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Snatch Block

Bubbles Off Of The Keel

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What would cause a stream or line of bubbles coming off the keel?

Heeling may even make it worse.

Bulb/torpedo keel is what's below.

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Prankster 

625B3394-7FE2-494C-8FBB-65DD679BDE67.thumb.jpeg.15ad5539d0e82262ff9e05995cdcb603.jpeg

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Sounds like keel tip vortices.  Every keel creates them when generating lift.  Bulbs create their own set of vortices as well.  Probably not the best illustrations, but you should get the idea.  Tip vortices become more pronounced the more a boat heels.

Vortex.jpg

bulb_streamlines_Large.jpg

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6 minutes ago, 12 metre said:

Sounds like keel tip vortex.  Every keel creates them when generating lift.  Bulbs too.  Probably not the best illustrations, but you should get the idea.

Vortex.jpg

bulb_streamlines_Large.jpg

that would not explain generation of bubbles unless you're doing mach 10

I think the question is - where are they coming from ?

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3 minutes ago, duncan (the other one) said:

that would not explain generation of bubbles unless you're doing mach 10

I think the question is - where are they coming from ?

I was thinking the OP mis- described them as bubbles.  More of a foamy churn.

If they truly are bubbles, then I have no idea.

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Vortices are pretty large energy sucks.  Once formed, they tend to pretty much spin "forever".  

Lots of efforts have been made to diminish them.  Bulbs on the bottoms of fins help as an endplate, but if there are any hollows or unfair surfaces on the fin or the bulb, those can create a separated flow and generate bubbles.  And make you slow.  Even a faired surface will generate a vortex from flow from high to low pressure sides starting the rotation.  

The Peterson keels were particularly terrible at creating vortices if I correctly remember the naval architects comments on the crew from back then.  

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Does the keel have a kelp cutter?  If so could it be drawing air down the slot?

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All lift creates one big vortex loop. No vortex no lift...

I like the kelpcutter hypothesis. If it really is bubbles.

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30 minutes ago, fastyacht said:

All lift creates one big vortex loop. No vortex no lift...

I like the kelpcutter hypothesis. If it really is bubbles.

Exactly, vortex is required.

Vapor bubbles can form at discontinuities. For example a fat flat trailing edge, or a sloppy thru hull. Doesn’t take much speed. But they normally disappear quickly. Maybe not in certain gassy water chemistries?

Rudder posts and centerboard trunks can suck air. As can thru hulls open to the air, like galley drains.

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2 hours ago, Left Shift said:

The Peterson keels were particularly terrible at creating vortices if I correctly remember the naval architects comments on the crew from back then.  

Lefty, would you mind rephrasing that sentence, as it sounds like the crew was disparaging a Peterson keel.

If so, did "the crew" know what they were talking about?

 

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2 hours ago, Fiji Bitter said:

Lefty, would you mind rephrasing that sentence, as it sounds like the crew was disparaging a Peterson keel.

If so, did "the crew" know what they were talking about?

 

Agreed.  If the Peterson trapezoidal keel was so bad then why was upwind ability a hallmark of Peterson`s IOR designs.

I think Farr said something years ago to the effect that you don`t need an elliptical planform - you need an elliptical lift distribution.

And a trapezoidal keel generates a nearly elliptical lift distribution.  Not exactly, but pretty close and much easier to fabricate than a ``mickey mouse ear`` keel.

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11 hours ago, Snatch Block said:

What would cause a stream or line of bubbles coming off the keel?

Heeling may even make it worse.

Bulb/torpedo keel is what's below.

You're sinking.

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6 hours ago, 12 metre said:

Agreed.  If the Peterson trapezoidal keel was so bad then why was upwind ability a hallmark of Peterson`s IOR designs.

I think Farr said something years ago to the effect that you don`t need an elliptical planform - you need an elliptical lift distribution.

And a trapezoidal keel generates a nearly elliptical lift distribution.  Not exactly, but pretty close and much easier to fabricate than a ``mickey mouse ear`` keel.

As it turns out, Eliptical distribution is not actually optimum when you conider the whole picture ofstructural weight. Prandtl wrote a paper in the early 30s that went beyond the "Lifting Line" theory he wrote in the early 20s. And Horten independently discovdered the same thing. The optimum considering structural weight is termed the "bell-shaped" distribution.

https://ntrs.nasa.gov/search.jsp?R=20160003578

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2 minutes ago, Grande Mastere Dreade said:

 

what are you thinking  ?  

I'm sinking!

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Just now, Hitchhiker said:

Sounds like 4th mode problems too me.

 

What about the 5th mode.  It could be fifth mode you know, Mr. smarty pants.

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And here I thought this was about the catamaran keel (s) with Giggles and Gomer.

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Somebody used the head and didn't close off the seacock.

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Im curious as to what your proof is that there are bubbles coming off the keel while youre underway. You have a gopro down there?

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3 hours ago, Mark Set said:

Im curious as to what your proof is that there are bubbles coming off the keel while youre underway. You have a gopro down there?

The coolest "bubbles" I've ever seen are the phosphorescent vortex trails coming off the keel tip vortex at night.

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