184S.] 



THE CIVIL ENGINEER AND ARCHITECrS JOURNAL, 



123 



A project was started by the Earl of Courtown, in the year 1847, for add- 

 ing to the lengtli of the pier at the Harbour of Courtown, ou the coast of 

 Wexford, which had proved an entire failure, from the channel between the 

 solid pier being continually choked up with sand. Iron piles, with screws of 

 2 feet diameter, to he driven from II feet to 15 feet into the sand, and blue 

 clay, were decided to be used in order to form an open jetty through which 

 the sand could be washed by the current, and the platform would be used 

 for loading and discharging the shipping. The surf was so heavy on the 

 coast that the usual barges or floating rafts could not be used for putting the 

 piles down — so an ingenious plan was designed by Mr. Mitchell, for project- 

 ing a stage forward from the solid part, rigging a large grooved-wheel upon 

 the top of the pile, passing an endless rope-band around it, and round a 

 pulley fixed 150 feet back, and then, by a number of men hauling upon the 

 band, a rotary motion was communicated to the pile, which screwed it down 

 very fast. By these means one bay of the pier, 17 feet long, was finished 

 daily, even in very rough weather. The entire length of the jetty was 260 

 feet, its breadth 18 feet, with a cross-head 54 feet long, with landing stages 

 at each end, and two lines of railway throughout. The entire cost of this 

 extension was 4,150/., or about 47/. 10s. per lineal yard — an extremely small 

 sum compared with the cost of stone piers ; but even that was more than 

 the expense would be now, as the system of work is better understood, and 

 materials are now cheaper. The account of the difficulties incurred in tlie 

 execution of these works was most interesting, and ample testimony was 

 borne by engineers of eminence, and men whose maritime experience gave 

 weight to their opinion, of the superiority of Mr. Mitchell's screw-piles and 

 moorings over every other system for holding buoys, or for supporting bea- 

 cons and lighthouses, and their use was suggested for the foundation of 

 bridges, viaducts, and numerous railway and other works, as well as a multi- 

 plicity of applications which had not hitherto been thought of. 



Mr. W. A. Brooks gave an account of the method of laying down the 

 moorings at Newcastle-on-Tyne, under his directions. A heavy chain, formed 

 of 3i-inch round iron, in links of 3 feet long each, was stretched along the 

 bed of the river, in the direction of the current. To this chain, beneath 

 each tier, was attached a 2i-inch moorlng-chain, fixed to the head of a screw 

 mooring ; another screw being also placed beneath each tier, and driven 

 down between 10 and 20 feet into the clay, and sometimes full a foot into 

 the shale rock. The screws were 4 feet in diameter, and were placed in 

 depths varying from 15 feet to 24 feet at low-water spring tides. They 

 were screwed down to the depth of 15 feet in an hour and a half, and some- 

 times 21 feet in two hours. Each mooring screw was intended to have 

 borne the strain of four heavy ships ; but, during the last winter, the port 

 was so crowded, that more than double the proper number of vessels were 

 moored upon each ; and yet there were no signs of weakness ; and whilst 

 nearly 30,000/. of damage was done at Sunderland, during a heavy storm, no 

 casualties occurred at Newcastle, which Mr. Brooks stated was entirely owing 

 to the sound holding of the screw moorings. He argued, therefore, that the 

 small sum of 2,500/., paid by the harbour commission of Newcastle for the 

 right to put down these moorings, was a very wise expenditure. 



Mr. T. Smith, Pilot Master of the Port of Shields, corroborated Mr. 

 Brooks's statement. 



Captain Washington, R.N., had, in the course of his surveying duties, 

 seen the screw moorings in almost every position, and had heard them uni- 

 versally eulogised, as being the best and safest moorings hitherto known. 

 He strongly recommended their employment. He had also examined care- 

 fully the screw-pile lighthouses, and had every reason to be satisfied with 

 them, as aftording a means of placing lighthouses and beacons where they 

 were before impracticable, and enabling floating lights to be generally super- 

 seded by fixed lights, which latter he proved, from documentary evidence, to 

 be one-third less annual cost than the former, and certainly more useful to 

 sailors; for, in spite of all the care, attention, and even lavish expenditure 

 of the Trinity Board to moor the lightships securely, they did go adrift just 

 at the time when they were most required. He, therefore, advocated fixed 

 lights in every situation where a foundation could be obtained ; and he be- 

 lieved that, with the screw-pile, there were scarcely any situations where 

 this could not be accomplished. 



Messrs. Walker, Cubitt, Rennie, Murray, Moorsom, Mitchell, Scott Rus- 

 sell, and others, took part in the discussion, adducing instances of the efli- 

 ciency of the moorings and the piles, and of their appUcability to numerous 

 engineering works, for which they expressed their intention of employing 

 them. The high price hitherto charged for the right of using them had 

 somewhat retarded their general introduction ; but it was explained, that Mr. 

 Mitchell had feared to entrust to others the fixing of them, lest a failure 

 might ensue before his system was perfected, which, however, he now thought 

 it was. Now, however, as the right of granting licenses for their use was 

 transferred to men of business who had purchased it, there was no doubt of 

 their being brought within the reach of every application. 



