[Read before the Wellington Philosophical Society, 13th October, 1873.]
The slip consists of a set of ways, upon which is placed a carriage or cradle running on wheels. The carriage is constructed suitably for hauling up or lowering away ships, motion being given to it by means of a winch or set of geared wheels, hauling-up and lowering-down chains being attached thereto; and the whole is set in motion by means of two 25 horse-power horizontal high-pressure steam engines, placed in position for the purpose.
The ways or rails are manufactured of cast iron. The centre way (which bears the greater portion of the weight of a vessel when being raised) is of the section of two ordinary E girders, connected together at their top tables and other points, two rails 2 ft. 6 in. apart from centre to centre being cast on the top, and two racks to take the palls as a vessel is being hauled up to
prevent the carriage running back. The outer ways are of the section of an ordinary I girder, with a rail cast on the top. The distance apart from centre to centre of outer ways is 30 ft., the ways being kept to their proper gauge by means of cast iron stays placed at intervals of 18 ft., and bolted to the ways. The ways are cast in lengths of 9 ft., the faces of meeting, or ends, being faced or planed so that a correct joint and continuous bearing surface is produced, each length being bolted to the other by bolts passing through the end flanges. Above high-water mark the ways are bolted to sleepers of hinau or totara 12 in. X 10 in., the sleepers being 3 ft. apart from centre to centre, the centre sleepers being 6 ft. in length, and the outer ones 3 ft. The greater portion of the surface consists of rock, which was excavated to the required depth to admit the sleepers and ways, which, after being accurately levelled and graded, were grouted in with Portland cement, and the ground levelled up to the bottom of the rail with rubble. In one or two places the ground was too soft to carry the ways with safety in this manner, and in these cases piles were driven to depths varying from 5 ft. to 15 ft., to which the sleepers were secured. Below high-water mark the ways or rails are bolted to cross sleepers of totara, 33 ft. in length and 12 in. x 10 in., at intervals of 3 ft. centres; four piles being driven under each sleeper, until a depth of 14 ft. of water at high tide was reached. This depth being sufficient to allow 8 ft. of water over the carriage, it was not considered necessary to extend the piles beyond this depth, as a large vessel would weigh very little on the carriage when drawing this amount of water. Beyond this depth, four longitudinal timbers were laid under the sleepers, two being under the centre rail, and one under each of the outer rails. Where the contour of the bottom of the bay differed from the inclination or gradient of the ways, cast iron stanchions or columns are introduced between the sleepers and the ways. The whole of the timber is covered with concrete to protect it from the ravages of the worm.
It was contemplated when the slip was designed, that the site on which it was to be fixed would be sufficiently solid to carry the ways or columns without the intervention of sleepers. The cost of the material would have been considerably reduced had the exact nature of the bottom been known when the design was prepared. The actual weight per foot run of ways and stays, or distance pieces, is about 7 cwt., and to this has to be added the weight of the columns or stanchions, as well as the bolts and other fastenings.
The total length of the ways laid down is 1,050 ft. The gradient, or inclination, is 1 in 23. At the end of the ways, a stop is fixed in the centre line to prevent the carriage from over-running the rails when a vessel is launched. The carriage or cradle is 250 ft. in length on the centre beams, and is made in two pieces; the principal length, which is 180 ft. long, being sufficient to accommodate the class of vessels now frequenting the port of
Wellington. The second length, of 70 ft., is shunted off the ways, but can be attached in an hour or two when it is required to raise a long vessel. The object gained in disconnecting the two pieces, is the saving of wear and tear and waste of power in hauling up and lowering this extra length of cradle, which is not required for any vessel not exceeding 200 ft. in length. The weight of the cradle is about 200 tons, and that of the part detached about 60 tons. The centre longitudinal beam consists of a double line of 18 in. x 12 in. iron-bark timber, made into continuous length by scarfing each length of timber together, the scarf being secured by wooden keys and a scarf plate on each side ¾ in. thick; distance pieces are fixed at intervals of 4 ft. to keep the two beams at their proper distance from each other. The outer beams are of 18 in. x 11 in. iron-bark, secured in the same manner at the scarfs as the centre beams, while the width between the centres of the outer beams is 30 ft., corresponding with the width of the ways.
