The French Bridging Operations across the Danube in 1809: Technical Details of the Second Attempt

Editor's Note: The source of this document is: Douglas, Howard. An Essay on the Principles and Construction of Military Bridges and the Passage of Rivers in Military Operations 2nd edition; London : Thomas and William Boone; 1832. Appendices Pages 24 - 28

"Bridge in one Piece across the Danueb, in 1809"

This extraordinary bridge, (#4, Plate 6) and partly shown in Figure 2, Plate 6, in detail, was composed of 14 Austrian pontoons, (Figures 5, 6, Plate 5).

The bridge was formed in 4 pieces or rafts; 2 of the rafts were of 4 pontoons, and 2 of 3 pontoons each. There were but 3 balks to each bay, as the bridge was only for the passage of the infantry. The boats were placed about 34 feet distant from centre to centre; the bays were consequently about 28 feet wide, each.

The balks overlapped each other, and rested on both gunwales of the boats, projecting about a foot on each side; each pair of balks was bolted together in the middle of the boat, and kept at equal distances from each other, by small blocks of wood placed between, on the gunwales, and held together by cleats butting against the exterior balks, and pinned to the gunwales. The balks were about 42 feet long and 8 inches square, and all clamped to the sides of the boats by iron clamps.

The following is a list of the materials used int he construciton, viz.

Forty-five balks, of which 3 were for connecting the boats with each other, and 6 for the ramps, or for connecting the end of the boats with the banks. Thirty pieces of scantling, or balks, each 35 feet long, and 6 inches square, for racking down the planks or flooring of the bridge at the sides; their ends, cut so as to overlap each other, were bolted together -- the bolt passing through the flooring and the balk below.

Fifteen traverses, or cross-pieces of wood, mortised to receive the balks, into which they were also let, so that when properly fixed their upper surfaces were flush with the upper surfaces of the balks. They were placed in the middle between 2 boats, to bind the balks together, and also to keep them at the proper distance from each other.

Fifty-six small blocks of wood, placed on the gunwales of the boats, 4 to each boat, between the balks, to keep them at equal distances from each other.

Fifty-six cleats, 4 to each boat, nailed to the gunwales of the boats, butting against the exterior balks, and thus binding the whole together.

Fifty-zix braces, 4 to each boat, 9 feet long, and about 4 inches square, one end bolted to the gunwales, the other end bearing against, and bolted to the exterior balks, by which they were kept in the proper position.

Five hundred and ten planks, 7 feet long, 1 foot road, and 1 1/2 inch or 2 inches thick, for flooring.

Eighty-four clamps, 6 to each boat, for securing together each pair of balks, and for fastening them to the exterior sides of the boats.

Forty-two bolts, with nuts, passing through each pair of balks, fore and aft, in the middle of each boat.

Two sheerlines, or ropes extending from one bank to the other, passing through the rings in the heads and sterns of the boats.

The rafts had separate sheer-lines, distinct from each other, but so arranged that they might be readily joined together, or cast loose. This was accomplished by having an eye-splice at one end, through whihc the plain end of the other line was passed and made fast.

The spring lines were arranged in a similar manner, and passed through holes in the sides of the boats, under the gunwales.

Two long guy ropes, of 100 fathoms each, for swinging the bridge, were fixed to the further end, and eased off when the bridge was swinging, so that its motion should be moderate and uniform.

Ten anchors, of which 7 were stream anchors being 1 anchor to every 2 boats.

Ten cables and buoys.

Two crab capstans, for hauling tight the hawsers at the heads and sterns of the boats.

Ten large pickets shod with iron.

Twenty-eight oars.

Fourteen boat hooks.

Scoops, for bailling, hand pumps, besides spare rope, straps, lashings, etc., etc.

In taking the bridge down the narrow channel where it was constructed, in order to shorten it as much as possible, and to enable it to follow the bend of the stream, the rafts were attached to each other by ropes, and the fixed balks of the exterior boat of each raft placed on a roller, (Figure 2, plate 6), laid on the flooring or balks of the end boat of the adjoining rafts, so that turning or winding, the balks might move from side to side on the roller, attention being paid not to let them get off i.

When the direction of the anrrow channel became straight, and led directly into the main branch of the river, the different parts, or rafts, were put together. One squad of pontooners arranged and set the balks in their places, and secured them to each other; (Note 1) another squad fixed the clamps which fastened the balks to the gunwales, and arranged and fixed the blocks of wood and the cleats; while a third squad arranged the braces or oblique shores, laid the flooring, and then bolted the racking balks. Whilst this was doing, the bridge was allowed to descend, attended by other pontooners, divided into 6 squads. The 1st squad caried the ends of the sheer lines, ready to fix them on the right, or occupied bank of the river. The 2nd squad carried the guy-ropes of 100 toises each, one end of which was fixed tot he end of the bridge which was to reach the opposite bank: when the bridge was to be swung across, the rope was passed round a tree, and the men of the squad, holding-on the other part of the rope, eased it off as the bridge was swinging, and thus kept it straight and made its motion uniform. The 3d squad had charge of the anchors, to cast them at the proper times. The 4th squad, provided with long boat hooks, modified and regulated the movement of the bridge while it was swinging. The 5th squad, in a boat, attended the bridge as a reserve, to assist or strengthen any other squad. The 6th squad attended in small boats, with anchors, ready to be applied at any points where the bridge, in sqinging, might seem likely to bend.

When the bridge arrived in the main branch of the river, it was allowed to descend for about 250 yards along the right or near bank, after which it was swung across in the following manner.

The 2st squad fixed their sheer lines to 2 trees.

The 2d squad, having passed their guy round a tree, pushed off the end of the bridge which was to reach the opposite bank, being assisted int he operation by the 4th squad, with their boat-hooks.

The 3d squad cast the anchors in succession, and brought the cables to the boat opposite to the anchor, where they veered away cable, or held-on, as circumstances required.

The operation of swinging the bridge was performed in 4 or 5 minutes; and at about 11 o'clock at night a division of infantry passed.

Pickets were driven for the sheer and spring lines, and capstans fixed on the enemy's side, or left bak of th river, whilst the troops were filing across.

Notes:

1. My information states that the balks of the several portions of this bridge were connected with each other by clamps of iron and wedges, the wedges being placed at the sides, instead of the tops of the balks: this indeed is a much preferable mode of fastening, being strongerand more readily adjusted and executed during the descent of the bridge, then by bolting the end balks together, an operation, which on account of the nicety required in bringing bolt-holes opposite to each other, and in retaining them in that position whilst the bridge is in motion, would be attended with some difficulty and uncertainty.

Placed on the Napoleon Series: October 2004

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