Evening star. [volume] (Washington, D.C.) 1854-1972, 1897-10-30

only that part and mild percentage of the
rest of the dock need be exhausted. If
vessel be unable to reach a craving dock
by her own power she can never be light
cred in. for the pontoons could not get her
through the gate. And further, it may be
said that the major part of the materials
that constitute a craving dock go rather
to hold the dock down and in place, when
emptied, against hydrostatic pressure from
without than to meet the simple require
ments of strength. In a floating dock the
thing desired is that it shall rise by virtue
of it's own natural buoyancy; and. instead
of sinking. the floating dock actually sup
ports the equivalent of the greater part of
that weight which serves merely to hold
craving dock of like displacement In place.
This means a helpful buoyancy of hundreds
upon hundreds of tons instead Of a useless
dead weight of like magnitude.
Various Types.
These types of tine floating dock are, first,
the off-shore dock, and, second, the self
docking. floating craving dock. The Off
shore dock consists, principally, of three
parts. viz: the dock proper. the shore work
ard the booms Orders which connect
the dock to the shore. The dock itself con-
sists of a number of long steel boxes or
pontoons, having an endwise appearance,
like the letter L, and 1t is, so to speak, in
the laps of these LIS that the ship rests.
The part of the l. that lies upon the water
is the lifting part proper, and is called the
pontoon, while the chief function of the
vertical part or wall, as it is called, Is to
give stability to the dock during the time it
is being submerged In the wall, and on it,
too, are placed the controlling mechansmS
for the pumps, the derricks. the shores that
brace the inner side of the vessel, and the
bilge blocks, which support the bottom of
the ship. The interior of each pontoon Is
strongly built, and reinforced so as to bear
safely the weight of a ship. and, to give
more perfect control of the water within,
Is subdivided into a number of separate
water-tiSht compartments, each under in
dependent control. In this way the rush of
water from one end of the pontoon to the
other in case of slight heeling of the dock
is prevented and the mass of water is
handled without jar, and practically as so
is constructed on the same general prin-
ciple, but is lighter, because it does not
have to bear the same strains: From the
valve house on the upper deck of the dock
the valve of every compartment is under
the direct control of one man, who by
means of speaking tubes, can also direct
the engineer in charge of the pumps, while
a conspicuous scale Of feet, close to each
end of the wall, marks the slightest varia-
ton or inequality of trim. The shore work
consists of series Of upright columns,
strongly braced SO as to resist a consider
able effort to tip on the part of the dock,
this helpful force being transmitted back
to the dock through the parallel hinged
booms or girders. which hold the dock I'M
der complete control. while permitting 1t to
rise and fall through all its intended scope.
The top booms are not fastened directly to
the columns, but to large pear-shaped
plates, pivoted there instead. To the pear
shaped plates are attached heavy weights
and as the tipping stress of the dock tends
TO push the booms against the top of the
columns the weights act as efficient coun-
terpoise. By watching the positions of the
pear-shaped plates. the valve man can see
just how to regulate the admission or the
exhaust of water.
Advantage in Streams.
As a safeguard against breakdown and
complete disablement, the injury of one
pontoon effects the efficiency Of the dock
or ly to the extent Of it's own withdrawal
The rest are firmly coupled together and
work can go on to the full capacity of the
remaining pontoons Each pontoon has an
average length of about $50 feet and when
united form a thoroughly stable foundation
for the heaviest craft. The off-shore dock
recently built for Hamburg Is capable of
lifting 1900 ton ship; and it is safe to
say the whole operation could be performed
considerably within half an hour To do
the same thing in craving dock would in
volve quite two hours. Another advantage
peculiar to the floating dock is that, While
1t may not be able to lift beyond its own
capacity. 1T can accomplish much within
that scope, and 10000 ton ship that may