This is an ingenious proposition for utilizing a modification of the wire
tramway system for overcoming obstacles (while retaining the ordinary
wire tramway or any light railway on other parts of the line), made by
Mr. Charles Ball, of London.
The flexible girder tramway is an improved system of constructing a
modification of the well known and extensively used rope or wire tramway,
and it is claimed that it will revolutionize the transport of the
products of industrial operations from the place of production to the
works or manufactory, railway station, shipping ports, or place of
consumption; and that in the result the introduction of the flexible
girder tramway will in many cases enable profits to be earned in
businesses which have hitherto been unremunerative. It is declared to be
at once simple, cheap, durable, and efficient. The improvement consists
in the employment, in addition to the usual tram wire (a hempen rope, a
wire rope, or a metallic or other rod), along which the load is
transported, of a second or suspension wire or rope to which the tram
wire is connected by tension rods or their equivalent at intervals
between the rigid supports or piers, the object being to diminish or
distribute the sagging or deflection of the tram wire, and thus lessen
the steepness of the gradients over which the load has to be transported.
The combined tram wire, tension rods, suspension wire, and accessories
are, for convenience, designated a "flexible girder."
Another improvement consists in using, when a double line is employed,
stretchers or crossheads to keep the flexible girders nearly parallel to
each other, so that when necessary the load to be transported may be
suspended from or borne by both tram wires jointly or simultaneously,
thus permitting a load of greater weight than that for which each single
tram wire is intended to be carried over the system. One indisputable
claim for confidence in the flexible girder principle is said to be that,
although the peculiar combination of parts constitutes a striking and
valuable novelty, it contains nothing that has not been proved by the
experience of years--nay, generations--to be useful, economic, and
reliable. The usual practice followed in erecting suspension bridges is
applicable in mounting the line, and the carriers, supports, and
carriages may be of any of the usual forms. For the rapid removal of
limited loads wire tramways are in universal favor, and are recognized
not only as very economic and quickly constructed, but also as being in
many cases the only means of transport available except by the adoption
of elaborate and costly engineering works.
It has, it seems, been suggested by some who have examined the
construction of the flexible girder tramway for mineral and produce
traffic that it would be an additional advantage if arrangements were
made for the carriage of small loads--half a dozen or so--of passengers,
the primary intention being to carry the workpeople backward and forward
between comparatively inaccessible mines, works, or plantations and a
neighboring village or town. Compared with every other system where the
line over which the load travels is elevated, the flexible girder tramway
is claimed to possess many advantages--the center of gravity is kept well
down, the liability of the wheels leaving the line is reduced to the
minimum, the gradients are the easiest that can be obtained, there is an
entire absence of jolting and extremely little vibration, and the motion
is altogether smooth and regular; yet it is very questionable whether,
when human life is at stake, any but an ordinary ground line should be
relied upon. A living freight is far more liable than a dead freight to
move during the journey; and as the safety of all overhead lines depends
upon what is scientifically designated "unstable equilibrium," the
flexible girder tramway is not recommendable for passenger lines,
although it can, of course, be fitted for passenger traffic, a suitable
vehicle and ten or a dozen good stout workmen coming well within a
two-ton load, which can be readily carried.
[Illustration: BALL'S FLEXIBLE WIRE TRAMWAY.]
Rope traction or animal traction--practically speaking--is alone
available for wire tramways (that is to say, if the trains are each to be
propelled by its own locomotive--whether steam, springs, or
electricity--the cost of construction and maintenance becomes so serious
that overhead lines, however well designed, are no longer economic); and
experience gained with rope traction in numerous collieries in the North
of England and Lancashire districts--where it is highly appreciated--has
shown that, all circumstances considered, the endless rope is preferable.
The chief objection urged against wire tramways as hitherto constructed
has been that the "sag" of the rope has sometimes caused annoyance to
those using the property passed over, and has always added much to the
cost of traction, owing to the increased power required for moving the
load; this has also resulted in vastly increased wear and tear and the
rapid deterioration and destruction of the wire rope. The flexible girder
system so reduces the "sag" that the maximum economy and durability are
obtained, and the gradients over which the load has to travel can be made
as easy and regular as those upon an ordinary railway. This advantage
will be the more readily appreciated when it is considered that with a
given load on a gradient of 1 in 30 the resistance due to gravity alone
is 200 per cent. greater than on a gradient of 1 in 150, and that the
retardation and wear and tear due to friction, greater curves, and
imperfections increase still more rapidly with increase of gradient, soon
rendering the old sagging wire line practically worthless.
To construct an entire line of flexible girders would be not only
unnecessary, but so costly as to neutralize any advantage which it may
possess, yet for surmounting occasional obstacles the claim made for
it--that it will sometimes permit of a line otherwise impracticable being
cheaply made--seems justified. One can readily imagine a light narrow
gauge line costing £1,000 per mile being laid, for example, between a
mine and the shipping place, and that a swamp, river, or valley would
cost more to bridge over than the whole line besides. If at this obstacle
the trucks or carriages could be lifted bodily, passed along the flexible
girder, and again placed on the line the other side of the obstacle, the
advantage to be derived is obvious; and as the flexible girder is really
little more than a suspension bridge _minus_ the platform, and having but
two suspension wires, the cost and the difficulties should both be very
small.--_Industrial Review_.
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