Considerable attention has been given for some years past to the subject of
floating pontoon docks by Mr. Robert Turnbull, naval architect, of South
Shields, Eng., who has devised the ingenious arrangement which forms the
subject of the annexed illustration. The end aimed at and now achieved by
Mr. Turnbull was so to construct floating docks or pontoons that they may
rise and fall in a berth, and be swung round at one end upon a center post
or cylinder--nautically known as a dolphin--projecting from the ground at
a slight distance from the berth. The cylinder is in deep water, and,
when the pontoon is swung and sunk to the desired depth by letting in the
necessary amount of water, a vessel can be floated in and then secured. The
pontoon, with the vessel on it, is then raised by pumping out the contained
water until she is a little above the level of the berth. The whole is then
swung round over the berth, the vessel then being high and dry to enable
repairs or other operations to be conducted. For this purpose, one end of
the pontoon is so formed as to enable it to fit around the cylinder, and
to be held to it as to a center or fulcrum, about which the pontoon can be
swung. The pontoon is of special construction, and has air-chambers at the
sides placed near the center, so as to balance it. It also has chambers at
the ends, which are divided horizontally in order that the operation of
submerging within a berth or in shallow water may be conducted without
risk, the upper chambers being afterwards supplied with water to sink the
pontoon to the full depth before a vessel is hauled in. When the ship is in
place, the pontoon with her is then lifted above the level of the berth in
which it has to be placed, and then swung round into the berth. In some
cases, the pontoon is provided with a cradle, so that, when in berth, the
vessel on the cradle can be hauled up a slip with rails arranged as
a continuation of the cradle-rails of the pontoon, which can be then
furnished with another cradle, and another vessel lifted.
It is this latter arrangement which forms the subject of our illustration,
the vessel represented being of the following dimensions: Length between
perpendiculars, 350 feet; breadth, moulded, 40 feet; depth, moulded, 32
feet; tons, B. M., 2,600; tons net, 2,000. At A, in fig. 1, is shown in
dotted lines a portion of the vessel and pontoon, the ship having just been
hauled in and centered over the keel blocks. At B, is shown the pontoon
with the ship raised and swung round on to a low level quay. Going a step
further in the operation, we see at C, the vessel hauled on to the slipways
on the high-level quay. In this case the cylinder is arranged so that
the vessel may be delivered on to the rails or slips, which are arranged
radially, taking the cylinder as the center. There may be any number of
slips so arranged, and one pontoon may be made available for several
cylinders at the deep water parts of neighboring repairing or building
yards, in which case the recessed portion of the pontoon, when arranged
around the cylinder, has stays or retaining bars fitted to prevent it
leaving the cylinder when the swinging is taking place, such as might
happen in a tideway.
[Illustration: Fig. 1. IMPROVED FLOATING PONTOON DRY DOCK.]
The arrangements for delivering vessels on radial slips is seen in plan at
fig. 2, where A represents the river or deep water; B is the pontoon with
the vessel; C being the cylinder or turning center; D is the low-level
quay on to which the pontoon carrying the ship is first swung; E is the
high-level quay with the slip-ways; F is an engine running on rails around
the radial slips for drawing the vessels with the cradle off the pontoon,
and hauling them up on to the high-level quay; and G shows the repairing
shops, stores, and sheds. A pontoon attached to a cylinder may be fitted
with an ordinary wet dock; and then the pontoon, before or after the vessel
is upon it, can be slewed round to suit the slips up which the vessel has
to be moved, supposing the slips are arranged radially. In this case, the
pivot end of the pontoon would be a fixture, so to speak, to the cylinder.
The pontoon may also be made available for lifting heavy weights, by
fitting a pair of compound levers or other apparatus at one end, the
lifting power being in the pontoon itself. In some cases, in order to
lengthen the pontoon, twenty-five or fifty foot lengths are added at
the after end. When not thus engaged, those lengths form short pontoons
suitable for small vessels.--_Iron_.
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