The wheels are of solid cast iron, each wheel having a 2–¼ in. wrought iron shaft cast in, and are 1 ft. in diameter; the wheel carriages, also of cast iron, being secured to the longitudinal beams with four 1–⅛ in. bolts. There are sixteen pall carriages fixed in convenient positions on the centre beams, to allow the palls to fall into the rack cast on the centre ways; cranked bars and triggers are fixed to allow the palls to be freed under water, after a vessel is placed on the carriage. The power to raise a vessel is applied to the fore part of the centre beams, a pulley wheel 4 ft. in diameter being fixed suitably for the chain to pass over; the wheel works loose on a shaft of 5 in. diameter. A cross beam, made of two pieces of iron-bark 16 in. x 8 in., is fixed across the lower end of each length of the carriage; two strong diagonal struts are also fixed from the centre to outer beams. These beams and struts serve to keep the outer longitudinals in their position when a vessel is being raised, the fore part of the outer beams being kept to gauge by iron rods crooked at each end and dropping into a socket. On the longitudinal beams are placed the bilge beams, or slide beams, formed of a suitable shape to take the bilge of a vessel, being of a depth of 1 ft. over the centre beam and 2 ft. over the outer beam; they are secured to the outer beams by means of iron brackets and cotters, and to the centre beam by means of an iron catch fitting into one side of the slide beam, in the shape of a mortise and tenon in wood work. A space of 8 in. or 10 in. is left between the beams, which is filled with wedges fixing the slide beams firmly in the catches. The slide beams are 15 ft. apart from the centre, there being twelve slide beams on each side of the carriage. At the end of four slide beams on each side there are sockets in which standards are placed for keeping the ends of the ropes used for working the sliding blocks and palls above water. The sliding blocks work on the top of the slide beams, and on to these blocks pieces of wood are secured with dogs to suit the bilges
of the vessel to be raised. Small blocks or pulleys are fixed in positions to guide the ropes in the proper directions, both for the sliding blocks and the palls.
The steam engines for working the slip consist of two 25 horse-power horizontal high-pressure engines, manufactured by Messrs Appleby Brothers, of London. Steam is supplied to the engines by two single-flued circular boilers, 30 ft. in length and 5 ft. in diameter. They are erected in a building about 50 ft. distant from the engine house. The reason for placing them so far distant was to avoid the expense of a heavy cutting that would have been required to place them close to the engines. It is not found that any loss is sustained beyond the expenditure of steam necessary to warm the steam-pipe in the first instance, the steam-pipe being, of course, covered in with hair-felt. The boilers are supplied with water by means of a Giffard's patent injector, but can also be supplied by the pumps attached to the engines; the usual pressure gauges, safety-valves, blow-off cocks, etc., being also fixed. The boilers were constructed at Messrs. Kennard Brothers' works at Crumlin, being sent out to the colony in sheets, and rivetted together on the work. They were tested, by hydraulic pressure, to upwards of 100 lbs. to the square inch before being set into their places in brickwork; the usual pressure at which they are worked when a vessel is being raised is 45 lbs. to 50 lbs. to the square inch.
The engines are attached to a train of wheels, or winch, which, when working in slow purchase multiply the power of the engines seventeen times, while a quicker purchase multiplies the power of the engines nine times. There are seven cog-wheels in the winch, the last and largest being fixed on a shaft of 14 in. diameter, on which the chain wheels work; the wheel for the large chain being 7 ft. in diameter, and for the small chain 9 ft. These wheels are loose on the shaft, and are put in gear by means of a clutch worked with a screw and hand-wheel. The chain wheels are grooved to take the chain, having suitable teeth cast in the groove for each alternate link of the chain to bear upon. The hauling-up chain is 1,700 ft. in length, and made of iron 3 in. in diameter, each stud link being 18 in. in length. For small vessels of 500 tons or under, this chain is worked single, being shackled round the pulley wheel at the head of the cradle; but when it is required to raise a large vessel the chain is worked double, the return end being secured to an anchor block fixed in a suitable position near the winding engine. The small chain, or lowering-out chain, is of 1 ¼ in. iron, one-half being made in long links to suit the teeth of the wheel, and the remainder in lengths of ordinary short-link chain shackled together. This chain is secured in the form of an endless chain, both ends being shackled to the head of the carriage. A pulley wheel is fixed at about 165 ft. from the outer end of the ways, round which the
chain is passed, returning round the wheel of the engine, the lower part passing out below the engine frame through a cast iron pipe 12 in. in diameter. This small chain, whose length is about 1,800 ft., serves to haul down the cradle and large chain under a vessel and to haul up the cradle after the large chain is freed, when a vessel is launched. The total weight of the two chains is about 70 tons, the large chain weighing 62 tons.
