Life of Richard Trevithick by F. Trevithick: Volume 1: Chapter 11
CHAPTER XI. HIGH-PRESSURE STEAM-DREDGER
The late Mrs. Trevithick said that her husband was good-tempered, and never gave trouble in home affairs, satisfied with the most simple bed and board, and always busy with practical designs and experiments from early morning until bed-time. He sometimes gossiped with his family on the immense advantages to spring from his high-pressure steam-engines, and the riches and honours that, would be heaped on him and his children, but thought little or nothing of his wife's intimations that she barely had the means of providing the daily necessaries of life.
Captain John Vivian, at the period of steering the London common road locomotive in 1803, "saw Trevithick breaking the rock at the East India Dock entrance to the Thames at Blackwall using a water-wheel worked by the tide, and also a small high-pressure engine for driving or turning large chisels and borers, and other contrivances for breaking and clearing away the rock to increase the depth of water.".
A little more than thirty year ago, the writer lodged in the house of a Mr. and Mrs. Bendy, at Slough, who took an especial interest in his comfort, because he was the son of the inventor of the steam-dredger and the locomotive. Mr. Bendy had worked on the first steam-dredger, and thought that Mr. Trevithick was unkindly and unfairly treated, for the machinery was complicated, and when anything had gone wrong he perhaps spoke sharply to those about him. The ballast-men on the Thames did everything they could to prevent the use of the steam-dredger and there were other more secret enemies, who offered Mr. Bendy a bribe to so fix the particular work in his charge as to cause a breakage.
Things went very well for several days after the first putting to work of the steam-engine dredger, and then there was a breakage, caused by a nut jammed in the cog-wheels: many believed it was purposely done.
The following letter was written twelve years after those conversations:—
Nov. 8th, 1840.
DEAR MR. TREVITHICK,
I will furnish you with all the particulars I recollect respecting the dredger-engine and machinery made by your father for Mr. Bough. It was fixed in the year 1803, and was altered by Mr. Deverill (the patentee of the double engine) in the year 1805. The cylinder was 14.5 inches in diameter, the stroke 4 feet, the chain-ladder 28 or 30 feet. The largest quantity of stone and gravel lifted in one tide was 180 tons. The reason for using the word stone is from its being part of Blackwell rock. The engine was cast at Hazeldine's at Bridgenorth, but finished at Mr. Rowley's factory in London, by some men from Cornwall, and a part of the machinery by Jackson, a Scotch millwright. The working time between tides was from six to eight hours, in from 14 to 18 feet of water, at the entrance of the East India Dock. The expense of the engine and machinery, a little more than £2,000. I should think the time she worked was about ten or eleven years.
The other engine you mentioned was the property of the Trinity Company and Government, but by whom made I cannot ascertain. It was worked in the river, near Woolwich entrance dock-gates, but not to much account, only lifting mud to clear the entrance. No new materials were taken there by Mr. Deverill; all that was done was to refix the old, and repair the engine. This engine was the same size as that fixed in London to run round the circle, at the speed of fourteen or fifteen miles per hour, commonly called locomotive engine.
Trevithick having seen his engine boring and dredging on the Thames in 1803, went to Wales to superintend the tramroad-engine of 1804, then to Newcastle-on-Tyne with the railroad-engine, and in the early part of 1805 he was again with the steam-dredger and rock breaking at Blackwall.
Mr. Bendy says 180 tons of stone and gravel from the Blackwall rock were raised in a tide of six or eight hours, from a depth of 14 or 18 feet. This rock breaking and dredging in deep water was a severe test for a new invention; and the Trinity Board, seeing its usefulness, engaged with Trevithick to erect and work steam-dredgers in other parts of the river.
In February, 1806, he was about entering into an engagement for twenty-one years with the Trinity Board to lift ballast from the bottom of the Thames, at the rate of 500,000 tons a year, for a payment of sixpence a ton. Dredging had been done by hand for about eight pence a ton but the required quantity could not be raised by men working small dredge-bags attached to long poles.
