25 



PONTOON. 



PONTOON. 



626 



were strained by capstans and made fast to some heavy guns which 

 were laid behind the retaining walls on the sides of the river, and 

 these ropes carried the planks which formed the roadway ; but after a 

 few weeks they were removed, and replaced by timbers, which from 

 their steadiness were found preferable. The breadth of the river 

 at the place where the bridge was formed is 810 feet, and booms were 

 moored across, both above and below the bridge, for its protection. 



The precise period at which pontoons, or flat-bottomed vessels, were 

 first employed to support a bridge is unknown. Folard observes, in 

 his observations on the fifth book of Polybius, that for passing rivers 

 the Germans in his time used vessels formed of timber frames covered 

 with leather : he adds that the Dutch troops had pontoons of wood 

 covered with tin, and that the French took some of them at the battle 

 of Fleurus, which was gained, in 1698, by the Mare'chal de Luxem- 

 bourg over the Prince of Waldeck. Mention is frequently made of 

 pontoon-bridges, both in Germany and Italy, in the beginning of the 

 18th century, particularly during the campaigns of Marlborough ; and, 

 from the speed with which they are said to have been executed when 

 required, it is probable that a corps of men was then particularly 

 employed in that branch of service. 



The pontoons employed during the war against Napoleon I. differed 

 but little from those mentioned above. They were of metal over a 

 light framework of wood tinned inside ; they were from 17 to 21 feet 

 long, from 4 to 5 feet broad, and from 2 feet to 2 feet 3 inches deep. 

 In the formation of the bridge, a rope was tightly stretched across the 

 river ; the vessels were then rowed to then* places, and each was made 

 fast at one end to the rope ; another rope was then stretched across 

 the river, parallel to the former, at the opposite ends of the pontoons, 

 and to this rope those ends were made fast. When a strong current 

 set obliquely across the river, the sides of every two pontoons were 

 sometimes connected together by rope braces stretched diagonally 

 across the intervals, in order that the effect of the current upon each 

 might be counteracted by a like effect on the next ; and in very rapid 

 streams anchors were also thrown out from each or from every second 

 or third pontoon, according to circumstances. 



Timber-baulks, or joists, were then laid from the shore to the first 

 pontoon, from that to the next, and so on, at intervals from each other 

 depending upon the breadth of the bridge or the weight to be sup- 

 ported. Every two in the direction of the length were attached 

 together by a bolt, which allowed the bridge to yield to the rise or fall 

 of the water. Above these timbers were placed the chesses, or 

 flooring-planks, close together and perpendicular to the length of the 

 bridge ; and these were kept down by a riband or a plank, which was 

 fastened over their extremities on each side of the bridge. 



General Sir Charles (then Colonel) Pasley, to whom the department 

 of military engineering in the British service is so much indebted for 

 the improvements which he has introduced into every branch of art 

 connected with practical fortification and siege operations, has proposed 

 a description of pontoon. The form of the old pontoons rendering them 

 difficult to manage in the water, and their great weight, when it was 

 necessary to transport them from place to place by land, causing them 

 to be a serious encumbrance to an army on its march, that officer was 

 led to construct the pontoons in the form of canoes, with decks, each 

 end being shaped like the head of a boat, in order that they might be 

 easily moved through the water by rowing, with either end foremost. 

 They are constructed of light timber frames, covered, except the deck, 

 with sheet copper ; and each vessel ia formed in two equal parts by 

 transverse partitions, so that the demi-pontoons may be separated 

 from each other when the bridge is to be conveyed on carriages by laud 

 with the army. When in the water, the parts are connected together 

 by a rope, which passes through two perforations in the keel, near the 

 place of junction, and by a rectangular frame of wood, which is laid 

 along the deck, and attached to it by lashings. Each half- vessel is also 

 divided into two compartments by a partition ; and small pumps are 

 provided, by which the pontoon may for a time be kept afloat, should a 

 hole be made in its side by a shot or by any other accident. 



Sir James Colleton, some years since, invented pontoons of wood of 

 a cylindrical form, some o hvhich have been occasionally employed in 

 experimental operations ; and cylindrical pontoons of tin, which were 

 subsequently invented by the late General Blanchard, were introduced 

 into the service. Then List have hemispherical ends, and are divided 

 both longitudinally and transversely into several compartments by 

 partitions of tin, both to increase their strength and to prevent them 

 from sinking in the water in the event of their being accidentally per- 

 forated in any part. They possess the advantages of great lightness 

 and buoyancy ; but they have not the durability of copper vessels, and 

 they must be very liable to be injured when transported by lartd, 

 particularly if a march should take place under a hot sun. 



In 1836 the comparative merit* of General Pasley's and General 

 Blanchard's pontoons were tried upon the Medway, when large bodies 

 of infantry and cavalry, besides three pieces of artillery, were made to 

 pass over the river on bridges supported by vessels of the two kinds. 

 The order of march was purposely such as to subject the bridges to 

 the severest strains ; and a superiority of steadiness on this occasion 

 appears to have led to a preference in favour of the pontoons proposed 

 by the last-mentioned officer. 



The breadth and depth of one of General Pasley's pontoons are 

 2ft. Sin. The diameter of one of General Blanchard's cylin 



ARTS AHD SCI. DIV. VOL. VF. 



