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sink-me
Uncle Sam's Tom Thumb Navy
Aircraft carriers lost in battle might still be alive if they had been able to
dodge a little faster, pivot out of the path of an enemy bomb or torpedo. They needed
the footwork of a boxer dodging a fist. Maneuverability is the surface vessel's
best answer to attack.
Our new flattops have it. The new Lexington, Yorktown and other carriers just
built or building can play tag with enemy tinfish like a frisky waterbug.
For these new seagoing airfields were built to designs tested and perfected in
the Navy's David W. Taylor Model Basin at Carderock, Md. The intricate details of
design of the 1943 carriers are a secret our enemies would like to break open. What
they do know is that our naval architects demonstrated exactly how these ships will
behave in action long before the keel was laid - for the design was created and
proved in 20-foot models made of wood. At Carderock 75 skilled woodworkers carving
with hand tools 200,000 board feet of western pine per year serve as the control
key to the battle supremacy of American ships. A $400 western sugar pine model may
save years of time, millions of dollars and thousands of fighting men's lives.
The Navy's model basin, one of 40 in the world, is the newest, built to produce
the greatest test accuracies. Our allies, with model basins of their own, send over
plans of their fighting ships to be modeled and tested at Carderock.
At all foreign test basins the models are made of paraffin. Ours are made of
sugar pine, Idaho white and Ponderosa - all western white pines. There could be
no worse military practice than to tie a key operation to a material wholly controlled
by a potential enemy. We control the source of western pine, available in no other
part of the world. American operators grow it on 10,000-acre tree farms. Other nations
make shift with paraffin models.
At left, hoisting a model hull from the basin after a test. Below, model
builders put finishing touches on a miniature ship
U. S. Navy photos
Until about 1870 no one could know, before a ship had its trial runs, just how
it would perform - its speed, maneuverability or cost of operation. Then William
Froude, an English engineer, began building models to scale and amassing comparison
data by towing them at various rates of speed. Performance depends on size, sleekness
and shape of the hull; on weight, superstructure arrangement, power plant, shaft
and propeller design. Froude found that a model built to exact geometrical scale
and towed to a certain ratio of speed would tell the designer what the full-sized
ship would do. Some nations were slow in adopting his teachings. A few years before
the last war visitors saw tied up at a Hamburg, Germany dock a brand new luxury
liner consigned to rust. Its first transatlantic trip proved it could not meet competitive
speeds and earn its fuel. Model tests would have averted that failure.
The Carderock basin is a massive laboratory embracing five towing canals. its
monolithic concrete walls are joined directly to bed rock, helping to insure accuracy
by virtually eliminating vibration.
The famed battleship Oregon was scrapped recently, but it lives in a
Carderock model
Women are building scores of ship models on 1 to 500 scale for identification
study
A layman untutored in marine mathematics might guess that a model one-tenth the
size and with one-tenth the power of a full-sized ship would have the same rate
of speed as the large vessel. That is not the case. Froude evolved a formula of
"corresponding speeds." If a model is built exactly to geometric scale and towed
under laboratory conditions, the "corresponding speed" is the square root of the
ratio of the length of the model to the length of the full-sized ship, multiplied
by the given speed of the large craft. A 14-foot model towed at 3.85 knots has the
corresponding speed of a 500-foot ship running at 23 knots. A 10-foot model of a
100-foot ship, towed at 20 knots, corresponds to a ship speed of 63 knots. By similar
computations in model tests the engineers learn how much resistance to the water
the large ship will offer at any given speed and how much propulsive power is necessary.
Here, in miniature, is the Japanese fleet - the carrier Soryu at top
- reproduced to help Navy airmen and deck officers recognize them
Water resistance consists partly of friction between the water and the subsurface
hull, partly of residual resistance caused by waves, eddies and other disturbances
created by the hull .form. Frictional resistance can only be decreased by producing
a smoother hull surface and decreasing the underwater area. The residual resistance
can be lessened by changing hull design.
