The distance between the centres of two boats in position is called a bay. The distance between the boats is thirteen feet ten inches. The distance between the side-rails is eleven feet, this being the width of the roadway.
AN ANGLE OF FORT HELL (SEDGWICK) SHOWING GABIONS, CHEVAUX-DE-FRISE, ABATIS AND FRAISE. FROM A PHOTOGRAPH.
An abutment had to be constructed at either end of a bridge, which was generally done by settling a heavy timber horizontally in the ground, level with the top of the bridge, confining it there by stakes. A proper approach was then made to this, sometimes by grading, sometimes by corduroying, sometimes by cutting away the bank.
The boats, with all other bridge equipage, were carried upon wagons, which together were known as the Ponton Train. Each wagon was drawn by six mules. A single boat with its anchor and cable formed the entire load for one team. The balks were loaded on wagons by themselves, as were also the chesses, and the side-rails on others. This system facilitated the work of the pontoniers. In camp, the Ponton Train was located near army headquarters. On the march it would naturally be in rear of the army, unless its services were soon to be made use of. If, when the column had halted, we saw this train and its body-guard, the engineers, passing to the front, we at once concluded that there was “one wide river to cross,” and we might as well settle down for a while, cook some coffee, and take a nap.
In order to get a better idea of ponton-bridge laying, let us follow such a train to the river and note the various steps in the operation. If the enemy is not holding the opposite bank, the wagons are driven as near as practicable to the brink of the water, unloaded, and driven off out of the way. To avoid confusion and expedite the work, the corps is divided up into the abutment, boat, balk, lashing, chess, and side-rail parties. Each man, therefore, knows just what he has to do. The abutment party takes the initiative, by laying the abutment, and preparing the approaches as already described. Sometimes, when the shore was quite marshy, trestle work or a crib of logs was necessary in completing this duty, but, as the army rarely approached a river except over a recognized thoroughfare, such work was the exception.
While this party has been vigorously prosecuting its special labors, the boat party, six in number, have got a ponton afloat, manned it, and ridden to a point a proper distance above the line of the proposed bridge, dropped anchor, and, paying out cable, drop down alongside the abutment, and go ashore. The balk party are on hand with five balks, two men to each, and having placed these so that one end projects six inches beyond the outer gunwale of the boat, they make way for the lashing party, who lash them in place at proper intervals as indicated on the gunwales. The boat is then pushed into the stream the length of the balks, the hither ends of which are at once made fast to the abutment.
A WOODEN PONTOON BOAT. FROM A PHOTOGRAPH.