HARBOUR DREDGE

Evening Post, Volume CXIV, Issue 50, 27 August 1932, Page 23

HARBOUR DREDGE

WHAKARIRE DESCRIBED

MANY YEARS' SERVICE

Although Wellington is fortunate in possessing a harbour which does not require constant dredging to keep it open for big ships, among the most useful, in an unobtrusive way, of the Harbour Board's floating equipment is the bucket dredge Whakarire, which has shifted millions of tons of spoil during its 28 years of service. The dredge's activities have been confined mainly to lifting spoil from tho bed of the harbour and depositing it at points around the waterfront where reclamation work has been carriod out, in dredging the sites for new wharves, and in maintaining tho desired depth of water at the wharves after they have been constructed. In co-operation with the Wanganui Harbour Board's suction dredge Kaione, the Whakarire dredged the site for the Floating Dock Wharf.

The Whakarire was purchased by the board mainly to deal with Falcon Shoal, near the entrance to the harbour, which,

with the coming of vessels of deeper I draught than those which visited the' port previously, required to be deepened. For about two years, during much of which time the dredge was working day and night, dredging operations were in progress at the ehoal, until a depth of seven fathoms was obtained. Up till last year the dredge had been laid up for periods aggregating five years, and, while in commission, had worked for 87,255 hours, 23,540 of which were spent in actual dredging, and had lifted over six and one-tjiird million tons of spoil. Four and a half- million tons had been pumped ashore by the dredge into the various reclamations. Although dredges, at first sight, appear to be about the moafc uninteresting of craft, they really possesse many points of interest, and the handling of them is a skilled job. Dredges, in fact, have received aa much attention from ship designers and builders as have most other branches of shipping, and many large firms specialise in the construction. Each dredging job has its own individuality, and can be best done by a particular type of dredge. TYPES OF DREDGES. Some dredges possess no power of propulsion of their own, and have to be towed from place to place, while others, such as the Whakarire, can move about under their own. steam although, for their actual dredging work, they are almost invariably moored in position. Dredges 'such the Whakarire deposit the spoil, they have lifted in their own hoppers and take it to wherever it is to be unloaded, but others- pass it on to "hoppers" lying alongside. The advisability of each system, depends on whether the dredge is self-propelling, and the diatance of a suitable dumping ground from the scene of operations. The Whakarire brings the spoil to the surface by means of steel buckets, the Kaione uses a snetion pump, and other dredges use a grab, while there is . also a primitive spoon type with a spoon fixed to the end of & long pole in much the same way as it was probably used by the Phoenicians and Eomans. The last type, which are known, as dipper dredges, are used more particularly in the United States, where there are some big ones. The class of dredge to which the Whakarire belongs is the most common. The general principle is-that of an endless chain of big buckets working round a "ladder^ hinged at the top and capable of being lowered with purchases to the desired depth. In order to take this "ladder" a deep well is cut in the hull of the dredge, dividing her almost in two. MUCH HABD WEAK. From the top of the "ladder" a rod bevelled at the top to turn the wheel, goes down to the engine room, and with this the endless chain is hauled up. The buckets dig into the sea bed at the lower end, and turn over when they reach the top, emptying out their contents. The wear on various parts of the dredge is very severe. The lips of the buckets quickly become worn though made of the hardest possible armour steel, and the rollers on which the chain is hauled are also liable to heavy wear. The top tumbler, over which the buckets: roll, has to be made of the very finest manganese, or high carbon cast steel. In a report sent to the makers of the dredgo last year, the then chief engineer of the board, Mr. J. Marchbanks. stated that the tail shafts and etern bushes were thoso originally supplied with the dredge, and after so many, years of work without any repairs or special attention, had been referred to by the surveyor as being practically wearproof. The boiler, also, which had not been renewed, was in good condition and was considered to have many years of useful life before it. The Whakarire was ordered in 1902 from Messrs. Lobnitz and Co., Ltd., of Renfrew, Scotland, and -was built under the supervision of Mr. Alex Mac Donald, superintending engineer to Messrs. J. P. Corry and Co. The dredge was launched on 15th April, 1903, and was christened by Mrs. Beachamp, wife of a former chairman of the board. After making the voyage out under her own steam, the dredge arrived at Wellington on 25th October,. 1903. The trip was mainly uneventful, but shortly after leaving Thursday Island the vessel touched and dented the bottom, necessitating repairs when she was slipped to be dismantled from her sea-going condition and to have her dredging gear erected. DETAILS OF MACHINERY. The Whakarire is a twin screw vessel of 819 tons gross and 450 tons net register, has a-length of 180 ft, a beam of 36ft, a depth of hold of 13ft, and a moulded depth of 16ft, The drodging

able of dredging from a depth of 43ft, with a twenty-inch auction pipe capable of lifting from, the same depth, and arranged to work over the starboard side of the vessel. There is a single boiler generating steam for two main engines, each of which is rated at 60 h.p. nominal and guaranteed to exert 250 indicated horse-power. On the propelling trials the engines jointly exerted 575 indicated horse-power. The vessel, with 646 tons of spoil on board, drew lift 7in forward and 13ft Sin aft, and steamed at 7. 17 knots on the measured mile. When light, with empty hoppers, a speed of 7.51 knots was attained. In both cases the outboard suction pipo was in position. This was removed before the vessel left for Port Said, to which port from the Clyde, her speed averaged 7* knots. The dredge sailed from the Clyde on 9th July, 1903, and arrived at Wellington on 25th October after 90 days' steaming, so that the speed was maintained very satisfactorily on the voyage.

The cost of the dredge, delivered in Wellington, including some additional anchors and chains and covering exchange, supervision, and other charges, was-about £39,150. Additional.expenses were incurred by the purchase of 500 lineal ft of 24in steel riveted pipes to be used in delivering spoil from the dredge for reclamation purposes, and a

apparatus consists of 40 buckets, caprapid disconnecting piece, with three flexible connections to be attached to the outlet pipe of the dredge. To enable the anchors in connection with the dredge to be promptly laid down, and to enable the moorings to be picked up promptly, a heavy boat was secured. The Whakarire commenced dredging on Ist December, 1903, off the Glasgow and Bailway Wharves, and in the following year one of her main operations consisted in dredging the site for the construction of the Taranaki Street Wharf. Some of the spoil was doposited on tho reclamations at Clyde - quay and Waterloo quay, and some of it was taken out to sea.. •