The Experimental Naval Tank
When it was proposed to build the West Engineering Building Dean Cooley incorporated into the plans provision for a naval testing tank. His justification for this was that the United States Navy Tank at Washington was occupied with naval work and hence was unavailable for merchant ship experimental research. Moreover, the development of shipping on the Great Lakes afforded an opportunity for direct contributions by the University to ship design. A subflume in the bottom of the tank was to be connected to the Hydraulic Laboratory, providing ample water supply for the testing of pumps and water wheels, and lastly the tank-room galleries were to be utilized for research in the transmission of compressed air through long pipelines.
During construction of the West Engineering Building, which was completed in 1904, the Naval Tank was extended 100 feet outside the main building to a length of 300 feet. In a few years, however, an addition to the building permitted construction of an additional sixty feet, which at the time was not flooded and put to use because of prior demands for floor space. This tank area was decked over with temporary planking, thus providing two rooms for the use of the Department of Electrical Engineering.
The bottom of the Naval Tank, which is semielliptical in cross section, is twenty-two feet wide and nine and a half feet deep, with a wetted area of about 185 square feet. A three- by four-foot flume extends the length of the Tank below the normal bottom.
All apparatus was designed by Dean Sadler and, with the exception of the towing car, was built in the University Shops. The car was furnished by the Russell Wheel and Foundry Company, of Detroit, in 1904, and its towing speed limit is about 480 feet per minute in low gear and 840 feet per minute in high gear.
Until 1936 practically all models were made of paraffin and were cast roughly to form in a clay bed. The waterlines were then cut on a pantograph-controlled twin rotary cutter machine, the final form being hand finished. The advantages of this technique were economy, ease of making alterations, the possibility of using the same material repeatedly, and the fact that the parent set of lines could be employed to produce a family of models for research purposes.
The disadvantages were sagging or hogging, owing to high temperatures, and alteration in frictional resistance, due to weathering of the wax surface. As the Tank work gradually changed to projects having single models, it was decided in 1936 to standardize by using Page 1283wood models. These are glued together from seven-eighths-inch white pine lifts cut to shape on the band saw and finished by hand to transverse templates.
Improvements in technique and apparatus have been made as required, but when funds are available a more modern dynamometer and car will be installed. The University of Michigan Tank has been in great demand in the development of barges and towboats to operate on the Mississippi and Ohio rivers because of its 140-foot false bottom, which can be adjusted in depth to simulate shoal water conditions. The Tank has been used in a study of the correction of yaw, a condition prevalent in barge towing, and much attention has been given to the improvement in speed and fuel economy of existing lake bulk carriers. This work has been under the direction of Baier.
Sensing the need for closer co-operation and standardization of technique among the various tanks, Baier organized in 1938 the American Towing Tank Conference (ATTC). The first meeting was held at the Stevens Institute of Technology, Hoboken, in April, 1938.
Although open-water research has been carried out on propellers and paddle wheels, self-propelled model tests have never been undertaken by the University. It is believed that this type of work should be restricted to models of at least twenty feet in length in order to avoid scale effect, and these sizes are beyond the present Tank's capacity.
Among the research problems undertaken have been the following. Series 1050 was tested in 1921 for the Fairbanks-Morse Company to find the best forms for fireboats. A fireboat is usually made as short as possible to enable it to maneuver readily in docks, and usually it has a high speed relative to its length. The forms were designed by Alfred J. C. Robertson, and the series consisted of four models all cut from the same waterlines. This series was unique in having the vertical spacing changed. The results obtained were very satisfactory throughout the speed-length ratio for which they were designed.
The first tests in the 1130 series were undertaken at the request of the United States Shipping Board in 1919. Nine preliminary forms were tested, and form 1130 was selected. Nineteen models were made from a set of parent lines and tested with varying percentages of entrance and run. This series was planned by Robertson.
At the University of Michigan four more models with a 50 per cent run were tested in order to complete the series. This was as far as it was originally intended to go with tests on this model, but the question arose concerning the effect of section shape upon resistance, and it seemed best to use model 1130 for such experiments. A medium shape was used on the twenty-three models previously tested, and variations were made in both directions. The tests seemed to indicate that a 27 per cent entrance and a 40½ per cent run were about the best proportions for general purposes.
