HARBOUR LIGHTS

Dominion, Volume 27, Issue 151, 23 March 1934, Page 12

HARBOUR LIGHTS

New Beacon Off Steeple Rock BUILT AT THORNDON A Ponderous Structure of Concrete An unusual work of outstanding interest carried out by the Harbour Board’s staff, and now nearing completion, is the construction on the Thorndon breastwork of a large reinforced concrete beacon designed to replace the iron buoy off Steeple Rock on the west side of the harbour entrance near the south end of Worscr Bay. The beacdn is being installed in iesponse to representations by shipping companies and shipmasters as to its desirability as an additional safety factor in working the harbour. The light will give a red flash every second, and will have a range of visibility of six miles. It will be entirely obscured to seaward, and will show through an arc of about HO degrees up the harbour. Vessels entering the harbour on the* leading beacons in the channel will open up the new light just before coming abreast of Steeple Rock, and keeping in its red sector will be able to steer a safe course to a limit of three cables off Gordon Point, where they will open up Halswell Point light. Departing ships will also be assured a safe distance off Steeple Rock, and will be able to give room to incoming ships. Taslt for Floating Crane.

In deciding to build the beacon on shore and transporting and erecting it on the site by means of the floating crane Hikitia, the board’s engineer followed the precedent set in the case of the Jerningham Point beacon, which was, however, a smaller job. That beacon was built in two sections which were placed in position by the floating crane. The Steeple Rock beacon is a much weightier work. Its total weight will be over 100 tons, and as the maximum safe working load of the Hikitia is 80 tons, the beacon has been built in three sections to facilitate its transport and erection. The beacon when completed will be in the form of a reinforced concrete cylinder, surmounted by an accumulator house above which will be the lantern. The focal plane of the light will be 13 feet above the top of the cylinder and 18 feet above high-water level The total height of the cylinder will be 46 feet, while the accumulator house will be an additional 12ft. high the diameter of the top platform, on which tfie lantern will be installed, being 1feet. . , , Due to considerations of weight, the reinforced concrete cylinder has been built in two sections, one 39 feet high and the upper section seven feet high. The upper section, as (veil as the accumulator house, are now practically completed, and have been painted white. The main lower section of the cylinder has the boxing ready for the last “pour” of concrete and when .this has “set,” the ponderous structure will also be painted and made ready for transport to the site off Steeple Rock. This section of the beacon, which is 39 feet high, has a diameter at’ the bottom of 20 feet and at the top of approximately nine feet, its total weight being 75 tons, wholly in reinforced concrete except for a steel ring plate at the bottom where it is shaped to a cutting edge by means of which the weight of the cylinder will force it about three feet into the harbour bed. The circumference of the cylinder at £he bottom is approximately 63 feet. Secure Anchorage. At the site of the beacon, six reinforced concrete piles, each 25 feet in length and 12 inches square, have been driven in a circle ten feet into the harbour bed. their purpose being to “peg” the cylinder securely to the bottom. The big concrete cylinder will b" lifted and transported by the floating crane Hikitia, which will lower it concentrically over the piles, which wifi project well up inside. Concrete will then' be poured in to bind the piles and the cylinder together. The top section of the cylinder will next be secured in position, after which the water inside will be pumped out and the whole of tlie interior filled up solid with concrete. After that, the accumulator house which will accommodate the gas cylinders and otlier gear for the light will be lowered into place and secured to the top of the cylinder, and. finally the lantern will be installed. On one side of the top section of the cylinder, there is a, projecting platfoym which will be fitted with rendering and hooks to enable the board’s launches to moor and lie in security when the gas cylinders are being changed or the light needs other attention. The task of transporting the huge concrete cylinder from Thorndon and placing it in position will be a somewhat ticklish one and will be absolutely dependent on a perfectly fine day and smooth sea. It is estimated that some three hours will be occupied in lifting the cylinder on board the Hikitia. carrying it down the harbour and lowering it into position. There will be just sufficient room on the foredeck of the floating crane for the cylinder, which will be carried upright supported by the main lifting tackle and also by a number of stout wire guys. (Picture on Page 9.)