When Congress authorized the heavy cruisers of the Salt Lake City class, requirements
were 10,000 tons displacement with speed as high and better sea-keeping characteristics
than any existing destroyers. That problem was the model tester's dish. A series
of wood mod el s were tested, changed and tested again, and came out with an entirely
new underwater stern, a new mid-ship section and a bulb bow. Full-sized vessels
made 32 knots.
This is the towing carriage on Carderock's deep basin. The tower is part
of electric power supply system
That is the sort of development born of test-model practice, which is producing
new ships for this war. Destroyer escorts are in point. They are new, designed expressly
for convoy duty, created to quell U-boats. Equal in fighting power to last war's
destroyers, they are smaller, much faster, and can spin almost within their own
length to catch a dodging submarine.
Almost at the other extreme of new design are invasion ships, big armed vessels
built to carry battle cargo. Some carry tanks. Arrived at a hostile shore, down
goes. the front end of the vessel's hold to make a steel bridge over which armored
land fortresses roll to blast out a beachhead. Somewhat smaller vessels are designed
to put foot soldiers ashore with equal speed. The first of these got their baptism
of fire in North Africa.
Demands on the designers of the new aircraft carriers were enormous. Decks big
enough to deploy more than 100 warplanes. Elevators that can deliver planes from
storage deck to flight top in less than 10 seconds. More spacious holds to carry
more gasoline, protected with new types of equipment and better fire control, all
adding to deadweight. Heavier underwater armor. Altogether, a ship with displacement
raised to 25,000 tons, able to make longer voyages and carry more airplane fuel
than any before designed, and be the fastest and most maneuverable carriers afloat.
The woodworkers who make the Carderock models are all old patternmakers. A hull
model is built up in rough outline of two-inch thick planks pinned together with
wooden dowels. Then it is taken down and the wood layers smeared with waterproof
resin glue applied hot. Reassembled, the block is placed in a 1,200,000-pound press;
after 16 hours in the press it is solid. Then it is blank-contoured in a profiling
machine, the only machine tool used. The rest of the modeling is skilled handwork
with gouge, chisel, spoke shave, plane, sandpaper.
Skilled patternmakers using hand tools carve geometrically accurate models
in western pine of combat and merchant ships
Once a model has been perfected it is kept on file until the ship it represents
is out of commission. Wood models can be stored safely for decades without distortion.
The standard model is 20 feet long; some have been 60 feet long. The 20-foot mod
e 1 weighs a ton. Equipped with motors serving also as dynamometers, test propellers,
and driven at full model speed of six knots (corresponding to 33 knots for a 600-foot
ship) the rudder is turned full over and the model brought up after a 90 degree
turn, with the bow striking the concrete wall. That would disintegrate a paraffin
model.
Ballasting a model to bring it to proper waterline before giving it a
self-propulsion trial
The test equipment consists of five basins - long, narrow canals - with towing
carriages and dynamometers. The largest is 963 feet long, 51 feet wide, 22 feet
deep. Accurate to thousandths of an inch, the carriage rail actually follows the
curvature of the earth so there is no variation from end to end in gravity pull.
Other basins are especially for tugboats and river craft, high speed motorboats,
naval flying boats and the like. In one, turning tests are made in the dark, with
lights hung on the model's bow and stern and a movie camera recording the performance.
Air resistance of a ship's superstructure can be tested by towing the model upside
down.
Three-fourths of the work today is secret. In the model shop, woodworkers are
carving forms for antisubmarine warfare, submarine targets, minesweeping devices.
The cargo ships hatching in yards throughout the nation were incubated from Carderock's
wooden models. Here a foreign destroyer is being scaled in a 3D-foot model, big
enough for tests that will find its weaknesses in detail. There a standard warship
will tryout a new superstructure. And here is a new speedboat offered by a famous
American designer, its hull shape suggesting that it may challenge the speed of
Navy aircraft. In one workshop girls are building recognition models to teach our
sailors and fliers to identify ships at a distance by a split-second glance.
The fighting Navy America is swiftly building to sweep the seven seas clean of
Axis craft got its auspicious start in pine models cruising the vaulted indoor canals
of Carderock.
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