BLUFF HARBOUR

Southland Times, Issue 20522, 26 June 1928, Page 5

BLUFF HARBOUR

WORK OF THE DREDGE. CLEARING AWAY’ SAND BANK. DESCRIPTION OF ROUTINE. (From Our Correspondent.) The Bluff Harbour Board cannot be accused of neglecting to improve the harbour under its jurisdiction. It has for years realized that the provision of more convenient and safer means of access and egress to and from its wharves is the best manner to safeguard its own interests. For 23 years the dredge Murihiku has been at work in the channel or in any other part of the harbour that required attention.

During that time over 2,068,834 tons of rock and sand have been removed from the harbour and dumped in Foveaux Straits. This means that on the average 90,000 tons have been taken to sea every year.

To Bluff residents the dredge is a familiar sight. It can be seen at any time of the day moored in some particular part of the channel or tied up at its berth at the new wharf. Despite its familiarity, however, it is questionable if any beyond those most intimately concerned with its management and direction are aware of the nature of the work it is doing or has-done in the past. It has been worked right along the main wharf and the depth of water at low tide has been increased from 21 feet to 30 feet, while at No. 1 berth the depth has been increased to 34 feet at low water, so that the biggest vessels that come to New Zealand can be safely tied up there. The Murihiku is capable of dredging 200 tons per hour and has a carrying capacity of 450 tons. After she has taken in a full load she steams four miles out to sea to dump the spoil, this operation taking from one and three-quarters to two hours. Her speed when “full ahead” is from seven and a-half to eight knots. The dredge carries two sets of triple expansion engines. The boiler is 13 feet in diameter, 10 feet 6 inches in length and has a working pressure of 1601bs. The vessel itself is 160 feet long and 35 feet on the beam. She consumes three and a-half tons of coal per day. She is fitted with a sand pump for reclamation purposes and a use for her in this direction will shortly be found when the board puts in hand its proposed works. The pumps are capable of pumping out the dredge in the short period of 20 minutes.

MANNER OF WORKING. The superintendent, engineer and dredgemaster is Mr J. G. Imlay and the navigating officer Captain R. C. Harbord. Under them is a crew of eleven men. After the dredge has deposited a load at sea she returns to the approximate position at which she stopped working, marked by moorings. The slip ropes are passed aboard by two men in a boat and the end is heaved in until all is coupled up. The vessel is then in the same position as when she left to go to sea. The signal is given by telegraph from the bridge that all is clear and the engineers uncouple the propelling gear and put in the dredging gear. When this operation has been completed the ladder (the chain of buckets) is lowered to the correct depth and the buckets start to revolve, in a very short time coming up filled with silt, sand and seaweed. Each bucket holds nine cubic feet and the ladder revolves at the rate of 14 buckets to the minute. When the highest point of the ladder is reached the bucket is inverted and the contents dumped into chutes which convey them to’ the hoppers where they remain until emptied out at sea.

This is done by means of doors fitted in the bottom of the hoppers—four on each side. When these are let go the mud, sand and rock fall out. The water, of course, rushes in and when the doors are heaved up by a winch the water is confined. As the sand and mud, however, are pumped in again this overflows. Air-tight compartments keep her afloat when this operation is gone through.