For communicating with the vessels being placed on the slip, a wharf or jetty has been erected on the east side of the slip, extending out for a length of 500 ft., there being 22 ft. of water at the outer end. Its piers consist of cast iron frames, each frame having four uprights, a large flat shoe being cast on the foot of each upright. They were bolted together on the cradle of the small slip, and, when lowered out into the water, were picked up by a punt and lowered into their proper position by the side of the slip. The spans are of 35 ft. centres, the beams being of iron-bark 16 in. x 8 in.; but for the first 120 ft. the spans are shorter, the beams being of totara or hinau, and only 12 in. x 10 in. The beams are braced together, and planks nailed on crosswise.
Before commencing the erection of the slip, soundings were taken along various lines into the bay, the line ultimately selected being nearly S.E. by S., on the centre line of the ways. I may here mention that the site for the erection of the slip was moved from that originally proposed. Among the objections to the proposed site, I may state that it was on an exposed spit of land open to the full force of the wind through Evans Bay; the land was sandy and flat, and to carry the ways above high-water it was proposed to build brick arches to the gradient of the ways. The height of these arches above the surface of the ground at the head of the ways would have been 10ft. or 12ft., and adding to this the height of the ways and cradle, the keel of a vessel when at the top of the ways would have been some 17 ft. above the ground surface. A large expenditure would have been required in earthwork to raise the level of the ground to this height, or else very expensive framing for scaffolding. The vessels on the slip would also have been in a very exposed position. The bottom on which the slip would have to be laid was sand or fine gravel throughout. The site selected presented the advantage of a more solid bottom, it was in a less exposed situation, being entirely sheltered from the northerly winds, and more sheltered from those in the opposite direction. It will be remembered that the only winds that blow with any force in Wellington are from north and south, or N.W. and S.E. The line of the slip is well situated, as the wind blows in the direction of up and down the slip. The ways on the site selected were laid above high-water mark in a cutting, in place of on a bank, the cutting varying in depth from a few inches near the water level to upwards of 30 ft. at the top where the engine-house is erected. Below high-water mark the bottom, for a considerable distance out,
was rock, nearly the whole width of the ways; on one side, however, the rock dipped below the surface some few feet.
After the centre line of the slip was set out, sighting poles were erected at various distances up the hill at the head of the slip, and also on the opposite side of the bay, at the distance of about three-quarters of a mile; the centre line could, therefore, be readily checked at any time, and the poles serve to direct a vessel when going on the slip.
The material from the excavation served to reclaim portions of the beach about the site of the slip, forming available ground where strips of sand and swamp previously existed. On the completion of the excavation, the work of laying the ways was proceeded with. The process above high-water mark was exceedingly simple. A traveller was erected over the ways at high-water mark, which was moved up the cutting as the laying of the rails progressed; the sleepers were bolted to the ways before being placed, and, the ground being excavated, the whole were placed in position together by means of the traveller. Four men only were required to carry on this work, viz., two labourers to excavate for the sleepers, and two mechanics to fit up and fasten the ways and sleepers in position. Each length, as placed, was levelled by means of a spirit level and straight-edge bevelled to suit the gradient of 1 in 23, the centre line being checked periodically with the distant sights with a theodolite. The traveller used for laying these ways afterwards served to erect the carriage, which was erected in its place on the ways. Simultaneously with the work above high water, the work of laying the ways below high-water mark was proceeded with—a much more tedious and difficult operation. At high-water mark a frame was erected across the ways for conveniently lifting the different parts on to the small carriage used for lowering the various lengths out below water, until a depth of about 6 ft. of water was reached; the ways were placed in position by means of a traveller working on trestles placed on each side of the ways. A work that occupied considerable time, and proved a much greater expense than was anticipated, was the excavation of the rock below water. The excavation was effected during low water as far out as possible, and the diving bell was then got to work to excavate and remove the remainder. The bell was worked between two punts; the engine and air pumps for supplying the requisite air and driving the piles, and also two pile engines, were fixed on the punts. The men in the diving bell worked in shifts of four, five, or six hours, as circumstances required. This work could not be carried on during the night, as no means could be adopted to correct the levels of the bottom in the dark. If too much had been removed, greater expense in fixing would have been incurred, and more concrete required, without calculating the loss of time; while, on the other hand, if too little had been taken off, great difficulty would have been caused in
clearing away the ground under the sleepers. The mode of raising the earth was by means of a shallow iron box, which was pushed out under the bottom edge of the bell as soon as filled, the box being lifted on to the punts, and the material thrown into a boat and removed. A rope was attached inside the bell to enable the box to be pulled in to the bell again when emptied and lowered to the bottom; and a trigger, or piston, passed through the top of the bell, afforded means of signalling when it was necessary to raise or lower the bell with the rise and fall of the tide.
