Pressure pulse (propeller)

Propeller pressure pulses are the fluctuating pressures the propeller imprints on the hull above it as each blade passes through the wake peak, the chief source of hull vibration and structure-borne noise. They have two parts: a non-cavitating component from blade thickness and loading, and a much larger cavitating component from the growth and collapse of the sheet cavity, which can dominate the first blade-rate harmonic. Amplitude is reported at blade-passing frequency f = Z n (blade number times rate of revolution) and its harmonics; classification guidance keeps the first-order pressure pulse on the order of a few kilopascals to protect aft accommodation. Tip clearance, hull-wake smoothing, skew, and unloaded blade tips are the main design levers for cutting them.