358 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL 



[October, 



fourth rate. This was done at the express command of Charles II. This 

 vessel made two voyages to the Straits, apparently for the express purpose of 

 testing the new invention, and on her return in 1G<'.'}, was careened at Uept- 

 ford, and personally inspectod by the King. An order was then issued that 

 his .NIajesty's ships should in fi!tuie he sheathed only with lead, excepting by 

 especial order from the Navy Board. It appears that about 20 ships of the 

 royal navy were consequently sheathed with milled lead, and fastened with 

 copper nails. — Even the royal protection could not save this invention from 

 cavillers, so that, in ICT" and 1078, complaints were made by Sir John Nar- 

 borough and Sir John Kempthorne, that the rudder irons of the IMymouth 

 and the Dreadnought were so much eaten, as to render it unsafe for those 

 Tessels to proceed to sea ; these complaints were repeated in 16S2. — The pa- 

 tentees maintained, on the contrary, that the damage to the rudder irons 

 could not possibly arise from their being covered with lead, as it had been 

 the invariable practice for a great many years, to secure the iron work of 

 ships, generally, by lead covering, and especially by capjiing the beads of 

 their bolts, under water, with lead, seized to and nailed over them. Reports 

 too in favour of the invention were made by Sir I'hineas Pett, and by Mr. 

 Betts, master builder, at Portsmouth, in which the latter stated, that lead had 

 effectually prevented the vessels becoming what is technically termed " iron- 

 sick," meaning that the bolt-holes became so widened by corrosion, that the 

 bolts were loosened ; he recommended, however, that the lead sheathing 

 should be stripped every seven years, on account of the decay of the oakum 

 in the joints ; declaring, too, that it became less foul on the voyage than wood 

 sheathing, and was much more easily cleaned. These different opinions led 

 I to the issue of an Order i]i Council in 1C82, for the appointment of commis- 

 sioners to examine and report upon the alleged injury to the iron work by 

 milled lead covering ; it is |)robable their report was unfavourable, as it is 

 said that the use ot lead covering, fastened with copper nails, was abandoned 

 on account of the rapid corrosion of the rudtler irons. A controversy appears 

 to have arisen on this subject, the merits of which it would be difficult to as- 

 certain after such a lapse of years. Government, however, subsequently de- 

 termined to make another trial of the value of lead covering ; accordingly, 

 the .Marlborough was so sheathed, and laid up in ordinary, at Sheerness. A 

 few years after, she was docked, at Chatham, in 1770, when it was found that 

 the lead sheathing was covered with weeds, and the iron fastenings very much 

 decayed ; the lead was in consequence removed, and a wood sheathing sub- 

 stituted. 



Mixture of metals. — Several patents were afterwards obtained for different 

 mixtures of metal for this purpose, none of which seem to have succeeded, 

 being all subject to the same inconveniences as the simple metal ; among 

 vrhich was the influence of the sun in the torrid zone, which was said to re- 

 duce the lead, in the course of five or six years, to a calx. — .\mong these 

 patents, for mixed metals for sheathing, is mentioned that of Mr. Bulteel, in 

 1693 ; it was found to have all the inconveniences of lead. Mr. Donithorue, 

 in 1780, obtained a patent for sheathing, of a mixture of 112 parts of tin to 

 10 parts of zinc; this was also as objectionable as lead. — Slade's patent for 

 sheathing with copper laid upon lead, and the patents of Wetterstedt, and of 

 Muntz, for mixed metals, are examined ; and the author promises a continua- 

 tion of the subject, with the liistory of copper sheathing. 



BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 



Eleventh Meeting, 1841. 



(From the reports of the Athenceum.J 



" On Trtmcott's plan for Reefii^ Paddle Wheels." 



Mr. Chatfield described, by reference to a model, an improved paddle- 

 wheel, the principal feature of which was a new application of the principle 

 of feathering and reefing. Each paddle or float is attached to an axis passing 

 through its centre, with a crank at the extremity of the axis, and the feather- 

 ing is elfected by the motion of a roller attached to this crank, and moving 

 in a groove eccentric to the wheels. The radii of the paddle wheel are con- 

 nected at their extremities by a chain instead of a rigid rim, and the reefing 

 is effected by drawing the radii together, like the folding of a fan. by means 

 of a peculiar arrangement of the clutch box at the centre of the wheel. 



" On a Plan of Disenyaging and Reconnecting the Paddle WheeU of Steam 

 Engines. By J. Grantham. 



There are four cases in which it may he desirable to disconnect the paddle 

 wheels from the steam engine in steam vessels, viz., when the vessel is on a 

 long voyage, and the fuel must be economized as much as possible by using 

 the sails on every favourable opportunity ; when the engines are damaged, 

 and, the vessel being close to a lee shore, it is necessary to disengage the en- 

 gines quickly, to allow the vessel to make sail ; when some derangement has 

 taken place, and the engines are allowed to continue to work imperfectly to 

 the end of the voyage, rather than detain the vessel by causing the paddles 

 to drag throngh the water while the engines are stopped ; when, the vessel 

 being at anchor, the action of the swell and tide on the paddle floats, while 

 stationary, causes a great additional strain on the cables, which would he ob- 

 viated could the wheels play freely. The Admiralty had called attention to 

 the subject, by inviting ])lans for effecting it. Several had been proposed for 

 disconnecting the paddles, but Mr. Grantham is not aware of any plan hav- 



ing been proposed by which the wheels could be readily reconnected in a 

 heavy sea. The crank pins are usually fixed in the cranks of the intermediate 

 shaft, a little play being allowed in the eye of the crank of the paddle shaft, 

 to prevent the crank pins from breaking when the centres of the three shafts 

 vary from a straight line by the yielding of the vessel. For the purpose of 

 disengaging and reconnecting, a brass box of a rectangular form is inserted 

 in the eye of the crank of the paddle shaft, which can be moved several inches 

 by means of a screw at the back of the crank. The eye of the crank is so 

 made that two of its sides may be cut away, and through these openings the 

 crank pin can pass when the box is drawn back, or the disengaging effected. 