So soon as a length of 18 ft. of ground had been cleared and levelled by means of the bell, piles were driven in their proper positions under the sleepers; they were cut off to the length required, and driven down their full depth, in order to save the expense of cutting off the piles under water. To drive them, a dummy pile, of the requisite length of the same section as the pile to be driven, was used; strong angle irons were placed on each corner, projecting about 3 ft. beyond the lower end, and were secured with iron straps and bolts. The angle irons being loosened, the head of the pile to be driven was inserted between them, the irons, or guides, being screwed up tight, thus securing the head of the pile in its proper position. The pile was then dropped into its place, and driven down to the required depth. When driving piles, two pile-engines were kept in use; the pile being fixed into the dummy one, while the other was being driven down. When down to the required depth, the dummy was lifted off with the steam-crab, which was then available to proceed with the pile on the second engine. As the water deepened it was found necessary to provide some means to guide the point of the pile into its proper place, and this was effected by means of L iron frames placed on the small carriage used for lowering out the ways. These frames were made to run on wheels bolted to the sides of longitudinal beams, cross pieces being fixed 3 ft. apart on the frames, through which a bolt was dropped into a hole in the beam to keep it to its proper gauge. When it was required to drive piles, this carriage, with the frames on, was lowered out to the end of the ways already laid, the diver being stationed below at the same place; a pile being ready to drive was then lowered down to the diver, who, having placed the iron frame to the required distance, guided the pile in between rollers provided for the purpose at the end of the frame, and then dropped it slowly on to the ground; on one blow being given to it, the rollers were removed and the iron frame pushed back clear of the pile, the diver then proceeding to place the next pile in position.
On the completion of a length of piles sufficient for 18 ft. in length of ways, the carriage was pulled up out of the water, and a section of the ways and sleepers built together on it ready for lowering into its place, the sling chains being fixed in place and buoyed with a small rope and buoy to enable them to
be picked up when the carriage reached the end of the ways already laid. Before a length of ways was lowered, the next section was fitted to it and bolts tried through the holes, so that the diver had no fitting work to do under water. On the section of ways being picked up, the traveller was run out a sufficient distance and the section of ways, sleepers, etc., dropped as nearly into its position as possible; the diver then unfastened the rope with which the carriage was worked, and attached it to a long hook made to pass through the flange of the section being placed, and the section already fixed on the rope being hauled in by the crab which worked the carriage, the two flanges were drawn up close together. The diver then secured the flanges together by means of a vice at each flange. The section of 18 ft. in length (the total weight of iron and timber in the same being some eight or ten tons) being thus approximately in its position, the next operation consisted in levelling it to the gradient of the ways and checking its position on the centre line. To enable the end of the section to be lifted after being released by the traveller, four iron brackets were bolted temporarily on the outer flange before sending down the carriage; under these brackets the diver placed four screws, like wool screws; the carriage was then lowered out over the section of the ways to be levelled. Iron bars, cut to the proper length to reach above the water, were then dropped through tubes in the beams of the carriage on to the rails to be levelled, and on the end of the last piece fixed. When the water was deep it became necessary to stay these bars together at the top, as the least current or motion set the bars swaying out of the perpendicular, but when four or six bars were braced together there was no tendency to sway. The bars being in place, the centre rail was first levelled to the gradient by means of a spirit level placed on the top of the bars, the diver below raising or lowering the end of the ways, by means of the screw placed under the brackets, as was required. The side rails were levelled to the centre rail by the same means. To further check the gradient, bars of equal length were placed on the end of ways, to be levelled at high-water mark and at the top of the ways near the engine-house, the tops of the bars being proved to be all in line by means of a glass. It was found necessary to adopt this mode of levelling when the weather was too rough to level off a boat. To correct the centre line, a fine copper wire was placed on the exact centre at high water-mark, and a frame with a like copper wire and heavy plumbob was placed over the end of the ways to be corrected. A centre mark had been placed on the end of the iron work before lowering out, and the diver below, observing when the plumbob was in position over this centre mark, signalled to the men above to shift the wire as required. The two wires were then seen by a glass to be in line with the centre mark on the opposite side of the bay, a distance of about three-quarters of a mile. On one occasion only did it become necessary to shift the end of the ways, and then only about 1 in.
