Another plan recently proposed consists in placing a number of spars upright in the sea, three or four feet apart : the spars being five or six inches square, and of a (hbout 24 feet) sufficient to reach the whole depth of the deepest waves. A heavy stone or any kind of mooring anchor is lowered to the bottom of the sea beneath each spar, and the spar is connected with this by a chain. Each spar yields easily to any forcible pressure from the sea, since the small chain at bottom acts as a hinge ; but it will soon recover its vertical direction, which it maintains by virtue of the wood being of less specific gravity than sea water. How many rows of such spars would be necessary to check the force of' a sea, would in all probability depend_ on the nature of the locality.
Captain Vetch (in Weale's Quarterly Papers, 1843) advocates a vertical construction of breakwaters,, instead of a sloping face towards the sea. His plan consists in a peculiar ap plication of wrought iron rods, which pass vertically through the water, and are supported by horizontal iron frames, through orifices in which the rods pass. The frames and rods receive lateral support by other rods placed in a sloping position, in a double row on the two faces of the breakwater.
In 1848 Mr. IV. H. Smith published a small pamphlet relating to Harbours of Refuge, in which he recommends the use of a peculiar kind of breakwater. It consists of a hollow framework of timber, which is secured to the ground by screw piles, such as those employed in Mitchell's screw-pile lighthouses; the frame work is free to oscillate on these piles, within certain limits, which are determined by mooring blocks, and counterbalance weights.
Captain Sleigh's proposed breakwater con sists of a series of sloping or oblique platforms supp orted by floating hollow vessels or caissons; by which the platforms are always maintained in an oblique position, and are enabled to rise and fall with the tide. These floating vessels and sloping platforms are to be so arranged as to form sea and wind barriers for sheltering ships, pier-beads, and bridges ; they may be made of any dimensions, and any convenient number of them may be ranged end to end, so as to form either a straight or a curved line, according to the size and shape of the spot to be sheltered.
A singular form of Breakwater was suggested by Captain Norton a few years ago. He had observed, that where the lotus plant grows on a lake or pond, if a strong wind ruffles the water on one side of the leaf, the water is com paratively smooth on the other side : resulting from the wind having no hold on the broad expanse of the leaves. He had also observed, after a storm at sea, the solid timbers of a wrecked vessel splintered in pieces by being driven against the shore ; while a wicker basket escaped uninjured. These two facts suggested the idea of constructing a floating breakwater of osiers. A model of such a machine was ex hibited at the Polytechnic Institution in 1843.
Engineers of eminence, both military and civil, are at present engaged in a discussion whether vertical or sloped faces are best for sea walls and breakwaters. So much is this an undecided question, that the recent injury to the new works at Dover Harbour is ap pealed to, to afford evidence on one side or the other.