In May, 1806, his partner in the patent wrote: "I am very happy to find that you have so far continued your agreement with the Trinity gents. I think the bargain is a good one; must still beg leave to remind you not to proceed to show what your engine will do, till the agreement is fully drawn up and regularly signed."
In July, 1806, Trevithick wrote: — "This day I set the engine to work on board the ‘Blazer,' gun-brig. It does its work exceedingly well. We are yet in dock, and lift up mud only. I hope to be down at Barking shaft in a few days, at our proposed station, when I will write to you again. I think there is no doubt of success." An account-book in Trevithick's writing, headed "Expenses on the ballast machine from 1805 to 1807," shows that those ballast-dredging engines, like the earlier dredging engine at the Blackwell rock, came from the Bridgenorth Foundry, and many of the mechanics erecting it came from Cornwall. One of the engines was fixed in the 'Blazer,' the other in the ‘Plymouth Barge.'
Watt honoured Trevithick with a visit to inspect the steam-dredgers, having been introduced by Mr. John Rennie, of whom Smiles wrote: —
What is called the Humber Dock was begun in 1803 and finished in 1809. It was in the course of executing the Hull Harbour Docks that Mr. Rennie invented the dredging machine as it is now used. Mr. Rennie carefully investigated all that had previously been attempted in this direction, and then proceeded to plan and construct a complete dredging machine, with improved cast-iron machinery, to which he yoked the power of the steam-engine. 
Rennie's investigation prior to invention probably refers to what he saw Trevithick doing, whose dredger is unmistakably described and delineated by Rees, though the inventor's name is omitted.
The convicts at Woolwich upon the Thames perform the ballast heaving, or dredging, which they are condemned to labour at as a punishment: the above method of manual labour became so expensive, that a large machine, worked by horses or a steam-engine, is usually employed. Two such machines have been some time in use in the river Thames. It is erected in the hulk of a dismasted ship.
Plate VIII.:- A A, Fig. 1, is a frame of timber bolted to the starboard gunwale, to support a large horizontal beam, B B, Fig. 2 another similar frame is fixed up in the middle of the ship at D, Fig. 2, and the end of the beam is sustained by an upright post bolted to the opposite. gunwale; the starboard end of the beam projects over the vessel's side, and has an iron bracket, S, fastened to it, to support one of the bearings for the long frame, E E, composed of four timbers bolted together the other end of the frame is suspended by pulleys, a a; from a beam, F, fixed across the stern, the upper ends of the outside beams of the frame, E E, have each a stout iron bolted to them, which are perforated with two large holes to receive two short cast-iron tubes; one fastened to the iron bracket, S, at the end of the beam, B, and the other to a cross beam of the frame, A. These tubes act on the pivots of the frame, E, upon which it can be raised or lowered by the pulleys, a a they also contain bearings, for an iron axis, on which a wheel or trundle, 0, is fixed, containing four rounds. Another similar trundle, P, is placed at the bottom of the frame E E; and two endless chains, k k, pass round both, as is seen in the plan. Between every other link of the two chains, a bucket of plate-iron, b b b, is fastened, and as the chain runs round, the buckets bring up the soil a number of cast-iron rollers, d d, are placed between the beams of the frame to support the chain and buckets as they roll up. Four rollers, e e, are also placed on each of the outside beams, to keep the chains in their places on the frame, that they may not get off to one side. The motion is conveyed to the chains by means of a cast-iron wheel at G in the plan, wedged on the end of the axis of the upper trundle, 0. The wheel is cast hollow, like a very short cylinder, and has several screws tapped through its rim, pointing to the centre, and pressing upon the circumference of another wheel enclosed within the hollow of the first, that it may slip round in the other when any power greater than the friction of the screw is applied; the internal wheel is wedged on the same shaft with a large cog-wheel, f, turned by the small cog-wheel, g, on the axis of the steam-engine.