All the tests had been made for a 425 by 56 foot ship. The next logical variation seemed to be in the beam. Kent's paper in 1919 on the "Effect of Variation in Beam" had covered a wide range, there being 13-foot intervals between the beams of the successive ships tried. It seemed advisable to cover a more limited range and to have about 4-foot intervals. Thirty models were used to cover this ground, and each model was tested at four different drafts. The experiments upon shape of section having shown that for this type of model best results were obtained with V-shaped forward sections and bulbous-shaped stern sections, these thirty models were tested with V-shaped sections forward and bulbous-shaped sections aft. Thirty-six models were used to Page 1284investigate the effect of rise of floor; eighteen models were tested with an entrance of 33.93 per cent and eighteen with an entrance of 40.7 per cent.
In the 2030 series, during the summer of 1920 the Emergency Fleet Corporation authorized the test of eighteen models of fairly fine form, varying from a prismatic coefficient of .53 to a prismatic coefficient of .76, with parallel middle body varying from o per cent to 35 per cent.
Series 2057 was tested in 1929 for the United States Shipping Board. The forms were designed under Admiral Taylor's direction and were for a form of about .66 block coefficient. The parent lines were very close to Baker's 56-C, although the models were made with some rise of floor.
The models represented 400-foot ships, but with breadth and draft varying to give ship forms ranging from L — 400', beam — 30.94', draft — 13.75', to L — 400', beam — 76.5', draft — 27.82'. Fifteen different models were necessary. The requirements of the Shipping Board would have been met if each of these fifteen models had been tested at one draft only, but it seemed desirable to test the models at a draft of .8 and also at 1.2 of that called for by the Shipping Board. The results were reported by James Lee Ackerson in the Transactions of the Society of Naval Architects and Marine Engineers for 1930 under the title "Test Results of a Series of Fifteen Models."
In 1935-36 a series of seventeen barge forms was tested for the Dravo Corporation of Pittsburgh, Pennsylvania. The tests consisted of fitting ends of different shapes to a middle body and of testing the models at three different drafts in shallow water corresponding to twelve feet for the full-sized barge. As a result of these tests a final form was obtained which could be driven with 30 to 33 per cent less power.
Three similar models were tested in the Tank, and the data were worked over assiduously, but no frictional coefficient could be obtained. The data obtained in testing these models were published in 1932 as a part of the discussion in Commander Saunders' paper "Tests of Geometrically-Similar Ship Models," Transactions of the Society of Naval Architects and Marine Engineers.
From 1915 to 1921 about fifteen different submarine forms were tested for the Electric Boat Company of Bridgeport, Connecticut.
In October, 1929, two models of Crane's design of the cup defender, "Weetamoe" were tested in the Naval Tank. These models were run upright and also in two inclined positions. As a result of these investigations the longer, narrower model was chosen.
In 1931 numerous tests were made for Burgess upon certain of his yacht forms, such as the "Valiant" and "Avatar." Changes were made in the shape of the longitudinal profile and in the shape of the section. The various forms were pushed down the tank at an angle to the direction of motion to determine the center of lateral resistance.
Various tests have been made from time to time upon V-bottom and round-bottom forms of high-speed boats. Certain patented Hydro-Curve forms have been tested for the inventor. The Fairbanks-Morse series deals with forms used in small fishing, trawler, and other commercial vessels.
In 1929-30 a series of tests supplementing those carried out some years previously by the Washington Tank was made for the Shipping Board upon types of bulbous bows. Results of these tests were published in the 1930 Transactions of the Society of Naval Architects and Marine Engineers under the title "Results of Experiments upon Bulbous Bows."
Page 1285From time to time various fireboat forms have been tested, and the results assembled and correlated by the students as a class project.
Because of the practical gains in speed and economy accomplished by model tests for the Dravo Corporation, continued research has been carried on relative to the most efficient arrangement of barge flotillas. This work proved so successful that river transportation, particularly upstream, has benefited.
An extensive program of tank tests for the Army Transportation Corps on the effect of shoal and restricted water on the speed and resistance of barges and flotillas has been under way during 1950-52. The results are intended to guide government plans for widening and deepening the principal inland waterways for navigation purposes.
In 1947 the new addition to the East Engineering Building was completed, permitting the Department of Electrical Engineering to release the space it had occupied in the West Engineering Building. This space was used for the completion of the north end of the Naval Tank, which was lengthened some sixty feet and fitted with a wave dampening beach. New rails were installed and a false bottom for shoal water work was built. Plans are under way to renew bearings and car wheels, completion of which will modernize the tank.