Measurement of spray-on damping effectiveness and application to bow thruster noise on ships

Two vessels of nearly identical design have been tested during operation of their bow thrusters. The primary difference between these vessels, for the purpose of this paper, is the application of a spray-on damping treatment in one vessel whereas the same areas are bare in the other. Damping treatment was applied to all bulkheads and overhead of the Bow Thruster Room; the side bulkheads in the Bow Thruster Room are tank partitions, not the side shell. Comparison of vibration measurements of vessel structure with and without damping indicate good effectiveness at reducing local vibrations. However, airborne noise levels on the Main Deck and above were not reduced. Reasons for this apparent discrepancy are explored.