Please use this identifier to cite or link to this item: https://hdl.handle.net/11681/21280
Title: Model study of pontons and pneumatic floats
Authors: United States. Mississippi River Commission.
U.S. Army Engineer Waterways Experiment Station.
Keywords: Pontons
Pneumatic floats
High-velocity flow
Publisher: U.S. Army Engineer Waterways Experiment Station.
Engineer Research and Development Center (U.S.)
Description: Technical memorandum
Synopsis: This memorandum constitutes a comprehensive report on the results of a model study performed-at the U. S. Waterways Experiment Station for the Engineer Board, Fort Belvoir, Virginia, on pontons and pneumatic floats used in the construction of floating military bridges. The purpose of the study was to (a) develop an attachment for the bow of the present 25-ton ponton; (b) determine the optimum bow shape of future pontons to be constructed; (c) study the most effective methods of anchorage; and (d) investigate the upstream bow shape of the pneumatic type float. The above alterations and investigations were desired with a view to increasing the freeboard of the present American 25-ton ponton and pneumatic float in high-velocity flow. All tests were conducted in a 4-ft wide flume with flow maintained at a depth equivalent to 20 ft in the prototype. The pontons were built to the linear-scale ratio, model to prototype, of 1 to 8. It was determined from the model study that the present American 25-ton ponton would not perform satisfactorily in high-velocity flow under conditions of heavy loading. As the ponton became submerged in high-velocity flow, the steep rake of bow prevented the use of the dynamic force of the stream as a lifting force, thus decreasing the freeboard at the bow. To improve the frceboard conditions of the present heavy pontons in use several types of attachments were developed that helped considerably. In order to increase freeboard, it was found that either of two things could be done; (a) the rake of the bow could be flattened, or (b) the height of the bow could be increased. No improvement in freeboard could be made by revising the method of anchoring the ponton. Additional tests on the development of an entirely new bow shape revealed almost the same information as the attachment tests but did serve to emphasize the fact that the shape of the bow in plan (stream-lining) had little effect in improving the amount of freeboard. Comparison of the German, 3ritish, and American 25-ton ponton of original and alternate design revealed that when loaded to the same freeboard on the side, the flat rake of the German bow makes it superior to the other types. The flat rake of the British ponton operates very well in providing freeboard but the extra bow height of the German and American pontons accounts for additional freeboard. The type Ml pneumatic float operated satisfactorily in high-velocity flow until the loading was such as to cause waves to break over the bow. As soon as this occurred the bow of the float would dive at frequent intervals, remaining beneath the surface for some time.
Rights: Approved for public release; distribution is unlimited.
URI: http://hdl.handle.net/11681/21280
Appears in Collections:Technical Memorandum

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