Fei. 29. — The paper read was entitled " Remarks on the Formation of the 

 Entrances to Docks, situated upon a Tideway." By Mr. J. B. Redman, 

 M. Inst. C.E. 



After illustrating the subject by the example of the position and direction 

 of all the principal dock entrances on the borders of the Thames in the 

 port of London — showing that the variation in the opinions and practice 

 of engineers had been very great — the paper detailed the ordinary me- 

 thods of docking and undocking ships, and the precautions to be taken in 

 constructing entrances, which should be best adapted for facilitating these 



operations ; and, although it was difficult to lay down any positive rules upon 

 the subject, as the engineer must, in almost every case, be guided by local 

 circumstances, yet in ordinary cases the following general rules were recom- 

 mended :— For graving docks, an angle of about 45°, pointing up the stream; 

 for wet docks, an angle of about 60°, in the same direction ; and a right 

 angle, with the stream, for building ships. These, it was believed, would he 

 generally found the most available. 



March 7.— In the discussion upon Mr. Redman's paper, the merits and 

 defects of the several dock entrances in the Thames and in other situations 

 were examined, and the general result appeared to be, that although the en- 

 gineer must be guided by local circumstances, vet, that in situations where 

 the river was sufliciently wide, and the position of the land permitted, an 

 acute angle pointing up the stream, was the best for docking vessels with 

 the flood— that the reverse would be best for undocking ships. In ordinary 

 widths of rivers, therefore, the end would be attained by forming a bay sutfi. 

 ciently deep to render the water still in front of the dock, the wing walls 

 being so much splayed as virtually to give the directions up and down the 

 stream as circumstances required. The peculiar positions of the docks at 

 Ipswich, by Mr. Palmer, the alterations of the Duke's Dock at Liverpool, by 

 Mr. Cubitt, and other cases, were sustained in support of the arguments of 

 the speakers, who all united in praising the industry and talent of Mr. Red- 

 man, in bringing forward the subject in the complete manner he had done. 



March 14.— The paper read was " An account nf the effect u/ the Storm 

 of the 6th of December 1847, on the coast near Edinburgh, as iUustrating 

 the Principles of t lie Construction of Sea Defences." By W. J. M. Ra.nkine. 



The principal example given was the sea wall of the Leith branch of 

 the Edinburgh and Dalkeith Railway, built by the author in the year 1837, 

 from j\lr. Walker's designs. Just after it was completed, a violent storui 

 occurred, which injured almost every similar work within ils range, but 

 produced no ill effect upon (hat structure. On the 6th of December 1847, 

 a still more violent storm occurred, which did great damage all around, 

 but the railway wall still escaped without injury. The total length of the 

 wall was about 750 yards ; its height was 13 J feet above the beach at the 

 highest point, diminishing to about 6 feet at the ends. The height of the 

 top was 4 feet above equinoctial spring tide level. Its least thickness was 

 5 feet and its greatest 10 feet; the back was vertical, but the face had an 

 inclination at the lower part of 5 inches in the foot, gradually becoming 

 curved as it rose upwards, until at the top it overhung slightly. The 

 foundation course was composed of large flat stones, laid horizontally 4 

 feet below the surface of the beach, upon a stratum of fine sand and 

 gravel, firm when dry, but moveable when wet. The face was of 

 hammer-dressed ashlar, about 2 feet thick ; the back of rubble, 18 inches 

 thick. The interior was filled with concrete. The coping was composed 

 of stones each weig-hing about half a ton, connected by means of cast-iron 

 dowels. The stone used was Craiylicth sandstone. The face joints were 

 laid in cement for a depth of 4 inches. The foundation was protected by 

 a pitching of trap boulders, laid on the natural level of the beach. They 

 were parlially disturbed by the storm referred to, and the author ascribed 

 this to their weight being insufiicient to resist the vertical oscillation of the 

 waves. 



The second example was a vertical sea wall near Trinity, the fouodatioa 

 of which was protected by a dry stone bulwark sloping at angles of from 

 30 deg. to 40 deg. The wall was injured by the the storm, but the pitch- 

 ing was breached at several points. 



The third example was another wall near Trinity, of a hyperbolic sec- 

 tion. The lower part had a slope built dry up to a Utile below high-water 

 mark. At this point there was a sharp curve, and the upper part was 

 nearly vertical, and laid in mortar. The waves extracted the stones of 

 the curved portion, and ihe upper part, being undermined, was destroyed 

 to a great extent. 



The last example was the bulwark of the Granton line, the lower part 

 of which sloped at about 20 deg. ; the upper portion was curved, and was 

 covered by a heavy projecting stringcourse and parapet. It was built 

 dry, and the stones of Ihe lower part weighed not less than half a toa 

 each. This bulwark sufl'ered damage to a slight exteut on its upper por- 

 tion. 



These examples were stated to confirm the following principles : — 

 That the principal action of the waves in front of a sea wall was a ver- 

 tical oscillation, produced by the combination of the direct and the reflected 

 waves ; that a sloping bulwark gave rise to a sloping oscillation, tending 

 to overturn any portion which projected above the line of slope ; that 

 where the strength of a sea wall depended on the pressure of the super- 

 incumbent masonry, and the adhesion of mortar and cement, the position 

 of greatest stability was vertical; and that when the strength depended 

 on the weight of the individual stones, the position of greatest stability 

 was a very flat slope. 



In the discussion which ensued, instances were adduced of the duration 

 of vertical walls under the attacks of heavy seas, and, on the other hand, 

 of their destruction when flat slopes had etfectually resisted the waves ; 

 and it was agreed that in this, as in all other cases of engineering, no 

 empirical rules should be laid down, but that the skill of the engineer 

 should be exerted to adopt such forms of construction as were best adapted 

 to the locality and the circumstances. 



3Iarch 21. — The discussion ou Mr. Rankine's paper was continued. 

 Letters were read from l\lr. Maclean, describing the iiarras and Piel sea 

 embankments; and from Mr. Macdougall Smith, on the importance o£ 

 using stone of great specific gravity in sea-works. 



17* 