2 ft. Sin. The length of the former kind of pontoons is 22 ft. ; of the 

 latter, 24 ft. 6 in. 



The manner of forming the bridge, with both kinds, is nearly the 

 same. A rectangular frame, whose length is about equal to the breadth 

 of the platform for the intended bridge (12 feet), is laid down longi- 

 tudinally on the deck of the canoe, or on the surface of the cylinder, 

 and is kept in its place by rope-lashings ; on the upper surface' of this 

 frame, in the direction of its breadth, are nailed pieces of wood in 

 pairs, at equal intervals ; the distance between every two in each pair 

 being little more than equal to the breadth of a baulk, or joist 

 (2^ inches), one extremity of which is to be received between them, 

 and the number of pairs being equal to the number of baulks which 

 are to support the chesses or planks forming the roadway. A raft is 

 formed with two of these pontoons, by placing them parallel to each 

 other, at a distance, from centre to centre, equal to about 12 4 feet; 

 the ends of two baulks, or transoms, as they are called, are made to 

 rest upon the frames before mentioned, the distance between them 

 being equal to the intended breadth of the bridge, and they are kept 

 steady by having near each extremity a hole bored through them, into 

 which enters an iron pin fixed vertically for the purpose in the frame : 

 they are also made fast to the pontoons by ropes passing through rings 

 on the decks. Three or more baulks are then laid down parallel to the 

 transoms, with their extremities confined between the cross pieces 

 nailed to the frames as above said : the chesses are laid close together 

 above them, and thir ends are kept down by ribands, which arc 

 attached to the transoms by lashings passing over them, and under the 

 latter, at intervals. In those ribands are fixed rowlock pins ; and when 

 the bridge is not formed, the ribands being then placed parallel to the 

 lengths of the pontoons, at the sides of the raft, the latter may be 

 moved on the water by the oars. 



When the bridge is to be formed, a certain number of such rafts are 

 rowed to their stations in a line across the river, the lengths of the 

 pontoons being parallel to the banks, and there anchored ; the distances 

 between the nearest pontoons in two rafts being equal to that between 

 the two pontoons in each raft. Then each raft carrying the materials 

 which are to make a platform over the water between itself and the 

 next, such platform is laid down in a manner similar to that which is 

 employed in laying down the platform of the raft ; and from each of the 

 extreme pontoons a like platform is extended to the shore of the river. 



When the banks are favourable, the complement of men attached to 

 each raft of two pontoons -namely, one non-commissioned officer and 

 six privates can dismount two vessels and their stores from the 

 carriages, launch them, and form the raft in a quarter of an hour. All* 

 the rafts being put together at the same time, the whole bridge may 

 be formed in another quarter of an hour. After the passage has been 

 effected, the bridge can be dismantled in eight minutes ; the rafts can 

 then be taken to pieces, and the vessels and stores re-packed on the 

 carriages in a quarter of an hour. 



In order to convey the pontoons with an army, each is placed, with 

 all its accompaniments, on a four-wheeled carriage. General Pasley 

 proposes to use only a cart with two wheels for each pontoon, the 

 latter being separated into two demi-pontoons, which are placed side 

 by side above their stores. The shortness of these carriages enables 

 them to be turned within a smaller space than would be required for a 

 four-wheeled waggon ; but the weight on the shaft-horse in hilly 

 countries would be so great that it would be hardly practicable. 



The inconvenience attending the transport of pontoons, or the 

 necessity of passing a river when they are not at hand, has induced 

 commanders of armies to have recourse to bridges supported on rafts 

 of timber or on empty casks, which in Europe can always be procured. 

 Each raft may consist of four or more rough trunks of trees lashed 

 together, and may be retained in its place by anchors, or by being 

 made fast to a rope stretched across the river : the baulks and chesses 

 are applied as in a pontoon bridge. Perhaps the greatest raft-bridge 

 ever formed is that which was executed by General Sokolniki over the 

 Niemen at Grodno, in 1792. Trunks of trees from 50 to 60 feet long, 

 and from 20 to 28 inches in diameter, were united by tens, and every 

 ten were bound together at both ends by transverse braces, so as to 

 form a raft, which, as all the large ends of the trees were placed con- 

 tiguo\isly, resembled the voussoir of a bridge. All the voussoirs, 57 in 

 number, were placed in the river, side by side, in an arc of a circle 

 having its convexity towards the upper part of the river ; and a sort of 

 key- voussoir was formed by a vessel 116 feet long and 22 feet wide, 

 which was moored in the river where the current was the most rapid. 

 Baulks and planks were placed, an usual, above the rafts to form the 

 road. The breadth of the river at that place is about 1080 feet. 

 (Berard, ' Equilibre des Voutes.') 



A strong raft-bridge was formed by the Russians and Prussians over 

 the Elbe, near Dresden, in 1813 : one course of logs disposed parallel- 

 i wise to each other formed the bottom of each raft ; cross-timbers were 

 laid above these ; and over them was a third course of timbers, each 

 ' placed above the interval between two of those below it. The timbers 

 were well lashed together; a strong cable was stretched across the 

 river on each side of the bridge, which was further retained in its 

 place by anchors, and a road was formed of planks as usual. While 

 the British army was serving in Spain during the Peninsular war, the 

 roofs of buildings were occasionally t:iken to form rafts : the rafters 

 served as baulks ; and, for want of nails, the planks were kept clown 



8 s 



