TAYLOR MODEL BASIN—HOWARD 243 
0.01 pound but rugged enough to handle the forces on large, 30-foot 
battleship models at full test speed. 
Two variable-pressure water tunnels, designed primarily for testing 
model propellers but also used extensively for special hydrodynamic 
tests, are among the unusual facilities. Each water tunnel consists of a 
closed duct circuit arranged in a vertical plane, in which water is 
circulated at a known speed. In the lower limb of the apparatus is a 
motor-driven impeller which circulates the water, and in the upper 
limb is the test section, fitted with glass ports for visual and photo- 
graphic observation of the propeller being tested in a jet of water of 
uniform velocity and turbulence. The diameter of the jet nozzle is 
12 inches for one of the water tunnels, and 24 inches for the other. 
The model propeller is mounted on a motor-driven shaft projecting 
into the test chamber. The thrust and torque of the propeller at vari- 
ous speeds of revolution are measured by a dynamometer. Water 
speeds in the 24-inch tunnel up to 35 knots are available. 
Vacuum pumps lower the air pressure above the water in the test 
chamber of the tunnel, in order to create an absolute pressure on the 
model propeller corresponding to the combined effect of atmospheric 
and water pressure on the propeller of the full-sized ship. Under these 
conditions, the phenomena of cavitation occur on the model propeller 
so that the test accurately represents the behavior of the full-scale 
propeller. Cavitation is the formation of water-vapor cavities, or 
“bubbles,” on the propeller blade surface, caused by high loading and 
consequent serious reduction of pressure on the back, or “suction side” 
of the propeller. Efficiency suffers when cavitation occurs. Cavita- 
tion effects are studied by means of stroboscopic illumination of the 
propeller being tested, and these effects are recorded by high-speed 
flash photographs, of 1/30,000-second exposure. 
In the laboratory building there are located two large machines for 
testing structural specimens, both full-size and model scale. One, the 
150,000-pound alternating-load testing machine, tests beams, columns, 
riveted and welded joints, and other structural members in alternate 
compression and tension over long periods of time, to discover the 
manner, loading, and number of cycles to failure in fatigue. 
The other large testing machine is a universal static-load testing 
machine with 600,000-pound capacity in either tension or compression. 
Stress-strain data, yield point, and ultimate strength of a wide variety 
of structural specimens may be obtained with this apparatus. 
One of the most unusual and recently completed facilities is the test 
pond for underwater explosion tests. This is a pentagonal pond, dug 
partly out of the solid rock and partly formed by built-up rock em- 
bankments. It is roughly 150 feet across and will carry water to a 
