Side haul railway dry docks
Ship transfer machinery
Chains, rollers and maintenance
Bridles roller system
Restoration & enlargement
Vertical lifting vs. inclined ways
Some parts of a railway dry dock,
such as the pile foundation and the machinery foundation, do not
deteriorate as the dock is used. Others - the hauling machine,
electric motor, and underwater timber ways - can last up to 100
years and thus outlive several times the useful life of the cradle,
chains, roller system, and rail plates. Since the more durable
parts represent over half the cost of a new facility, it is economical
to rebuild or restore older facilities, replacing inadequate parts
with improved, modern equipment.
As an example, the older docks had timber cradles. When one of
these requires replacement, we find it is more economical today
to use a steel frame, which reduces the weight and therefore increases
the useful capacity. A 1000-ton wooden cradle for a 5000-ton dock
might be replaced by one in steel weighing 600 tons, raising the
lifting capacity to 5400 tons.
In a rebuilding project we often increase the capacity additionally
by making the new cradle and the track longer - the load per lineal
foot cannot exceed the foundation's original capacity, but the
total load can go up (larger hauling chain may also be required)
This approached helped Norfolk Shipbuilding and Drydock Corp.
to increase the capacity of its large railway from 4500 to 5200
It is sometimes possible to extend the range of haulable vessels
by widening the cradle, without foundation strengthening or other
major modifications. The Ferguson Industries 2000-ton railway
at Pictou, Nova Scotia was first widened to take North Umberland
ferries and then lengthened to take CNR ferries, both without
any long down time of the dry dock.
It may be worthwhile to reinforce the foundation and provide
stronger track and cradle structure for greater load per foot
and perhaps greater total weight. In the case of the 5000-ton
railway dry dock of Marine Industries LTD. At Sorel, Quebec, the
capacity per lineal foot was increased form 14 to 19 tons per
foot. The reconstruction consisted largely of track and foundation
reinforcement, with a cradle having heavier, stiffer beams.
As a wartime facility it was intended to haul river vessels and
to launch hulls of new vessels built in the adjacent transfer
area. Today it must be capable of launching vessels finished and
ready for sea or of drydocking ocean ships with much heavier load
per foot of length than before. In this case the transfer ways
also required reinforcement.
Next: Vertical vs inclined