not claim anything new in the section or form of the dock. He believed it was good, and he .did not advocate changes as longas old things were good. Jt was, however, one of the largestand deepest docks inthe world, theordinary depth of water being 33Q feet over the sill. An opinion had been expressed that if he had placed the caisson in position earlier the work would have been less costly, because thepumping, it was assumed, would have been less. Butthe fissure through which the water came, instead of being in line with the length of the dock, traversed across it, which enabled him to control the water better than ifit had traversed the length of the dock ; therefore there would have been no economy in putting the caisson in place earlier. No doubt, as compared with some of the docks in the Thames and in theMersey, the dock was an expensive one; but there was a vast difference between building a dock in a depth of only 22 or 24 feet of water, and where there was a depth of 33 feet. The greater the depth of the dock, the greater was the expense of the pumping. He now regretted, however, that he did not first sink a well, and put up powerful pumping engines. What tended in a great degree to make the workexpensive was the maintenance of eight or ten small engines tokeep the water down. If he had at first erected a permanent well and engines, he believed the expense of the dock would have been considerably less ; for while the total cost of the dock and entrance was about S150,000, the charges for temporary pumping and othermachinery, exclusive of labour, amounted to 28,500, for coal 220,000, and for oil $1,600 ; so that a largeportion of the expense was incurred in dealing withthe water. Generallywhere works of thiskind were to be undertaken in connection with water, the first expense, large as itmight be in applying pumping power of a permanent characterwithout adopting temporary expedients,was thebest economy. Another matter, whichrendered the works apparently costly, was the difficulty of getting rid of the materials from tbo axcavations. In an island of limited extent like Malta, ground for clepositing kpoil was hard t.o obtain. He l1nd either to convey in Downloaded by [] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. . THE SONERSET DOCK AT MALTA. 375 barges the debris to sea, or to cart it away to a distance at great expense, The cost of removal by barges to sea alone was %10,000. He afterwardsinduced the IslandGovernment to grant him ground, where the whole of the remainder of the debris was carted, at the cost of 59,000 more. These were difficulties met with in dealing with a military port; and all the peculiar circumstances of the case must be taken int,o consideration, before a judgment could be pronounced whether the works were costly or not. The general reason which led him to adopt the sliding caisson was, that while the first cost of the caisson was greater than that of gates, with the sliding caisson in docking a ship the people engaged had only one thing to look after. Floating caissons en- tailed a number of people to look afterthem, and after the ship too. With sliding caissons, the cambers and stops could not always be kept entirely free from mud; and in the case of those caissons, the sea must be tolerably free from mud and kindred deposits. At Chatham, with the muddy watersof the Medway, he had not used these caissons ; but while the expense wasin thefirst instance, no doubt, greater, because the cost of the additional camber and machinery was greater in the firstinstance, the difficulty of working thecaisson was veryconsiderably less than thatof the ordinary ship caisson, which took twenty-five or thirty minutes or more to manipulate, whilst this caisson was taken out and put back into place in less than five minutes. It was easily handled and readily repaired on the spot. It also formed the best system of roadway, capable, if necessary, of carrying a railway train upon it, besides other advantages.