Thomson's Screw 🌍

Thomson's Screw was name popularly applied to what appears to be a design for a turbine, rather like a wind engine, designed to be placed in the flow of a fast flowing river, to provide motive power to activities such as milling, or raising water for gold slucing or civic supply. It was "invented" by the Provincial Engineer, J. T. Thomson, who produced a working model using the principle (which was in fact not very novel), but when tried on a larger scale, it was found to be ineffective.

Otago Daily Times, Issue 2826, 27 February 1871

Mr J. T. Thomson's model of a machine for utilising the currents of rivers to the purpose of raising water on the river banks, in order to carry on sluicing, supply towns, and provide mill power, was tried at the Water of Leith on Saturday, in the presence of members of the Otago Institute, and worked well. A full description of the system upon which the model is constructed, together with other particulars, is given in Mr Thomson's paper, which appears elsewhere.

THE OTAGO INSTITUTE.

The following "Description of a simple contrivance for economising the current of the Clutha or Molyneux, and other large rivers, for gold-sluicing, town supplies, and mill power," was read by Mr J. T. Thomson, at the meeting of the Institute held on Tuesday last:—

I claim for my present little contrivance some indulgence from the members of the Society while I endeavour to explain its properties and probable uses. By way of preface, I may say that in my report to Government, dated 12th August, 1867, I find I wrote as follows:—
Large sluicing operations would appear to be the ultimate great industry of the interior (of Otago), and that the mining portion of the population have been fuily alive to this will be proved by the enumeration in those reports of their great and numerous water-races.
The principle sources of water are in the Snowy Ranges, and others, the Dunstan, Umbrella, Nevis, Richardson, Pisa, Hawkdun, Eakanui, Rock and Pillar, Lammermoor, &c., &c. But it appears to me that in the Golden Stream - that is, in the Clutha itself - is to be found a power that will serve to wash away all its auriferous banks, and clear the same to the profit of the miner. The fall of this river, from the lakes to the sea is about 1000 feet in 100 to 120 miles, and the area from which it collects its waters above the gorge of the Dunstah is equal to 3,325,000 acres. From these data, we can have a rude or comparative estimate of the power contained in it. Allowing 24 inches of fall over the area by averaging the greater fall in the mountains with the lighter fall in the plains, we have 289,674,000,000 cubic feet per annum as the discharge of the Clutha at the above point. This is equal to a discharge of 551,130 cubic feet per minute, but allowing, again, half the rainfall to be absorbed by evaporation, the actual result will be 275,565 cubic feet per minute.
How to arrive at the object of the enquiry. We have the fall from the lakes to the sea, as above stated, at 1000 feet, which gives 422,500 nominal horse power. This may truly be said to be a very valuable property of the province, which always remains to it, and which, if only partially made use of, may be fraught with great importance to the prosperity of our interior population.
It would not be consistent with the object of this report for me to suggest modes for the economical use of this power; but I may shortly state that I am aware that the mining population have applied it to a limited extent to social purposes. Of all contrivances, however, the simplest, I have no doubt, will prove the most successful, and the merits of the paddle wheel and the marine screw as motive powers will no doubt eventually be much canvassed. I would presumably, advocate the latter, on account of its greater hold on the body of the flowing stream, its ready management and applicability in swift or slow currents, and its easy connection with, the apparatus for raising water.
Since the above report was written, of which this is a short extract, though fully alive to the importance of the subject, I have, owing to constant engagements in other works and services, been able only to give an occasional thought in its direction. Since then I have heard of various attempts by miners and others to apply the force of the current of the Clutha to machinery employed in these enterprises, but how far successful they have been I have had no opportunity of learning. Some years ago I inspected two machines, one of which was for the purpose of raising water, and the other for working the gearing of a dredge, and in both cases the principle adopted was that of the paddle wheel, though one was of unusual construction, being set obliquely to the stream. Neither machine had great power, and having become disused, appear not to have met the expectations of their designers. The paddle wheel, of proper and peculiar form, is no doubt well adapted for driving the machinery of floating mills (flour, bone, saw, &c.) in shallow rivers, where shallowness of the stream would prevent the screw being applicable, and where there was large floatage capacity, at any rate, required to support the mill and its contents; but its great size, cost, and weight of the paddle form of wheel create a most important objection to its general use in the Clutha, where only the temporary works of gold mining for the most part are engaged in. On the contrary, the great depth of the stream is particularly applicable to the screw, working as it does so much below the surface, and when its smallness and lightness make it so easily handled, and its cheapness and simplicity render it of easy construction and repair.
The floating paddle wheel in a seven mile current requires 40 square feet of floatboard to give a power of 12 horses, and of float boards there requires to be eleven in number; while one screw of eight feet diameter would give the same power, and this, instead of requiring to lie floated like the paddle wheel high out of the water by sufficiently strong barges or punts, can be immersed and attached not only to barges and punts, but to a buoy, wire rope, boom, bridge pier, piles, or other fixtures suitable to the various situations.
