246 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
charge of the entire work of preparing the facilities for operation, 
is technical director and head of the technical division; and Capt. 
W. C. Mehaffey, U.S. N. R., is executive officer and production officer. 
The heart of the organization and the reason for its existence 
rest in the technical division. This division is divided further into 
three main divisions: hydromechanics, structural mechanics, and 
aeromechanics. 
Each of these divisions is headed by a senior officer, with officer 
assistants, specially trained and qualified for this particular work. 
The civil technical staff is of the same high caliber, the nucleus of this 
staff possessing a national and international reputation in this highly 
specialized work. 
In the hydromechanics division the principal work falls within the 
field of ships’ lines, propellers, and underwater forms such as mine- 
sweeping gear and torpedoes. After the technical design of a device 
is completed, a model is built to scale, in order to carry out the test 
necessary to check the form and to determine the power needed to 
propel or tow it; the test is made in one of the various model basins. 
The procedure in a typical test of a ship is as follows. 
The usual ship model is about 20 feet long, hollow, and fashioned 
from layers of wood glued together. It is carefully shaped to represent 
the outer surface of the ship’s hull, to exact scale, from keel to deck. 
The model is complete as to its underwater form, with rudder, propel- 
- lers, shafts, struts, bilge and docking keels, but without upper works. 
The model is first towed, non-self-propelled, over one of the main 
basins by the carriage which has already been described. 
In making a towing run the carriage starts from rest, and smoothly 
and gradually acquires the speed necessary for the test. When the 
carriage is towing the model at a uniform rate at the desired speed, 
and the model is producing its characteristic wave formation, the 
actual resistance of the ship model in pounds and hundredths of a 
pound is measured. 
Later a second, self-propelled test is run, in which the model is 
driven under its own power along the basin with small model propel- 
lers. Small electric motors installed in the model, one motor to each 
shaft, operate the propellers. An operator on the towing carriage to 
which the model is attached regulates the speed of the model ship. 
From the tests so made, calculations give the corresponding results for 
the full-sized vessel. 
Under the hydromechanics division is also carried out the design of 
propellers in connection with the Bureau of Ships, and the testing of 
model propellers based upon these designs. These model tests are 
made in one of the two propeller tunnels already described. 
