Page:EB1911 - Volume 22.djvu/82

Continental armies had meanwhile constantly adhered. Captain Fowke, R.E, invented a folding open bateau, made of waterproof canvas attached to sliding ribs, so that for transport it could be collapsed like the bellows of an accordion and for use could be extended by a pair of stretchers. This was followed by the pontoon designed by Colonel Blood, R.E., an open bateau with decked ends and sides partly decked where the rowlock blocks were fixed. It consisted of six sets of framed ribs connected by a deep kelson, two side streaks, and three bottom streaks. The sides and bottom were of thin yellow pine with canvas secured to both surfaces by india-rubber solution, and coated outside with marine glue. The central interval between the pontoons in forming a bridge was invariably maintained at 15 ft.; for the support of the roadway five baulks were ordinarily employed, but nine for the passage of siege artillery and the heaviest loads; they fitted on to saddles resting on central saddle beams. The pontoons were not immersed to within 1 ft. of the tops of their “coamings” when carrying ordinary loads, as of infantry in marching order “in fours” crowded at a check, or the 16-pounder R.M.L. gun of position weighing 43 cwt.; nor were they immersed to within 6 in. when carrying extraordinary loads, such as disorganized infantry, or the 64-pounder R.M.L. gun weighing 98 cwt. In designing this pontoon the chief points attended to were—(1) improvement in power of support, (2) simplification in bridge construction, (3) reduction of weight in transport, and (4) adaptation for use singly as boats for ferrying purposes. One pontoon with the superstructure for a single bay constituted a load for one: waggon, with a total weight behind horses of about 40 cwt.

The following table (from Ency. Brit. 9th ed.) shows the powers of various pontoons in use by different nations in the past. Modern improvements are comparatively few. The “working power of support” has been calculated in most instances by deducting from the “available buoyancy” one-fourth for open and one-tenth for closed vessels:—

Pontoon.	Length.	Displace-  ment of Pontoon.	Actual Buoyancy of Pontoon.	Weight of pontoon and one bay of Super- structure.	Available Buoyancy.	Working Power of  Support.	Central Interval in Bridge.	Power per lineal foot  of Roadway.	Greatest ordinary Load per foot lineal.	Width of Roadway.	Greatest possible load at 100 ℔ per  foot superficial  of roadway.
	Ft.	Cub. Ft.	℔	℔	℔	℔	Ft.	℔	℔	Ft.	℔
Gribeauval: open bateau, oak	36·3	593	45,044	8,044	37,000	27,750	22·8	1,215	840	15·6	35,568
Austrian: open, wooden, 1799	27·0	354	22,123	3,332	18,791	14,093	16·6	849	560	11.4	18,924
Aust.-Birago: open, wooden; two pieces	28·0	303	18,907	3,249	15,658	11,744	21·7	542	560	9·3	20,181
„   „   „three „	39·4	445	27,791	3,884	23,907	17,930	21·7	827	560	9·3	20,181
„   „   iron; two pieces	28·0	353	22,090	3,698	18,392	13,794	21·7	636	560	9·3	20,181
„   „  „   three „	39·4	530	33,135	4,501	28,634	21,476	21·7	991	560	9·3	20,181
French: open, wooden; reserve	30·9	325	20,286	3,608	16,678	12,509	19·7	635	560	10·5	20,685
„   „  „ advanced guard	19·7	156	9,734	1,506	8,228	6,171	16·4	376	560	9·3	15,252
„   „  „ general	30·9	321	20,065	3,153	16,912	12,684	19·7	644	560	9·8	19,306
Prussian: open, wooden; open order	23·7	164	10,226	2,393	7,833	5,875	15·3	384	560	9·9	15,147
„   „  „   close order	23·7	164	10,226	2,213	8,013	6,010	11·2	535	560	9·9	11,088
„   „  iron; open order	24·7	214	13,385	2,209	11,176	8,382	15·3	561	560	9·9	15,147
„   „  „  close order	24·7	214	13,385	2,029	11,356	8,517	11·2	759	560	9·9	11,088
Italian: open wooden; one piece.	19·6	283	17,660	3,582	14,078	10,559	26·3	402	560	9·8	25,774
„  „   „    two pieces	39·2	565	35,320	4,572	30,748	23,061	26·3	878	560	9·8	25,774
„   modified; one piece	24·6	325	20,290	3401	16,889	12,669	23·0	551	560	9·8	22,540
„   „    two pieces	49·2	649	40,580	4,489	36,091	27,068	23·0	1,178	560	9·8	22,540
Russian ${\Big \{}$ open, canvas on wooden framework; ${\Big \}}$ open order close order	21·0	209	13,042	2,355	10,687	8,015	16·6	493	560	10·4	17,264
	21·0	209	13,042	2,083	10,959	8,219	11·7	705	560	10·4	12,168
Belgian: open, iron; one piece	24·8	297	18,584	3,336	15,248	11,436	19·7	580	560	9·5	18,715
„   „  „    two pieces	49·2	595	37,168	4,548	32,620	24,465	19·7	1,244	560	9·5	18,715
American ${\Big \{}$ india-rubber,  three; cylinders connected; ${\Big \}}$ open order close order	20·0	130	8,125	1,980	6,145	5,530	18·0	307	580	11·0	19,800
	20·0	130	8,125	1,824	6,301	5,761	14·7	393	560	11·0	18,370
English Pontoons.
Peninsular  equipment ${\Big \{}$ open, tin; reserve   „  „   advanced guard	18·9	209	13,092	2,374	10,718	8,039	16·8	477	560	10·0	16,800
	15·1	120	7,520	1,654	5,866	4,400	14·0	314	560	9·0	12,600
Pasley: closed demi-canoe; copper	25·0	141	8,781	2,103	6,678	6,010	12·5	481	560	10·0	12,500
Blanshard: cylinder, tin; open order	22·5	109	6,785	1,600	5,185	4,667	12·5	373	560	10·0	12,500
„   „  „   close order	22·5	109	6,785	1,408	5,377	4,839	8·3	581	560	10·0	8,300
„   „  „   light pattern	15·5	26	1,640	340	1,300	1,170	5·3	220	280	7·0	3,710
Fowke: open, collapsible, canvas; open order	22·0	134	8,460	1,246	7,214	5,411	10·0	541	560	10·0	10,000
Forbes: closed, spherangular, tin; open order	24·2	128	7,977	1,689	6,288	5,659	11·0	514	560	10·0	11,000
Blood: open, wooden; general	21·6	280	17,500	2,300	15,200	13,350	15·0	890	560	10·0	15,000