The steam-engine is one of that kind called high pressure, working by the expansive force of the steam only, without condensation. b is the boiler containing the fire-place and cylinder within it; i is one of the connecting rods; and l the fly-wheel on the other end of the same shaft as the wheel g.
The pulleys, a, which suspend the chain-frame are reeved with an iron chain, the tackle-fall of which passes down through the ship's deck, and is coiled on a roller, as in the plan, and represented by a circle in the elevation; on the end of the roller is a cog-wheel, p, turned by the engine-wheel, g; the bearing of this wheel is fixed upon a lever, one end of which comes near that part of the steam-engine where the cock which regulates the velocity of the engine is placed; so that one man can command both lever and cock, and by depressing that end of the lever, cause the wheel p to gear with g, and, consequently, be turned thereby, and wind up the chain of the pulleys; g is a strong curved iron bar bolted to the vessel's side and gunwale, passing through an eye bolted to the frame, E, to keep the frame to the vessel's side, that the tide or other accident may not carry it away.
A large hopper or trough is suspended beneath the wheel, o, by ropes from the beam, B, into which the buckets, b b b, empty the ballast they bring from the bottom; the hopper conveys it into a barge brought beneath it. This hopper is not shown, as it would tend to confuse parts already not very distinct. The motion of the whole machine is regulated by one man.
The vessel being moored fast, the engine is started, and turns the chain of buckets; the engine tender now puts his foot upon a lever, disengages the wheel p from g and by another takes off a gripe which embraced the roller m. This allows the end, E, of the frame to descend, until the buckets on the lower half of the chain drag on the ground, as shown in Fig. 1, when he stops the further descent by the gripe. The buckets are filled in succession at the lower end of the frame, and brought up to the top, where they deliver their contents into the hopper before mentioned; as they take away the ballast from the bottom, the engine tender lets the frame E down lower by means of the gripe-lever, and keeps it at such a height that the buckets come up nearly full. If at any time the buckets get such deep hold as to endanger the breaking of the chain or stopping the engine, the coupling box at C, before described, suffers the steam-engine to turn without moving the chain of buckets, and the engine tender pressing his foot upon the lever which brings the wheel p to gear with g, causes the roller n to be turned by the engine, and raise up the frame E, until the buckets take into the ground the proper depth, that the friction of the coupling box at C will turn the chain without slipping in any considerable degree.
The steam-engine is of six horses' power, and is so expeditious that it loads a small barge with ballast in an hour and a half."
Trevithick's expeditious steam-dredging engine was “of that kind called high pressure, working by the expansive force of the steam only, without condensation," very like Mr. Wilson's description of the Newcastle locomotive engine, for in principle if not in outline the two engines were alike.
If Rennie commenced his dock operations in 1803 Trevithick was then breaking and clearing the rock from the dock entrance to the Thames at Blackwall, when Captain John Vivian gave his spare days to ride on the London common road locomotive, and to the works at the dredger. In 1805, while the dredger was still going on, Rennie's report to the directors of the Thames Driftway was put aside, and Trevithick was appointed as the engineer; in 1806 the dredgers were in full operation, or the Trinity Board would not have proposed a contract for a term of years; and in 1807 he was still in daily attendance on the dredging schemes: thus for several years, during the most inventive and active period of his life, did he give his time to the perfecting the steam-dredger.
This machine is memorable as the first steam-dredger, and also as leading to the locomotive of 1808 and, like many other of Trevithick's practical inventions, was near perfection at birth. Hundreds of steam-dredgers are now at work throughout the civilized world, and although their construction has occupied the time and knowledge of numerous practical engineers during a period of more than sixty years, yet this first production is the type of them all.
