---

I found this on boats.com and thought it was a short explanation between the two terms.

The terms are often used interchangeably and often incorrectly, let's look more closely at what they actually mean.

PROPELLER CAVITATION

Cavitation is the formation of air bubbles on the propeller. Cavitation usually occurs as a result of prop damage and you'll feel it in the form of vibrations. The damage makes the water boil due to improper pressures between the back and the front of the blades.

Cavitation is bad for three reasons. First it can physically damage the propeller with pits or burns usually at the top of the blades. Secondly, it causes those vibrations which makes your ride less comfortable. Thirdly it reduces bite, which reduces efficiency.

PROPELLER VENTILATION

Ventilation, on the other hand, is the propeller sucking in air. This may happen because you have the engine trimmed up too high. It can occur because you're jumping waves and the back of the boat is actually coming up near the surface of the water, or perhaps you have a really sharp turn and as the boat leans your propeller is too close to the surface. Ventilation can also occur from improper mounting of transducers, drains, thru-hull fittings, etc. Condition of the hull can be a factor such as damage, marine growth, bottom condition. This is usually in the last 5ft before the propeller. Damage to the lower unit in front of the propeller can cause it too. Basically any disturbance that would effect the flow to the propeller.

Ventilation is also bad mostly because it can cause a radical reduction in thrust and also it can cause your engine to over-rev.

CAVITATION AND VENTILATION HOW CAN YOU TELL THE DIFFERENCE?

If you can feel vibration and your propeller has visible pitting, you have cavitation and you probably need professional help. If, however, your engine is over-revving you have a ventilation issue and this is usually something you can fix yourself.