18S0.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



143 



ON ARTIFICIAL BREAKWATERS. 



On Artificml Bi-eaUwaters, and the Principles- which govern their 

 Construction. By Mi: A. G. Findlay.— (Paper read at the Society 

 of Arts, Lomlon.) 



Mr. FiNDLAv's paper commenced by stating, that it was not wished to 

 pronounce upon the feasibility or inipraetibility of any of tlie numerous 

 plans which have, from time to time, been proposed for the construction of 

 breakwaters, but to submit some facts, drawn from natural effects, sbowine 

 the forces to which such structures must be subjected. 



The paper, therefore, was naturally divided into two parts. The first 

 which related to the action of the waves, and its collateral subjects ; and 

 the second, which was postponed for a future evening, will relate to the va- 

 rious forms which have been given to sea-barriers, and the history of the 

 progress of those now in existence. 



The principal difficulty in establishing a fixed breakwater was shown to be 



the enormous force of the waves. The form and nature of sea-waves ecne- 



rally were alluded to, and Mr. Scott Russell's svstem described. Of the 



dynamic force exerted by sea-waves, it was stated that their greatest force 



was at the crest of the wave before it breaks ; and its power in raising itself 



was measured by a number of facts. At Warberg, in Norway, it rose 400 



feet, January 21, 1820: on the coast of Cornwall it rose 300 feet in 1843 



Other examples, as the singular " Souffleur" at the Mauritius, &c. were 



cited, showing that the waves have raised a column of water equivalent to a 



pressure of three to five tons per square foot; a result in accordance with 



Mr. T. Sevenson s observations with the Marine Dynamometer, which was 

 described. 



It was shown by a fable that the velocity of waves was dependent on 

 their ength; that waves of 300 to 400 feet in length from crest to crest 

 travelled with a velocity of 20 to 27* miles an hour, and this whether thev 

 were 5 or 54 feet in total height ; this velocity alone, should they become 

 primary waves of translation, would give them a great percussive force, 

 tliat waves travel very great distances was instanced by several facts That 

 they are raised by distant hurricanes and gales was noticed, by their beimr 

 lelt simultaneously at St. Helena and Ascension, though 600 miles apart ■ 

 and opinions quoted, that these rollers, or ground-swell, at times originated 

 near Cape Horn, 3,000 miles distant; rendering it more than probable that 

 tropical hurricanes will send storm-waves to our own shores 



That it was not only at their surface that waves exerted great power, but 

 that they reach in their action to the depth of eight fathoms and upwards 

 was shown by the operations for the lecoverv of the treasure of H M S 

 7%e/«, which was wrecked and sunk at Cape Frio, Brazil, in 1831 "The 

 diying-bell was swung four or five feet laterally in calm weather in these one- 

 rauous, much increasing their danger. Besides this, the guns and treasure 

 were found covered by masses of rock of from thirty to fiftv tons weieht 

 moTed by the action of the water, and weighed or turned over in the second 

 operations by Captain De Roos. 



From these facts, it was considered that floating breakwaters generally 

 were not adapted to combat with the waves. Admiral Taylor's plan of 

 timber frame-work sections ; Captain Grove's iron cylinders with an attached 

 grating ; Captain Pringle's frame, moored by its lower edge ; Captain A. 

 Sleigh s floating sea-barrier; Mr. Smith's plan, as submitted to the Society 

 were mentioned; and it was considered that the calculations of their resist' 

 Euce were understated; that Admiral Taylor's section, instead of twentv-five 

 tons strain, might, if the waves exerted only one-third of their for'ce as 

 known, have to withstand upwards of 1,000 tons ; this piobablv caused the 

 failure of Admiral Taylor's experiment at Brighton, and Captain Groves's at 

 Dover. Major Parlby's principle of the trumpet-mouth sea-weed was com- 

 pared with the fucus giganteiis of Dr. Solander, abundant on the Patagoniai 

 arid Fueg.an coasts, and 360 feet in length, which is carried under water in 

 currents, and torn up, and chokes all the bays during storms 



fhe motion of shingle, an important consideration in establishing break- 

 waters was shown to be governed by the direction in which the surf strikes 

 the shore, and this is dependent on the direction of the wind. This from 

 fifteen j^ears observations by M. Nell de Breaute, at Dieppe, was shown to 

 be in the ratio of 229 days from western quarters to 132 davs from eastern 

 quarters, giving that preponderance to its eastward progress.' The mode in 

 which It was arranged on the sloping beach, in the form of a paraboloidal 

 curve, was explaiued. 



corsT'wa,T»t!?ri''^'!! '^"•' '."'f ''''"^'^ "' '''^^"g'"e the character of a 

 part 'oT the Fnl.r?''""f'^ ''I ""'""''' "'"^ "''^'""S t^e eastern 

 western nortinn^TK^n'"^'^""'^ ""<= embarrassed by them than the 

 Txten of'^accn "nb. "^'""d^'" S^-d^ were exhibited as examples of the 

 T.T.^l trlTffT' ""'• ""^ changeable character of sand deposits. The 



fcerhans t'h'e otr^'Ii.'''' P'"«"" "''''''' ''""^«°-' and'were drawn 

 Jrom, perhaps he only authentic history we possess of the changeable cha- 



n 70^/ "l^'f ^?,"^; .Th^ different periods,' from Graeme Spence's su vey 

 ^1/95 down to Captain Bullock's in 1850, showed that they had sliifled 

 ?r^ iole whLrtTlH ''"^"^^■.".i'iently refuting the practicabilitv o any 

 mo?e rflt V fo?h Ir'' f '" ^'""^ '^'"'' '""^ '""^'""S them 'available 

 K! !:tX:^ Commisrn,^18^4r' '' "^' "^"P-^ "^ ^^P»- ^«'='" 



Mr. FiNLAY commenced the second part of his paper by recapitulating 

 some of the forces and circumstances to which breakwaters are subjected, 

 as cited in the former abstract. The application of these was the subject of 

 the present portion. 