On the completion of the levelling and lining, the diver proceeded to wedge up the ways and bolt them together, the wedges being inserted between the top of the pile and the lower side of the sleeper. After the piles were dispensed with, a longitudinal timber was laid on the ground, and the wedges inserted between this timber and the sleeper. The ground surface was, of course, not exactly of the same gradient as the ways, and to ascertain the depth of filling or height of columns required below the rail, the iron frame used for the pile guide was placed on the carriage, projecting over some 18 ft. or 20 ft., and the carriage being lowered quite out to the end of the ways the diver marked the distance between the ground surface and the iron frame on a gauge given him for the purpose. The exact height was thus ascertained, and the thickness of the wedges reduced to the smallest limits. The traveller was dispensed with when the water became sufficiently deep to allow a punt to float over the carriage and lift the section of ways to be placed in position.
Concrete was filled in, covering the whole of the timber to a depth of several inches, thus protecting the timber from the action of the worm, and giving a solid bearing over the whole surface of the ground under the ways to a width of nearly 40 ft. The concrete was mixed in a punt and shot down through a tube to the diver. To the bottom of the tube a length of canvas hose was fixed to enable the diver to direct the concrete to any place required within a small radius, the diver ramming the concrete closely in under the bottom of the sleepers, and the punt being shifted from time to time as directed by the diver. It was found that very little cement was lost in this way, the water being scarcely discoloured. It was also found that a southerly wind set such a strong current round the shore of the harbour as frequently to prevent the progress of the work, the current being sufficiently strong to lift the diver off his legs.
The engine-house is built of brick, and is 45 ft. by 35 ft., at head of the ways. It was necessary to build the back and side walls extra strong, they being required to form a retaining wall to the sides of the cutting, which is here upwards of 30 ft. in depth and very rotten in places. The side walls are built with a batter to give extra strength, the thickness of the wall at the foot being 2 ft. 6 in., reduced by sets-off to 1 ft. 6 in. at the top; the front wall is 2 ft. thick for the lower half, and 1 ft. 6 in. at the upper half; the back wall is circular, and built of a uniform thickness of 18 in.; the walls are 22 ft. in height. The roof is a span of 40 ft., built with six principals, and is covered with corrugated iron. A louvre, 15 ft. x 8 ft., is built in the roof to light and ventilate the building. All inequalities between the back of the wall and the bank were filled in with concrete; there is, however, after heavy rain, a considerable leakage through the walls.
The steam engines are bedded on a totara timber frame, the timber being
24 in. square, a hole being excavated for the fly wheel. The winding engineis bedded on to brickwork, and is secured by several iron bolts, 1 ½ in. in diameter, passing through the brickwork and through strong iron beams passed under the walls and into the rock on either side. A well for the chainis sunk to a depth of 35 ft. below the engine frame; it is 8 ft. 6 in. in diameter, and lined with 9 in. brickwork set in cement and filled in solid with concrete. It was sunk through hard, blue, slaty rock. During the excavation very little water collected, but since completion it has collected more rapidly. The well is now full, and the water is only kept from running over by being discharged by the pipe through which the hauling-down chain works.
The boiler-house consists of little more than a wooden shed built on the boiler setting. It is 45 ft. in length, and 16 ft. in width.
The chimney is 50 ft. in height, and 2 ft. square on the inside; the brickwork is 18 in. thick at the foot, and 9 in. at the top, built in cement.
