Prevention of cavitation corrosion

Abstract

The present invention directly deals with the problem of cavitation corrosion by modifying the hub of a propeller to eliminate low pressure areas. The present invention is the placement, formation, and/or insertion, on a propeller, of a non-smooth area in each facet of the hub between each of the blades. This area is also sometimes referred to as the “blade root”. The exact configuration of the raised area can vary from a longitudinal raised area to single or multiple bumps or buttons to single or multiple pointed projections. By modifying the hub, whether by casting a new propeller with a redesigned hub, or by retrofitting an existing hub, the elimination of corrosion occurs when a high Developed Area Ratio (DAR) propeller hub has one or more raised protrusions on the surfaces of the propeller hub between each blade seat. The addition of the raised protrusions discourages the formation of low pressure areas around the hub. By removing the low pressure areas from the immediate area around the hub, the shock waves caused by the collapse of the low pressure areas is moved away from the propeller, thus eliminating corrosion impact damage.

1 . A propulsion apparatus for propelling an object through a fluid, said apparatus comprising: 
 a hub;    a plurality of blades connected to said hub, each of said plurality of blades connected to said hub at a blade root; and    disruption means integrated into each blade root, said disruption means altering the flow of said fluid over said hub thereby reducing areas of low pressure around said hub.    
   
   
       2 . The apparatus of  claim 1 , wherein said disruption means are integrated into each blade root by one of the following techniques: casting, machining, and retro-fitting.  
   
   
       3 . The apparatus of  claim 2 , wherein said disruption means comprise one or more raised nubs.  
   
   
       4 . The apparatus of  claim 3 , wherein said one or more raised nubs are of variable height.  
   
   
       5 . The apparatus of  claim 2 , wherein said disruption means comprise at least one of a raised linear ridge, a series of raised linear ridges, screws, threaded bullets, angled protrusions and crescent shaped depressions.  
   
   
       6 . A method of disrupting fluid flow around a hub of a propeller so as to minimize cavitation damage to said propeller, the method including the step of integrating disruption means into said propeller so as to alter the flow of said fluid around said hub.  
   
   
       7 . The method of  claim 6 , wherein said propeller comprises: 
 a hub; and    a plurality of blades connected to said hub, each of said plurality of blades connected to said hub at a blade root.    
   
   
       8 . The method of  claim 7 , wherein said step of integrating disruption means into said propeller comprises integrating said disruption means into each blade root.  
   
   
       9 . The method of  claim 8 , wherein said disruption means are integrated into each blade root by one of the following techniques: casting, machining, and retrofitting.  
   
   
       10 . The method of  claim 9 , wherein said disruption means comprise one or more raised nubs.  
   
   
       11 . The method of  claim 10 , wherein said one or more raised nubs are of variable height.  
   
   
       12 . The method of  claim 9 , wherein said disruption means comprise at least one of a raised linear ridge, a series of raised linear ridges, screws, threaded bullets, angled protrusions and crescent shaped depressions.  
   
   
       13 . A method of modifying a hub of a propeller to minimize cavitation damage to said propeller, the method including the step of adding disruption means to said propeller, said disruption means integrated into said propeller so as to alter the flow of said fluid around said hub.  
   
   
       14 . The method of  claim 13 , wherein said propeller comprises: 
 a hub; and    a plurality of blades connected to said hub, each of said plurality of blades connected to said hub at a blade root.    
   
   
       15 . The method of  claim 14 , wherein said step of adding disruption means into said propeller comprises integrating said disruption means into each blade root.  
   
   
       16 . The method of  claim 15 , wherein said disruption means are integrated into each blade root by one of the following techniques: casting, machining, and retro-fitting.  
   
   
       17 . The method of  claim 16 , wherein said disruption means comprise one or more raised nubs.  
   
   
       18 . The method of  claim 17 , wherein said one or more raised nubs are of variable height.  
   
   
       19 . The method of  claim 16 , wherein said disruption means comprise at least one of a raised linear ridge, a series of raised linear ridges, screws, threaded bullets, angled protrusions and crescent shaped depressions.