„J,^''/?7[9"''"'/?5,"''f ' Cherbourg diyue were noticed; the pro- 

 posals of 1712, and 1777 or a line of sunken ships filled with masonry, as 

 at he siege of La Rochelle ,n 1573, and the first operations by Mde 

 Cessart, in 1/82-4, were described. This latter plan was to sink trunca- 

 ted conical caissons, strongly framed of timber, 150 feet diameter, and 64 

 h'.ts ° Th^fi f ^ ?''"' "^Z ''""'^'^ "'■" "f '"™^"^'= «'-'^ks around their 

 .»t.;.ir/. -i',"''-.?™'"' ""' successfully launched; but before the 



m .r ; ! "^ '", ^ ?■■'"' '^"""Se in the plan ; instead 'of 90 of 



TJLZ '?',l^V^'V'^"''^'y "'^'■^ t° be placed at considerable 

 we e In H f ,;,'"'"■'? '/° ^^ «"^'' ™'"^ pierre perdu; 18 of them 

 were laid, but they were all destroyed but one before 1789,-some of them 



lesorted to, and con inued with until it was modified by an upright parapet 

 from low-water level by M. Dupare, 1832 ; the work is still in progress. 

 The series of four ditTerent slopes, in which the waves have distributed the 

 one of the d,p,e was described ; and the absence of the lowest slope in 

 u on t^ielatter'""' "''' ""^"""'"^ ^°' ^^ *''^ increased force of the waves 

 The commencement in 1811, by Mr. Rennie, and subsequent proceedings 

 under Its present superintendent, Mr. Stuart, of the Plymouth Breakwater, 

 were then alluded to, and the increased length of foreshore which had beea 

 found necessary from the original design, and the greater effect of the sea 

 at Its west end described. In 1S33, from the great effects of a storm, a 

 species of buttress was designed by Mr. James Walker, C.E., for the pro- 

 tection of the base of the lighthouse. This involved a new principle in 

 hydraulic architecture, afterwards alluded to. 



This structure resembles in some degree the system of dovetailing and 

 grooves adopted by Smeaton in the Eddystone; but differs in its application. 

 Ihe Delaware breakwater in the United States was then briefly alluded to. 

 The principle of the presenting a concave face to the waves was then 

 adverted to In 1/34, such a section was proposed, but not acted on, by 

 M. Touros for S Jean de Luz. In 1787-95, Don Tornas Munos constructed 

 the sea-walls of Cadiz thus: a straight foreshore of timber planking, and a 

 curved masonry termination. This was destroyed by the blocks of stone 

 p aced at its foot for protection, rolling up the incline against the masonry. 

 .,' i°.^7^ endeavoured to establish the existence of what he denominates 

 the flut-du.fond, proposed a cylindrical, or other curvilinear face, for this 

 purpose, m 1818, and in 1820 repaired the works of the fortification of 

 St. aiartin, lie de Re, in the Bay of Biscay, on his plan, which was so far 

 successful, though not very greatly exposed. Various forms of the concave 

 rmatement were noticed, and the natural form assumed by the shingle 

 beach vvas cited as an instance of the effect of beach surf. This form has 

 been adopted m the Dymchurch wall, constructed by Mr. Walker The 

 moae of action of the waves against a cliff was also explained, as producing 

 a similar action. ° 



Mr. Scott Russell's deduction from the wave system, leading also to 

 similar conclusions, were then alluded to, and the sectional form he has pro- 

 posed described. He preferred a paraboloidal curve for the foreshore- and 

 an overhanging coping, so as to turn the wave on itself, was described. Mr 

 Russell, for deep water structures, preferred the method h. pierre perdii, 

 forming a straight foreshore. One objection to this system of concave face 

 "^^' tne varying level to which such structures are exposed by tidal influences, 

 and the differences of curve presented at different periods of tide. 



From these systems, the vertical, or nearly vertical wall, was then des- 

 cribed; and the great national work at Dover, the Refuge Harbour, was 

 stated to be on the principle established by the experience of the buttress at 

 the west end of Plymouth breakwater. This mode of construction, found 

 effective at that place, counteracts some of the difficulty met with in securing 

 the masonry facing it. In a previous part of the paper it was stated that the 

 stones were blown out of the facing, or towards the sea wave. This action 

 IS attributed to the percussive force entering the joints, and thus the water 

 or air contained within the body of the masonry being most forcibly driven 

 upwards and outwards, carried single stones out of their beds. The new 

 mode consists of stepping one course of stones into the upper surface of that 

 beneath it, so as to form a ledge to prevent its outward tendency, and also 

 to divert the direct action of the wave on the joint. In addition to this, 

 each stone is so dovetailed on its horizontal plane, that each course forms 

 virtually one stone; and alternate stones in each course are locked into the 

 course beneath it; so that, throughout the fabric, some portion of each 

 course belongs to the one on either side of it, making the whole into one 

 mass. These stones are found at the quarries, and fixed in their places by 

 the diviDg-bell. The situation of Dover Harbour, as being free from the 

 chances of silting up, was considered in reference to the tides, and the im- 

 probability that any great amount of shingle would for the future embarass 

 the work. 