In the English and French equipment the pontoons were originally made of two sizes, the smaller and lighter for the “advanced guard,” the larger and heavier for the “reserve;” in both equipments the same size pontoon is now adopted for general requirements, the superstructure being strengthened when necessary for very heavy weights. The German army has an undivided galvanized iron pontoon, 24 ft. 6 in. long, handy as a boat, but of inadequate buoyancy for heavy traffic, with the result that the span has to be diminished and ipso facto the waterway obstructed. The Austrian and Italian pontoons are made in three pieces, two with bows and a middle piece without; not less than two pieces are ordinarily employed, and the third is introduced when great supporting power is required, but in all cases a constant interval is maintained between the pontoons. On the other hand, in the greater number of pontoon equipments greater supporting power is obtained not by increasing the number of supports but by diminishing the central interval between the pontoons. Within certain limits it does not matter whether the buoyancy is made up of a large number of small or a small number of large vessels, so long as the waterway is not unduly contracted and the obstruction offered to a swift current dangerously increased; but it is to, be remembered that pontoon bridges have failed as frequently from being washed away, as from insufficient buoyancy. In Austria efforts have been made to diminish the weight of the Birago equipment by the substitution of steel for iron. The present pontoon, in three pieces, is of steel, and 39 ft. 4 in. long, like the old pattern.

In the British army Colonel Blood’s equipment was later modified by the introduction of a bipartite pontoon designed in 1889 by Lieut. Clauson, R.E. Each pontoon is carried on one waggon with a bay of superstructure, and consists of two sections, a bow-piece and a stern-piece, connected together by easily manipulated couplings of phosphor bronze. Decks and “coamings” are dispensed with, and) the rowlock holes are sunk in a strong gunwale. The detachable saddle-beam, which receives the load on the centre of the thwarts, is made in sections, so as to form a continuous saddle of any length required. The baulks (or road-bearers) and chesses (or planks) remain unaltered, but chess-holders and chess-bearers are added for use in constructing light bridges for infantry in file. In this kind of bridge each pontoon section is used separately, with a roadway of chesses placed longitudinally four abreast. In the normal or medium bridge two sections, and in heavy bridge three sections are joined together. The chief advantages of the