Analysis and mitigation of mechanical shock effects on high speed planing boats

Abstract

United States Special Forces use high-speed planing boats in the performance of their missions. Operation of these boats, particularly in rough seas, exposes the occupants to severe mechanical shock exposure that has been linked to significant increase in the rates of acute and chronic injury. While many government and civilian organizations have researched various aspects of this problem over the past decade or more, no effective solution has yet been implemented in the fleet. In response to this problem, the Commander Naval Special Warfare Command in San Diego, CA forwarded a request to MIT's Ocean Engineering Department calling for a study of the problem. The object of this thesis is to conduct a comprehensive analysis of the problem, to research methods by which the problem can be mitigated, and to develop and validate a method for laboratory design, test, and evaluation, of shock mitigation systems. First, a theoretical and empirical study is conducted of the hydrodynamic interaction between a boat's hull and the seaway, and how this interaction results in the generation of mechanical shock. Actual acceleration data is obtained from the boats while underway in typical operating conditions, and other similar data is obtained from previous studies. Second, the mechanisms by which exposure to mechanical shock and vibration causes acute and chronic injury are investigated. Past human and animal testing is reviewed, along with information on the transmissibility and mechanical impedance of the human body. Information of this type, along with other injury data compilation studies, have contributed to existing injury prediction. Third, a study and is made of the methods by which mechanical shock exposure on high-speed boats can be mitigated. Interfaces (e.g.- hull-seaway) are identified where shock mitigation can be achieved, and existing or conceptual shock mitigation systems are discussed. Additionally, operational methods (such as training) of reducing shock exposure effects are discussed. Finally, a laboratory drop table apparatus is fabricated for use in the design, test and evaluation of shock mitigation systems. This test apparatus is validated by successful reproduction of shock events such as those experienced on high-speed boats, as well as by excellent repeatability and controllability.