The small and compact high-pressure steam-puffer engine was placed in a wooden house; a main shaft extending over the side of the boat gave motion to an endless chain of dredging buckets kept in the required position by a long wooden frame, having a roller or guide-wheel at its lower end, round which the revolving chain of buckets passed, and this end of the frame was raised or lowered at will causing the lower sweep of the chain of buckets to press with greater or less weight into the bed of the river and thus cause the buckets to raise a greater or less quantity of mud or gravel. The chain and loaded buckets in going up the incline formed by the wood frame passed over rollers in order to lessen the friction on passing the top of the incline the buckets turned short round over a guide-wheel, similar to that at the bottom of the frame, with their bottoms upwards, causing their contents to fall into a barge or guide launder as was most convenient for the disposal of the ballast. The wheel giving motion to the bucket-chain was not wedged fast to the driving axle, but was bored to fit loosely on the turned part of the axle, or rather on a turned cylinder fixed firmly on the driving axle. Tightening screws in the bucket-wheel with their inner ends pressing on the cylindrical driving axle formed a friction band, and should the buckets have come in contact with an unusual obstruction, allowed the driving axle to revolve while the obstructed bucket-wheel remained stationary.
Another safeguard was provided by the rope from the block, supporting the lower end of the bucket-frame being connected with the engine, enabling the engine man without moving from his station at the engine to raise or lower the bucket-frame by putting his foot on a lever. "The steam-engine was one of that kind called high pressure, working by the expansive force of the steam only." "It is of six horses' power, and is so expeditious that it loads a small barge with ballast in an hour and a half." The steam-engine and dredging machine were so admirably arranged that "one man can command both lever and cock for regulating either the machine or the steam-engine." The feed-pump was worked with a lever, giving a shorter stroke to the feed-pole. The position of the - engine is seen in the drawing of the dredger boat; the detail of the engine is in chap. ix., that it may illustrate the progress of locomotion, for similar engines served both purposes.
A letter by Trevithick, years after the event, corroborates the work done by those dredgers.
4th February, 1813.
I have your favour of the 2nd inst. respecting an engine for lifting mud from the bottom of Falmouth Harbour.
I made three engines with machinery for lifting mud at the entrance of the East and West India Docks, and also for deepening the water at the men-of-war's mooring ground at Woolwich. One of these engines was a 20-horse power, erected on an old bomb-ship of about 300 tons burthen, which machine cost (exclusive of the ship) about £1,600.
This engine would lift and put into barges near 100 tons of mud per hour. Another engine of 10-horse power I erected on board an old gun-brig of about 120 tons burthen, which cost (exclusive of the vessel) about £1,000, which lifted about half the quantity of the large one; and another engine of 10-horse power I erected on board a barge of about 80 tons burthen.
Unless the mud will pay for bringing on shore for manure, I should think that a better plan than this might be adopted to clean the harbour.
I remain, Sir,
Your very humble servant,
(Gould, Jun., Esq., Penryn)
The first steam-dredger at Blackwall succeeded, or two others would not have been constructed. One dredger with the 20-horse-power engine lifted and placed in barges near 100 tons of mud per hour, making good his promise as to quantity. Others were used to deepen the entrance to the East and West India Docks, and also at the man-of-war's mooring ground at Woolwich, in such deep water as fully proved the correctness of their design. The three engines and dredgers, exclusive of the vessels, cost £3,600, a less sum than such machines would now be made for.
- See Trevithick's letter, May 2nd, 1803, chap. ix.
- Statement by Captain John Vivian in 1869 residing at Hayle.
- See Andrew Vivian's letter, 22nd May, 1805, chap. x.
- See Trevithick's letter, February 18th, 1806, chap. xviii.
- See Trevithick's letter, March 4th, 1806, chap. xviii.
- See Vivian's letter, May 30th, 1806, chap. xviii.
- See Trevithick's letter, July 23rd, 1806, chap. xv.
- Lives of the Engineers, by Smiles, vol. ii.
- Rees' Cyclopedia, published 1819.
- See Vivian's letter, May 22nd, chap. x
- Report of directors of the Thames Driftway, June 1805, chap. xii.
- See Trevithick's letter, August 11th, 1807, chap. xii.