Ventilation and Cavitation
In this part two issue of our Blog 3b, We are going to focus on the terms ventilation and cavitation that are often incorrectly used interchangeably. Although there are certainly similarities, and in some circumstances, they can be related yet technically, different phenomena.
Next is Cavitation:
Cavitation, on the other hand, is a bit more specific and technically can be more difficult to explain. Cavitation could be defined as the “phenomenon of the formation, rapid collapse, and subsequent implosion of vapor bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure”. As these bubbles collapse, energy is released in the form of a minute explosion that can cause minute damage to the surface of the material. In this case, the flow of water is caused by the propeller's rotational and forward movement through the water, while the surface in question is the blade surface of the propeller, itself. When these microscopic explosions occur, the surface metal can be eroded, and small pock marks can appear, causing "cavitation burns." The damaged area will appear to have been sandblasted at very close range on a stainless propeller and/or paint removed from an aluminum propeller.The cause of cavitation can arise from several factors, but it seems to occur most often, because of propeller blade leading edge imperfections, such as, nicks, dings, scratches, bends, impacts, etc. It can, also, be caused by improper propeller geometry, or upstream imperfections related to the hull, such as, hull design/configuration, hull imperfection, incorrectly installed accessories/appendages, etc. Basically, this is what we like to refer to a “dirty or disturbed water flow” and since there are so many possible causes, diagnosing the problem should really be done on a case per case basis. And one last thing, the incorrect style of propeller, not designed for your boat/motor setup is another factor. Hope this has helped clear up some questions and have a grrreat time on the water. The Proptologist