HARBOR CONSTRUCTION.

Gisborne Times, Volume XXV, Issue 2108, 17 June 1907, Page 3

HARBOR CONSTRUCTION.

REVOLUTION IN BREAKWATERS.

STEADY AND ILDATING STli 10’ STRUCTURES.

The following particulars regarding the Murray system of harbor construction are taken from the latest issue of “Progress” : WHAT IS CLAIMED, By taking advantage of a thing which has “been sticking up in front of the whole world for centuries, the Scottish-American engineer. Hr. E Murray, claims that he has iounti out how to construct floating - breakwaters, floating docks, coal stations, lighthouses, wharves, forts, piers, everv kind of construction known to the art of the marine engineer. He claims for them all perfect stability, as well as absolute safety in the most exposed situations; a comparative cheapness of cost which is phenomenal and must be revolutionary; anu unfailing success bv reason of their immunity from all vicissitudes or the j usual conflicts with the ocean. THE INVENTION DESCRIBED. An American writer in the Shipbuilder describing this invention with force and-clearness, says: “A great basic principle has been discovered, namely, liow to use the enormous water pressure at a depth in the ocean to provide static resistance that counteracts the possible oscitation due to wave action at the surface. By going deep enough down with buoyant jsteel caissons into the tranquil lower waters of the ocean that lie beloiv the comparatively shallow surface stratum of wave disturbance, and by constructing these steel caissons so that they have at their base a wide-projecting and lioavilyweighted flange. On which tile super- , imposed water rests with ponderous weight, exerting at 32 feet below the surface a pressure of 2160 pounds per square foot, or at 60 feeit down a pressure that exceeds two tons per square foot. Mr. Murray in effect secures' a steady floating foundation on which any superstructure, properly designed to minimise the wave blows, may be placed, be it lighthouse, breakwater, -or fortress. Such a foundation opposes the dead inertia of its own wejght and the weight of the water resting upon it, to such a degree, that the wave blows above are powerless to disturb the equilibrium of the. floating body as a whole. It is the familiar principle of the iceberg, but with important improvements on nature’s plan, for there is onlv a light, buoyant air space at the top, nine-tenths of its weight is thrown to the base, and this base itself is widely protected beyond the central caisson, conditions all three of which mark gains towards stability. Thus we attain steady flotation, and can secure for a hundred and one uses decks or platforms rising from the surface of the sea that defy oscillation above because of the static resistance deeper down offered by their motionless and j-igidly connected foundation ”

A FRENCH ENGINEER’S OPINION. -

A writer in a .French magazine, who describes how. he was sceptical at first and how he was easily converted into a strong believer, sums up thus: “The constructions are intended to resis±__all the perturbations which are produced on the surface of the ocean. It might seem at first sight that nqt only are these results impossible to attain, but they are in conradiction with what has been admitted up to the present in oceanography. .However, Mr. Murray has triumphed oyer the difficulties simply by submerging his floating structures to a depth where the waters are absolutely stable and are not subjected to any action by the oscillation of the ocean surface. . It is sufficient to' understand the efficiency of the operation by recallin'- that the' action of the billows on the superstructure is annulled by resistance.-of the deeply submerged portion of the floating structure. The deeper this submersion is the greater the resistance, for the increase of depth, itself increases the weight of the water, with the result .that the lower structures suspended ;in this medium becoaifiS. more and more immobile. This theory is supported ;by numerous demonstrations.” OTHER ADVANTAGES DETAILED Describing a n illustration of a harbor constructed .on the Murray , system Progress says:Inside these- floating structures there is perfectly calnwwater. Thankt to the basic principle, the breakwater and the other structures are doubJj anchored.' First, they, are anchored naturally by the deep water; which so neutralises the shocks of the sea at the surface .that there is no “pull” On the structure; secondly, there art anchored artificially? to the bottom resisting the set or currents, tidal and otherwise. In the second respect the anchorage, these structures have the advantage oyer a floating ship, that they use any number of . anchors that may he desired. As a matter of fact, they are anchored by blocks of 60 tons (or more) of concrete; anchored to the solid rock, practically the rock being of the engineer’s mak-. ing, being part of the construction. How long will they last? As long as steel endures. 'This may be ensur, ed by regular painting of the surface between wind and water, a process easily compassed in fine weather after pumping but the water-ballast in the caissons.' The heavy portion below gets crusted thickly with barnacles and such growths of the sea, which have the ..effect of preventing rust, consequently the more the barnacle: the better for tliejife of the structure:

INDEFINITE EXTENSIONS

POSSIBLE. “When the trade demands extension there is no difficulty at all. All that the authorities have to do is'"to tow the breakwater further, out and building others, as"maty as may he required, to anchor them in the proper places. Of course they need not he continuous, for . with a hundred feet of space between these the big waves,- after passing, tumble harmlessly to pieces. Moreover the- may he anchored irt any formation; line or echelon, or any other, and at angles suitable for minimising the effect Sf-tides and currents. Much of the current passes underneath, it must bejmrrie in mind, and when there is travelling shingle anc'l ;-<ifid : —those bugbears of all modern breakwaters— they pass by harmlessly in the ordinary way as if there were no obstruction at all. Consequently the expense of dredging is avoided, the depths remain constant, there is no injury to the _-foreshore, and the spectacle_so well known at Timaru, let us say, of the battle with the ocean maintained by daily train loads of rubble from the neighboring auarry. run out and dumped into the 4oa. will never he seen. - Thero is another Great- advantaeo: theso floatin'- structures arc out of the reach of earthquakes, and even the tidal wave so often destructive to the solid walls of modern breakwaters mav.pass over their floating substitutes without doing them the least injury,