In the former case, the narrow gauge, 20 in. with 14 lb. rails, is used,
with platform trucks and iron baskets 3 ft. 3 in. long.
The use of these wagons is particularly advantageous for clearing away
the sugar cane from the fields, because, as the crop to be carried off
is followed by another harvest, it is important to prevent the
destructive action of the wheels of heavily laden wagons. The baskets
may be made to contain as much as 1,300 lb. of cane for animal traction,
and 2,000 lb. for steam traction. In those colonies where the cane is
not cut up into pieces, long platform wagons are used entirely made of
metal, and on eight wheels. When the traction is effected by horses or
mules, a chain 14½ ft. long is used, and the animals are driven
alongside the road. Oxen are harnessed to a yoke, longer by 20 in. to 24
in. than the ordinary yoke, and they are driven along on each side of
the road.
On plantations where it is desirable to have passenger carriages, or
where it is to be foreseen that the narrow-gauge line maybe required for
the regular transport of passengers and goods, the 20 in. line is
replaced by one of 24 in.
The transport of the refuse of sugar cane is effected by means of
tilting basket carts; the lower part of which consists of plate iron as
in earthwork wagons, while the upper part consists of an open grating,
offering thus a very great holding capacity without being excessively
heavy. The content of these wagons is 90 cubic feet (2,500 liters). To
use it for the transport of earth, sand, or rubbish, the grating has
merely to be taken off. In the case of the transport of sugar cane
having to be effected by steam power, the most suitable width of road is
24 in., with 19 lb. rails; and this line should be laid down and
ballasted most carefully. The cost of one mile of the 20 in. gauge road,
with 14 lb. rails, thirty basket wagons, and accessories for the
transport of sugar cane, is 700l., and the total weight of this plant
amounts to 35 tons.
Owing to the great lightness of the portable railways, and the facility
with which they can be worked, the attention of explorers has repeatedly
been attracted by them. The expedition of the Ogowe in October, 1880,
that of the Upper Congo in November, 1881, and the Congo mission under
Savorgnan de Brazza, have all made use of the Decauville narrow-gauge
railway system.
During these expeditions to Central Africa, one of the greatest
obstacles to be surmounted was the transport of boats where the river
ceased to be navigable; for it was then necessary to employ a great
number of negroes for carrying both the boats and the luggage. The
explorers were, more or less, left to the mercy of the natives, and but
very slow progress could be made.
On returning from one of these expeditions in Africa, Dr. Balay and M.
Mizon conceived the idea of applying to M. Decauville for advice as to
whether the narrow-gauge line might not be profitably adapted for the
expedition. M. Decauville proposed to them to transport their boats
without taking them to pieces, or unloading them, by placing them on two
pivot trollies, in the same manner as the guns are transported in
fortifications and in the field. The first experiments were made at
Petit-Bourg with a pleasure yacht. The hull, weighing 4 tons, was placed
on two gun trollies, and was moved about easily across country by means
of a portable line of 20 in. gauge, with 14 lb. rails. The length of the
hull was about 45 ft., depth 6 ft. 7 in., and breadth of beam 8 ft. 2
in., that is to say, five times the width of the narrow-gauge, and
notwithstanding all this the wheels never came off the line. The
sections of line were taken up and replaced as the boat advanced, and a
speed of 1,100 yards per hour was attained. Dr. Balay and M. Mizon
declared that the result obtained exceeded by far their most sanguine
hopes, because during their last voyage, the passage of the rapids had
sometimes required a whole week for 1,100 yards (1 kilometer), and they
considered themselves very lucky indeed if they could attain a speed of
one kilometer per day. The same narrow gauge system has since been three
times adopted by African explorers, on which occasions it was found that
the 20 in. line, with 9 lb. or 14 lb. rails, was the most suitable for
scientific expeditions of this nature.
The trucks used are of the kind usually employed for military purposes,
with wheels, axles, and pivot bearings of steel; on being dismounted the
bodies of the two trucks form a chest, which is bolted together and
contains the wheels, axles, and other accessories. The total weight of
the 135 yards of road used by Dr. Balay and M. Mizon during their first
voyage was 2,900 lb., and the wagons weighed 5,000 lb. Hence the
expedition had to carry a supplementary weight of 3½ tons; but at any
given moment the material forming this burden became the means of
transporting, in its turn, seven boats, representing a total weight of
20 tons.
It is impossible to enumerate in this paper all the various kinds of
wagons and trucks suitable for the service of iron works, shipyards,
mines, quarries, forests, and many other kinds of works; and we
therefore limit ourselves to mentioning only a few instances which
suffice to show that the narrow gauge can be applied to works of the
most varied nature and under the most adverse circumstances possible.
It therefore only remains to mention the various accessories which have
been invented for the purpose of completing the system. They consist of
off-railers, crossings, turntables, etc.
The off railer is used for establishing a portable line, at any point,
diverging to the right or left of a permanent line, and for transferring
traffic to it without interruption. It consists of a miniature inclined
plane, of the same height at one end as the rail, tapering off regularly
by degrees toward the other end. It is only necessary to place the
off-railer (which, like all the lengths of rail of this system, forms
but one piece with its sleepers and fish-plates) on the fixed line,
adding a curve in the direction it is intended to go, and push the
wagons on to the off-railer, when they will gradually leave the fixed
line and pass on the new track.
The switches consist of a rail-end 49 in. in length, which serves as a
movable tongue, placed in front of a complete crossing, the rails of
which have a radius of 4, 6, or 8 meters; a push with the foot suffices
to alter the switch. There are four different models of crossings
constructed for each radius, viz.: