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Interesting Wing Cavitation


Mastercrafter
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Noticed this on my last ski, and it’s starting on my new ski already. There’s a line under the leading edge of the wing that appears to be from cavitation. First through the anodizing, and it’s actually pitting the aluminum.  
 

This means a negative pressure behind the front edge of the wing is is allowing the water to boil and become a gas, create a bubble, and then when the bubble collapses, it creates a shockwave that is actually “damaging” the fin. 
 

There’s even more going on with our fins than I thought. Just thought this was interesting. Because I am who I am, I’m now going to machine out the old fin where the cavitation is happening and see if it makes any difference in the ride. 
 

.. or is it from the hole in the fin? 

 

IMG_7919.jpegIMG_7920.jpegIMG_7923.jpegIMG_7922.jpeg

 

 

Edited by Mastercrafter
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@Mastercrafter

Its not from the wing specifically. It derives primarily from the hole geometry, however the wing has the ability to further decrease the pressure in that area and increase the propensity of cavitation under the wing.  

I've seen lots of fins with cavitation pitting on all 5 holes, but typically the most noticeable under the wing.

You can run a slot under the wing for sure.  Have done that many times.  Ski will likely feel much more stable off the second wake.

 

Edited by adamhcaldwell
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Pressure areas are formed as the water accelerates around and moves past the prop. As the prop moves faster, it creates a lower pressure around it. As it reaches vapor pressure, the water vaporizes and forms small bubbles of gas.

When the bubbles collapse, they typically cause very strong local shockwaves in the water, which may be audible and may even damage the blades.   

SAME AS ON PROPELLERS.....from boat forum

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14 minutes ago, liquid d said:

Pressure areas are formed as the water accelerates around and moves past the prop. As the prop moves faster, it creates a lower pressure around it. As it reaches vapor pressure, the water vaporizes and forms small bubbles of gas.

When the bubbles collapse, they typically cause very strong local shockwaves in the water, which may be audible and may even damage the blades.   

SAME AS ON PROPELLERS.....from boat forum

Yup. A ding in a prop can ruin both gelcoat and the rudder. 

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17 minutes ago, adamhcaldwell said:

@Mastercrafter

Its not from the wing specifically. It derives primarily from the hole geometry, however the wing has the ability to further decrease the pressure in that area and increase the propensity of cavitation under the wing.  

I've seen lots of fins with cavitation pitting on all 5 holes, but typically the most noticeable under the wing.

You can run a slot under the wing for sure.  Have done that many times.  Ski will likely feel much more stable off the second wake.

 

 Was hoping the scientist might chime in. Thanks. Well now I have no choice but to a slot a fin and see how it feels. Are there downsides? How wide and long should I start? 

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@Mastercrafter - I have a few fins that show similar wear.  Carbon fin examples are even more extreme and have more surface erosion.  Additional pressure / velocity differentials & vortices off the wing accentuate the cavitation.  Modeling the dynamics of a ski in water is very difficult, the many operating mediums make it a huge challenge.

@adamhcaldwell - very true.  

Edited by DW
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