To keep a supply of water for the boilers, a reservoir has been excavated in the gully, a short distance above the engine-house. A brick wall is built across the gully, and the ground filled in solid between this wall and the back wall of the engine-house. The capacity of the reservoir is about 5,000 cubic feet. It collects the surface drainage from the hills, and any overflow is discharged through a wooden drain passing down beside the engine and boiler-houses into the bay. A sluice-valve is built into the bottom of the wall for cleaning purposes.
To give some idea of the magnitude of the work, I may state, in round numbers, the amount of the various materials used in its construction :—
|Cast iron, etc., in ways and platform||550 tons|
|Winding engine, steam engines and boiler||120 "|
|Carriage, including timber and iron||200 "|
|Excavation below water by diving bell||650 "|
|Timber for foundations||200,000 superficial feet|
|Timber for other purposes||150,000 "|
|Cement, upwards of||3,000 barrels|
|Bricks for engine house, boilers, etc.||200,000|
|Time occupied in erection||Fifteen months.|
To raise a vessel the cradle and large chain is hauled out into the water by means of the endless chain, the cradle being first pulled up a short distance to enable the palls to be lifted out of the racks, the bilge blocks also being prepared to fit the shape of the vessel, the blocks being placed at the end of the slide beams. A water-mark, fixed at the head of the cradle, shows when
it is out into water deep enough to allow a vessel to pass over it. The stem or nose of the vessel is hauled up into the guide on the head of the cradle, which is simply a pair of iron bars bent to the proper shape and bolted on to the cradle. The stern of the vessel being hauled into its proper place, the keel is over the centre of the carriage; the back guides are then lifted up to secure the vessel in its place. The back guides are strong iron bars, working separately on a 4 in. pin, passing through strong uprights bolted to the side of the longitudinal beams at such distances as may be required to suit the length of a vessel. So soon as a vessel is thus fixed in position, the cradle is hauled up until the keel rests its whole length on the cradle, and the bilge blocks being then pulled under the vessel's bottom she is hauled up out of the water, the palls being dropped so soon as the bilge blocks are pulled into their proper position. These palls prevent a vessel running back into the water in the event of its being necessary, from any cause, to take the weight off the machinery, and also serve to keep the cradle in its place when up on the ways.
To launch a vessel, the cradle is hauled up sufficiently to allow the palls to be lifted. It is then lowered, by means of the large chain, conveniently near to the water's edge; the large chain is then released, and the cradle and vessel allowed to run out by their own impetus, taking, of course, the small chain. The mode of releasing the large chain is by knocking the pin out of the shackle which secures the return end when passed round the wheel at the head of the carriage, the pin being made conical for the purpose. The impetus caused by running out generally carries the vessel clear of the cradle, but if, from any cause, the vessel does not run out sufficiently fast to clear the cradle, the small chain serves to haul it into deeper water to clear it, and, the engine being reversed, the small chain hauls up the cradle out of the water.
It is sometimes required to raise a second vessel when the cradle is occupied. This is effected by blocking the vessel already up off the cradle. To do this wooden blocks are placed under the vessel between all the bilge beams of the cradle, and the weight of the vessel taken off the cradle by wedging these blocks up tightly. To allow the cradle to be removed, and to clear the keel of any vessel requiring it, small pieces of wood, 2 in. thick, are nailed on to the keel blocks on the centre longitudinal beam before a vessel is taken up. When a vessel is tightly wedged up on to the wooden blocks, as described, these small pieces are split out, leaving a space between the keel of the vessel and the cradle. The bilge beams are removed by knocking out the wedges and releasing the ends from the teeth on the centre beam, and taking out the cotter pins on the outer longitudinals. The bottom of the vessel being thus cleared of the cradle, it is hauled out from under by means of the small chain; the bilge beams, etc., are then replaced in position, and the cradle lowered into the water in the usual way, the chains working under the
vessel on the ways. To replace a vessel on the cradle, the operation is merely the reverse of that just described.
The time occupied in raising a vessel after it is once fixed securely on the carriage is, in the case of small vessels, about twenty minutes, when the hauling-up chain is worked single. With a large vessel the speed is found to be about 15 ft. or 16 ft. per minute. In this case the chain is used double.
Dolphins, consisting of clusters of five piles, are placed in convenient positions for steadying a vessel going on the slip. At present only three of the dolphins are completed, but three more are to be erected. The piles used for these dolphins are of the jarrah wood of South Australia, which is believed to resist the worm for an unlimited period.