T'lymouth Sound or Harbor, being open to the sea, was so much exposed to storms that early in the last century it was determined to construct a breakwater across its mouth, with openings between it and the shore on either side, for the ingress and egress of shipping. The works were commenced in 1812. The operations consisted in transporting along a tram-road large blocks of limestone procured from a neighboring quarry, shipping them in vessels fitted with trap-doors, and depositing them in the shape of a huge mound in the required situation. As soon as the stones began to appear above water, a per ceptible benefit resulted in the relative calmness of the Sound during the prevalence of storms; but the structure was frequently very roughly handled by the waves, which altered and flat tened its shape. A severe storm in November, 1824, threw a great portion of the stones over into the Sound. It was not until 1841 that the works were finally completed by the deposition of inure than 3,000,000 tons of stone, and the total expenditure of nearly $7,500.000. The breakwater is nearly a mile long; the central por tion is 1000 yards; and two wings of 350 yards each extend from the ends of this at a slight angle. The open channels :it each end, between the breakwater and the shore, are each about half a mile wide, and their depth is respectively 40 and 22 feet at low water. The breakwater is 133 yards wide at the base, and 15 at the top, the two sides being made very sloping for the security of the stones. The slopes and top are faced with masonry: The water-space protected by this breakwater comprises 1120 acres.
To convert Holyhead Bay, Wales, into a har bor of refuge. on attached breakwater 7860 feet long was constructed. consisting of a loose stone base capped by a wall of solid masonry about 40 feet high, and, including the 40 feet wallway, about 60 feet wide. The method of construction was to convey the stone quarried from Holyhead Mountain out on a trestle in cars and dump it into the sea until the mound reached the proper height. To form the sea end or head of this breakwater, a masonry platform 50 feet Ivideand 150 feet long was constructed, and on it a light house was erected. The breakwater was begun in 1847 and finished in 187:3 at a cost of over $815 per linear foot. This breakwater incloses an inner harbor of 267 acres and shelters an outer roadstead of 400 acres.
The Portland (England) Breakwater was built to convert the expanse of water between the Eng lish mainland and the isle, or rather the penin sula, of Portland into a harbor of refuge. An act of Parliament was obtained in 1847 author izing the work. The breakwater, starting from the northeast point of the isle, stretches nearly due north for more than 81(10 feet, with one in tertening opening 400 feet long for the ingress and egress of shipping. The works were con ducted more easily than those of any other great breakwater, for the isle contains an abundance of stone easily quarried. and the steep shores afford
ed facility for transporting the stones by their own gravity to their destination. The work, which is an upright ashlar superstructure, with a parapet founded on a mound of rubble stones. was done chiefly b:r convict labor; the depth is about 50 feet at low water. From the nature of the operation, any part of the breakwater be came useful as soon as constructed. The width of the rubble mound at the bottom is 340 feet. This breakwater was constructed between 1849 and 1871, and contains a volume of 4,245.185 cubic yards of rubble stone.
Dover Breakwater, in England, is particularly interesting as being built of solid masonry throughout, the work under water being done by (livers. The interior of the structure consists of concrete blocks and is faced with cut stone masonry. The work was begun in 1817, and in the structure had reached a length of 2100 feet. Since 1893 work has been in progress ex tending this breakwater 580 feet. and in building a second structure of similar type 1500 feet long. The depth of water in which this breakwater is being built is about 45 feet. A conspicuous French example is to be found at Brest, the com mercial harbor of which, completed about 1897, contains a breakwater half a mile long.
Delaware Breakwater for the national harbor of refuge in Delaware Bay (U. S.) is miles long, and is constructed in from 13 feet to 53 feet of water. It consists of a mound of rubble stone rising to low-water level, and above this of a rough wall of very large stones laid in courses without mortar, and with the interstices tilled with small stone. This structure will shelter 552 acres with a minimum depth of 30 feet, and 2:37 acres with a minimum depth of 24 feet, the -combined area being capable of sheltering 1000 vessels at once.
The Sandy Bay Breakwater for the national harbor of refuge at Sandy Bay, Mass., begun in 1885 and still in progress (1901), will be 9000 feet long, and inclose an area of 1377 acres with a minimum depth of 24 feet. Below a point about 15 feet below low water this breakwater consists of rubble stones not exceeding in weight 4 tons each, and above this point it consists of stones weighing not less than 4 tons each, and averaging 6 tons each. The estimated cost of this breakwater is $5,000,000. The breakwater at Point Judith. R. 1., begun in 1890. and still in progress, will be 10,000 feet long, and is esti mated to cost S1,200,000. It is being built of rubble stone to a depth of from 18 feet to 30 feet of water. The proposed breakwater for the deep-water harbor of San Pedro, Cal., will be 8500 feet long, constructed of rubble stone in water from 19 feet to 51 feet deep, and is esti mated to cost $2.901.000.