The midland journal., 1915-05-07
DRYDOCkS.
Where the Largest Warships Can
Be Repaired In Safety.
HUGE BASINS OF CONCRETE.

Into These the Vessels Are Eloated and
shored Up as the Gates Are Closed
and the Water Pumped out-FIoatino
Docks and How They Are Used.
There is no such thing as a perfect
antirfouling composition, and probably
there never viii be.
By "anti-fouling' we mean a solu-
tion which, applied to the bottom of a
ship, will keep her clean for an indefl-
mite period
True, vessels can now keep the sea
for months ON end without getting foul
enough to seriously diminish their
speed, but in the long run their bot
toms become weed grown, and they
are obliged to go into drydock and be
scraped and, cleaned and repainted.
In old days. when warships were no
larger than the steam launches which
now hang on Dreadnought's davits,
the seamen did this work themselves.
They ran the galley on to some con-
venient beach, hauled her out, tipped
her on one side on the sand. scraped
her and caulked her seams.
Even in the eighteenth century Cap
tain Cook "careened" his vessel in a
tidal creek on the Australian coast and
did necessary repairs. The enormous
warships of today require very differ
ent handling, and it is for their use
that dockyards are fitted with "dry"
mr. ssrrfsov VII rlrrN NA
sions.
A drydock Is a huge basin excavated
in the ground. It is lined first with
masonry of immense thickness, and
this in turn is coated with thousands
of tons of concrete.
The first great requisite of dry
dock is to be dry, and as it is always
cut in low, swampy ground, with the
bottom far below low tide mark, this
is the great difficulty before its build
ers.
The bottom Is quite fiat. The sides
run up In steps-enormous steps, each
about yard high, not the sort Of stair
case to run down in hurry.
These steps are known as .saltars,"
and they have two separate purposes
first for supporting the workmen's
scaffolds, the second and more impor-
tant for the fixing Of the shores"
Shores are the great balks Of timber
which hold a vessel upright in drydock.
A drydock does not usually open
straight out of the sea or harbor. More
often there is a wet dock between.
The reasons are that vessel can then
be docked at any state of the tide and
also that there is less pressure on the
great watertight gates Of the drydock.
The actual process of docking in dry
dock is simple enough. The drydock
is filed with water, the ship is foated
in, the gates close behind her; then the
water is pumped out by means of pow
erful steam pumps.
Along the bottom Of the dock runs In
straight line a row Of keel blocks on
which the keel of the vessel rests. As
the water is pumped away an army of
workmen fix the shores in position.
This is task which requires great
care. Not so very long ago an 5000 ton
cruiser which was being drydocked at
one Of the southern dockyards In Eng
land was so carelessly shored up that
she slipped and toppled over.
The damage was appalling. The huh
Of the ship was badly injured 1t cost
many thousands of pounds to repair
her.
There are also floating craving docks.
There is one at Portsmouth with an
area Of two and one-quarter acres and
a lifting capacity Of $4,000 tons. It is
700 feet long and IA feet wide. Its
cost was f264,000.
The beauty of floating dock is that
If vessel is badly damaged the dock
can go to the ship instead of the ship
to the dock. Also even If the ship is
heeling over. so that she could not be
passed through the gates of stone
dock, the floating dock can take her.
The floating dock is simply a large
cradle built in series of watertight
compartments which can be filed or
emptied at will. 1t was invented by
George Rennie in 1866. BY means of
floating dock a large warship can be
raised high and dry within three hours.
Aboard, life goes on as usual. while
the sailors floating home stands shored
up In dry dock. Her decks are just
about level with the top of the sides.
but between them Sand firm ground
yawns chasm at least forty feet deep.
During wartime the work of clean
ing and repainting the under part Of
the hull goes on night and day, and a
job that usually takes fortnight may
be completed within four or even three
days.-Pearson's Weekly.
Are You RhenmaticF-Try SIoan's.