Analysis of factors affecting the sound generated by airboats

This study presents an experimental and analytical investigation of the factors that affect the sound generated by airboats as well as the interaction among these factors; an airboat travels on water and wet land by means of an air pusher propeller attached to an internal combustion engine. These analyses show that the engine and propeller RPM are the main contributors of sound. The contribution of the engine is a tonal sound that is reduced by using a muffler. The sound generated by the propeller is a flapping sound clearly identified at high revolutions (over 1800 RPM). Above mid-range speeds, the propeller sound takes over, and any reduction of sound on the muffler does not play any role. The only method to control the sound of an airboat without any design modifications is to maintain the operational RPM at mid-range when the muffler's devices contribute to the sound reduction.