A ship's propeller generates thrust by rotating its blades, which displace water. This displacement creates a void, causing water to rush in and fill the space. This movement results in a pressure difference. Water accelerates from the front of the propeller blades to the back, forming a column of water slightly larger than the propeller itself. The increased velocity creates a water jet behind the propeller. This jet adds momentum and thrust to the water, propelling the vessel forward.

Cavitation occurs when the local pressure in the liquid drops below the saturated vapor pressure of water, leading to the formation of vapor bubbles. When producing thrust:

1. The propeller creates areas of high and low pressure due to the pressure differential on the blades.
2. If the pressure in the low-pressure areas (typically on the suction side of the blades) falls below the vapor pressure, vapor bubbles form.
3. These bubbles collapse violently when they move into high-pressure regions, producing shockwaves and leading to cavitation. This phenomenon is exacerbated by sudden variations in local pressure caused by blade movement.

Vortex cavitation originates from the vortices shed at the propeller blade tips and edges due to low-pressure regions.

• It occurs when there is a high angle of incidence between the water flow direction and the blade's leading edge.
• The low pressure within these vortices causes vapor bubble formation.
• This type of cavitation is heavily influenced by the vessel's wake field and the propeller’s design, especially the blade tip geometry.

Cavitation causes erosion of propeller blades through a progressive damage process. The high-pressure shockwaves created by the collapsing bubbles erode the blade surface material. This process is a type of mechanical corrosion. Initially, the damage may be minor pitting. However, as the process continues, the pits grow larger and deeper, leading to significant material loss and potentially structural weakening of the blade. The erosion is progressive, with small defects growing over time. This necessitates regular inspections and potential repairs or replacements to prevent failure.