 The brass box has one of its side.s which restrain the crank pin when in gear, 

 cut away one or two inches to assist in reconnecting the engine, which it 

 eflecfed by screwing the box out one or two inches, or just so far that the 

 crank pin can pass the side which has been cut away, and come in contact 

 with the higher side. This is the correct position for reconnecting, which is 

 accomplished by a single turn of the screw. 



Mr. Grantham, in reply to a question from Capt. Taylor, R.N., stated tliat 

 he should consider it very dangerous to disconnect the paddle wheels \rithoat 

 having first stopped the engine. 



" On the Projjukicn of Vessels by the Trapezium Paddle-wheel and Screw." 



Mr. G. Rennie gave an account of the various experiments to which he had 

 been led, on the propulsion of vessels by various forms of paddle floats and 

 by the screw. It was generally admitted that the i)addle wheel was the best 

 means of propulsion with which engineers were at present acquainted, and 

 various attempts had been made for its improvement. There are several ob- 

 jections to the square or rectangular floats, particularly the shock on entering 

 the water, and the drag against the motion of the wheel on the float quitting 

 the water ; both of which give rise to considerable ribrations. He had been 

 led, in considering the improvement of the paddle wheel, to have recourse to 

 nature ; and the form of the foot of the duck had particularly attracted his 

 attention. The web of the duck's foot is shaped so that each part has a re- 

 lation to the space through which it has to move, that is, to the distance 

 from the centre of motion of the animal's leg. Hence he was led to cut off 

 the angles of the rectangular floats, and he found that the resistance to the 

 wheel through the water was not diminished. Pursuing these observations 

 and experiments, he was led to adopt a float of a trapezium or diamond shape, 

 with its most pointed end downwards. These floats enter the water with 

 their points downwards, and quit it with their points upwards, and then arrive 

 gradually at tlieir full horizontal action, without shocks or vibrations ; and 

 after their full horizontal action, quit the water without lifting it, or produc- 

 ing any sensible commotion behind. After a great variety of experiments, he 

 found that a paddle wheel of one half the width and weight, and with trape- 

 zium floats, was as eflective in propelling a vessel as a wheel of double the 

 width and weight with the ordinary rectangular floats. The .-Vdmiralty had 

 permitted him to fit Her Majesty's steam ship African with these wheels, and 

 he had perfect confidence in the success of the experiment. Another means 

 of propulsion was the screw, which had been applied with success by Mr. 

 Smith in the Archimedes. In examining the wings of birds and the tails of 

 swift fish, he had been particularly struck with the adaptation of shape to the 

 speed of the animals. The contrast between the shape of the tail of the cod- 

 fish, a slow moving fish, and the tail of the mackerel, a rapid fish, was very 

 remarkable,— the latter going off much more rapidly to a point than the 

 former. From these observations he was led to try a screw with four wings, 

 of a shape somewhat similar to these, but bent into a conical surface, the 

 outline being a logarithmic spiral. He found also that certain portions of 

 these might be cut off without diminishing the effect. With respect to as- 

 certaining the friction of the screw on the water, great difBculty existed ; hut 

 he would refer to his experiments, published some years ago in the Philoso- 

 phical Transactions, in which he measured the friction of the water against a 

 body revolving in it, by the time which a given weight took to descend ; this 

 body consisted of rings, and he found that the friction or resistance throagh 

 the water did not increase in proportion to the number of rings. 



" On a Floating Breakwater." Dy Capt. Taylor, R.N. 



The breakwaters hitherto constructed have generally consisted of solid 

 masonry, thus presenting an unyielding obstacle to the waves, and permitting 

 accumulations of mud and sand behind them, and not aftbrding the security 

 to shipping and life which is required, and may be afforded by other means. 

 The floating breakwater consists of floating sections framed of timber, moored 

 to piles ; these sections yield to the shocks of the sea, and admit the wave to 

 pass under, over, and through them, and by thus dividing the waves, reduce 

 them to an open and harmless state. The forms of these sections vary ac- 

 cording to the situations in which they are employed. The sea in the most 

 tempestuous weather is said to be tranquil at the depth of sixteen or eighteen 

 feet below the surface ; a l)reakwater, therefore, immerged to that depth, and 

 presenting six or eight feet above the surface, is sufficient to form a safe har- 

 bour on the most boisterous coast. The angle of inclination which the sec- 

 tion presents to the wave is that pointed out by nature in the Mew-stone, 

 viz. 35 degrees. Stone breakwaters check the ground tides, and cause accu- 

 mulations of mud and deposits which otherwise would go seaward, and are 

 pecuUarly subject to the action of the teredo, constantly at work below the 

 doTC-tailed stone; and cavities being formed, large portions are occasionally 

 blown up. The destruction by the teredo may be obviated or arrested in the 

 floating breakwater by tarring the wood with a preservative mixture, or by 

 restoring from time to time such portions as are injured. The distinction 



