When a propeller turns its blades, they expel the water backwards, leaving a vacuum that is immediately occupied by new liquid molecules. If the turning speed exceeds certain limits, the ejected water carries such force that it prevents the vacuum formed from being occupied by other water molecules.

This phenomenon is called cavitation, which manifests itself in an increase of the number of revolutions (vacuum turning) noises, vibrations and foam formation in the stern. The phenomenon of cavitation is directly related to the depression that is created on the anterior face of the propeller blades.

The blades of a propeller spinning at high speed create such a depression on its front face that the water boils at room temperature; the bubbles that come out of the propeller are not air, but strictly water vapor. These bubbles move quickly backwards, until they find an area of greater pressure where they will become water again imploding (the opposite of exploding) against the propeller blades themselves and starting a microscopic metal particle in each collision.

The origin of the bubbles is at the leading edge of the propeller, but the damage is manifested in the back with the appearance of a corrosion, which goes back in its destructive process to the center of the blade.

Cavitation manifests with greater intensity the faster the ship is, the faster the propellers turn. It is avoided by reducing engine revolutions and gradually increasing them. Cavitation also decreases engine performance.

This brings with it noises and vibrations that cause damage to the propeller, which will lead to loss of performance, causing the propulsion system pieces to lose useful life, and increase the maintenance costs of the ship.

These vibrations produced by propellers are very damaging, being one of the areas of the ship in which the amplitude of the vibration becomes several times greater than those of the central areas (machines).

The vibrations caused by propellers have their origin in these principles:

1. The effects of the blades on the water: the influence of the water displaced by the propeller will affect the hull of the ship in proportion to the amount of blades and revolutions.
2. The inequality of forces on the core of the propeller: if the blades are misaligned with respect to the mass whether their height between blades is wrong or their spacing between blades is not adequate.