The Otago sluice head, by the Goldfields Regulations, being equal to 95 cubic feet of water delivered per minute, machines of the above dimensions will raise one sluice head to an elevation of 70 feet, or 7 heads 10 feet, and this without intermission day and night.
The advantage of the screw when made of timber (as I would support) is in its easy construction and repair - this fact should be particularly noted; besides, the screw is the only portion of the apparatus, whether for mills or pumping gear, that need be subject to accidents from floods. Accidents from floods can also be avoided by drawing the screw into the banks till the danger from drifts is over. On the Clutha, with its great body of water, the construction of the screw need not now be scientifically correct, but may be of the rudest description, the fault in form being amply compensated for by the superabundance of power. Thus, the screw may be easily made by a common carpenter and blacksmith - in fact, out of an old gin case and a piece of scantling I would engage to make a very effective 2 horse-power machine. The contrivance then, I am sanguine in stating, supplies that which is wanted by the sluicing, dredging, pumping, and other enterprises on the banks of the Clutha, viz. - an inexpensive and simple machine for economising the power of the current. The nature of the contrivance is simple. A model is now on the table for inspection. I will be happy to show it at work in the stream of the Water of Leith, at any time the members of this Society may appoint, when they could judge of its effectiveness themselves.
The model will be seen to be made of wood, in the make-shift fashion much had recourse to on the diggings, the only portion of it executed by skilled labour being the brass force-pump and india-rubber tubing. The screw (or more properly speaking fan wheel, as the blades in thia little example are plain and not to the helical curve) is 15 inches in diameter. The blades are set to an angle of 20 degrees to the disc, and in a two-mile current the revolutions are once per second nearly. The pistons of the pump are worked by a crank, and, being single acting, propel its contents once per second. The diameter of the cylinder is three-quarters of an inch, and stroke of piston 2 7-10th inches. The quantity of water per stroke is therefore 1.1925 cubic inch. At the above rate of speed, the quantity delivered therefore is 71.55 cubic inch per minute, or 59.5 cubic feet, equal to 3689 gallons per diem of 24 hours. This little model would, therefore, liberally supply the wants of a house of the largest class, and the first cost (not including piping), would not be over L4 or L5 sterling.
For town supply, the screw, pump, and gearing would require to be designed for the population; but taking for example one of the largest force pumps in the works of Messrs Burt, of this city, I find it to be 4 inches in diameter, 8 inch stroke, single action once per second. This pump in constant operation would deliver 3.5 cubic feet per minute, or 5025 cubic feet, equal to 31,155 gallons for 24 hours, which would amply suffice for the supply of a town of 1000 inhabitants. Had the water supply to be raised 100 feet above the level of the river, such as would be necessary for Balclutha, Alexandra, Clyde, or Cromwell, as one-horse power raises 5.28 cubic feet to that elevation per minute, this power, allowing amply for friction, would suffice for the above service. So, were a screw applied to the pump revolving in a current of 7 miles per hour, one of 3 feet 6 inches in diameter would do the duty.
The cost of the apparatus complete, delivering water at the top of the bank (not including street pipes, &c.) will of course vary with the nature of the posisition and relative facilities afforded. Where the river is narrow, the screw and pump would best be held by a wire cable stretched across the current or arm of the rive. Where the banks are steep and rocky, a boom secured by stays and guys would be the best mode. Where the river is wide, a small punt, or even a barrel or buoy, might be used, and so forth. In either case the cost would not vary very much, so, taking the first by way of example, the following is an approximate estimate:- [Ed. first table goes here]
In this case, for the avoidance of damage by heavy floods, arrangements would be made to elevate the wire cable and draw the screw and pump in shore till they had abated. I have already given the dimensions of a screw required to raise one sluice head (95 cubic feet per minute) 70 feet above the level of the river, and an approximate estimate of the cost of the same would be as follows. The duty required would take a single acting pump 14 inches diameter and 18 inches stroke per second, or double acting, 11 inches diameter and 14.5 inches stroke of same velocity:-[Ed. second table goes here]
Of course the cost would be much modified by position and the relative facilities given by the state of the river, its banks, rocks, and currents. In applying the large machinery, it would be advisable to choose such sites as would afford rock foundations for the pump and gearings, so as to avoid the necessity of supporting the same by cable or punt, and in such cases the permanent material (cast iron) might be used solely for the piping.
As the altitude of water to be raised in many parts, especially below the Teviot, does not require to be so great, of course much reduction in cost could also be effected. This remark is also particularly applicable to the service of pumping water from river bank claims •carried on below the level of the stream surface, where the height to be raised is generally small.
In many parts of the goldfields of Otago large capital has been expended in bringing water to claims on the banks of the Clutha now worked out. The cost of bringing in water when not available for other claims thus remains a loss. Thus a great advantage is gained under such circumstances by the introduction of the contrivance and machinery proposed, inasmuch as the plant can be removed to other localities, and re-erected for new operations.

