THE PONTON.
The “Ponton” is another kind of ferry boat.
The larger sized craft are raised forward and aft to facilitate the passage. The bow and stern, which are broad and flat, carry a movable part called the “Koebrug” (cow bridge) to facilitate taking horses, cattle and carts on board. These movable outside bridges are lowered and raised by two balanced levers, one on each side. By bearing down on them, the fore bridge is raised a little above the horizontal. The lever is then made fast. After crossing the river, the bridge is dropped and rests on the approach. The slope of the bridge must not be too great, nor should the movable part be too long, otherwise it would be unmanageable.
It follows from what precedes, that there exists, for a good approach, a certain relation between the slope of the ramp, the length of the movable bridge and the draught of the ferry-boat.
As a general rule and for ordinary pontoons, the most favorable slope for the ramp is 1 in 8.
An easier slope makes too sharp an inclination for the movable bridge; a steeper slope, which would make the bridge more nearly horizontal, would make, on the other hand, too difficult an approach for wheeled vehicles.