BREAKWATER. The Plymouth break water is a public work on which we justly pride ourselves. It was commenced in 1812, and is formed of stone procured from the shores of the harbour. The quarrying of the stone, the conveyance into the vessels by a railway, the dropping of the stones into the sea by opening trap doors in the vessels, the gradual accumu lation of the vast heap, and the dressing of the surface to the required form, are all remark able operations. The works are not even yet completed; for so late as August, 1850, the admiralty advertised for 130,000 cubic feet of dressed limestone, to be supplied during 1851. The breakwater is a straight line of stone-work with two wings inclined a little towards the north ; the straight portion is abbut 1000 yards in length, and the wings 350 yards each. The width at the bed of the sea Is 300 to 400 feet ; but only 50 at high water level. The upper surface is horizontal, and about 2 feet above high water spring tide. The inner face has a slope of 2 to 1, and the outer face a slope of 5 to 1. The coarse rubble contained in the structure, up to the present tithe, exceeds 3,600,000 tons ; the dressed masonry 2,500,000 tons. Upwards of 330,000 tons were deposited in one year (1816). The works (which were under the late John Rennie until 1821, and since under the present Sir John) have cost about 1,500,0001; and seldom has public money been more advantageously expended.
The breakwater at Cherbourg, which is so honourable to our French neighbours, and which attracted so much the attention of our naval officers on a recent occasion, is briefly described in another article. [Crimthouna.] The breakwater at Portland, now being con structed by Mr. Bendel, will shelter an area of 1822 acres. From the eastern point of the island of Portland, it will run out 1,500 feet in an easterly direction, and then 6,000 feet north eastward ; but at the angle between these two portions will be an opening about 500 feet wide, for the entrance of steamers and small craft. More than 7,000 feet of the entire length will be built in 5 to 84 fathoms depth at low water. From the large store of stone
in the island, the facility of transport, and the employment of convict labour, it is estimated that this great work may be completed for 560,0001. A railway, with three inclines, drums, wire-ropes, &c., are employed to raise and lower the waggons, and to carry stones from the top of the island to the spot where they are dropped into the sea.
The determination of the government to construct harbours of refuge has led to the promulgation of many plans for breakwaters. A few of these we shall briefly glance at, as well as others suggested somewhat earlier.
Captain Tayler's Floating Breakwater was introduced to public notice in 1838. It con sists of a frame-work or caisson of timber, moored and shackled, so as to yield to the violence of the sea, and to admit the water to pass under, over, and through it. The cir cumstances which, to the inventor's mind, seem to point out this as a useful form, are the fol lowing : 1st. It divides and breaks the waves, and reduces them to a harmless state ; con verting all that happens to lie within a crescent of such breakwaters to still or smooth water.
and. It is free from the objections which often pertain to solid breakwaters, in so far at they tend to the filling up or obstrtieting of bar bouth and channels by accumulation of sand and hiud. Ord. It tan be laid dotrn on any part of the coast, so as to form it harbour where none can be formed by ordinakyfileans. 4th. It can be constructed and kept in repair at a mere fraction of the cost of an ordinary breakwater. These are high claims, but they have not yet Met with a favourable reception. According to the specification of the patent, the timber-framed caissons are to vary in shape and form according to the depth and nature of the sea wherein they are to be moored ; but, as a general rule, about one third of the mass is above water. As it is optional to make the structure of any convenient dimensions, many such may be chained or otherwise fastened end to end, so as to form a lengthened straight or curved breakwater.