£ s. d.
50 fathoms of 3-inch galvanised iron wire rope ... .. 8 15 0
Pump ... ... ... ... 10 0 0
Screw ... ... ... ... 10 0 0
150 feet of 2-inch indiarabber tubing at 2s 6d per foot ... 18 15 0
150 do do iron piping, at 1s 3d per foot ... ... ... 9 7 6
Carriage and labour of erecting... 50 0 0
£106 17 6

£ s. d.
Pump ... ... 65 0 0
Screw ... ... ... ... 20 0 0
50 fathoms of 4 1/2 inch galvanised iron wire 45 0 0
150 feet of leather, 6 inch hose, at 5s per foot 37 10 0
150 feet of cast iron 6 inch pipes, at 4s per foot 30 0 0
Carriage and labour (say) ... 100 0 0
297 10 0

The Dunstan Times sounded a note of caution - the idea was not particularly original, and something similar had already been tried: Dunstan Times, Issue 468, 7 April 1871

The model of a self acting water pumping machine made by Mr. J. T. Thomson, Provincial Engineer, and exhibited at the Water of Leith, Dunedin, appears to attract considerable attention. We have not seen the model ourselves, but from its description, there appears nothing to prevent the success of a similar machine on a large scale. That the enormous motive power of the Molyneux should be utilised to extract some of the mineral treasures which line its banks has long been in contemplation by observing men. We must give Mr. J. T. Thomson much credit for his valuable ideas on the subject, also Mr. Drummy who constructed something like to Mr. Thomsons apparatus yet we must not place the gentlemen in the category of invent[...] allow them the honor of havihg puth their ideas into practicable shape. Clyde may take much credit to itself for always having been foremost in developing the golden treasures of the Molyneux, and it was solely through the exertions of the people of this town that the first dredging machine was constructed. Like most originators their first effort was a failure, not that the idea was impracticable, but because the minor details were not carried out with that precision which could only be acquired as the result of experience. In the Alabama now working between this and Alexandra may be witnessed the first efforts of the people of Clyde to dredge the Molyneux for gold. She is working upon the principle of her original designers, the process of raising the gravel from the bottom of the river being exactly the same. As we said before it was only the fault of a few minor details that marred success in the very first instance. But a very short time elapsed between the failure of the dredge, and the starting of a self acting pumping machine, the invention of a Mr. Dunn, a miner, of considerable mechanical ingenuity, residing a few miles up the river from Clyde. When Dunn made his project known, funds were quickly subscribed to construct a working model, which was accordingly made, tried in the river and found to answer. It consisted of a series of movable floats, revolving with the action of the current, and which worked a couple of force pumps on a platform over the top. It was considered at the time that the machine wanted power, unscientific people foolishly imagining that the little model should throw water right up the steep banks into the town, and thus the affair fell through. Mr, M'Pherson’s punt was constructed shortly after this, and then the idea of fixing two punts together with an undershot wheel, with feathering floats, and mooring the machine in the river was mooted, but from some causes public interest in the matter flagged and nothing was done. Alexandra next took up the question of obtaining power from the Molyneux, and some screw wheels were constructed on the principle of a three bladed propeller, which were successfully used in working pumping machinery at Frenchman’s Point, Butcher’s Point and on the Manuherikia River. A considerable amount of power appeared to be obtained from these wheels, and they possessed the advantage of working when totally immersed. When placed in a rapid, they gave evidence of suppling the long felt want, but unfortunately they fared the same fate as the original contrivance. We do not of course desire to disparage either Mr. Thomson’s or Mr. Dummy’s inventions, but we like to see honor awarded where honor is due. The goldfields’ population possess very inventive ability, and were not this the case, gold-mining would not have reached its present perfect state. The enormous power running to waste in our rivers could all be applied to the raising of water for mining purposes, while it could be made available for a great variety of other uses. We have miles upon miles of auriferous terraces only lacking a water supply to afford employment to hundreds. In fact, could some cheap process of raising water from our rivers in sufficient quantity for sluicing purposes be effectively accomplished and sufficiently cheap to be within the reach of ordinary mining parties, the gain would be immense. A premium given by the Government to the first person, who by the aid of a self acting current wheel succeeds in raising sufficient water out of a river for sluicing purposes, would be money judiciously expended. This is a subject which might possibly interest the water commissioners, whose recommendation might perhaps accomplish something, which would load to a satisfactory result.

A flour mill is about to be erected at Kaihiku by Mr Doull. It is to be worked by the process described by Mr J. T. Thomson at a meeting of the Otago Institute about three months ago, and christened in the country districts "Thomson's screw."

It is reported that the screw principle of motive power designed by J. T. Thomson, Esq., and proposed to be applied to Mr Doull's flour mill on the Clutha river, has not proved effective, and that a paddle-wheel is to be substituted.

THE SCREW LOOSE!
To the Editor.
Sir, - I read a paragraph in your paper last evening, stating that the screw of Mr J. T. Thomson had been applied to a mill on the Clutha River and failed. If so, there has been some misapprehension of his "style of screw." People who understand its principle thoroughly have no hesitation in saying that, if details are carried out in accordance with his ideas, no application of the screw can be more effectual. —I am, &c., Mechanic. Dunedin, August 31.

(To the Editor of the Bruce Herald.)
Sir, - I beg to state that I am not acquainted with the style of screw adopted by Mr Doull for the Molyneux, nor its mode of application. By inserting this you will oblige. I am, &c., J. T. Thomson.