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Old 05-08-2013
bobperry bobperry is offline
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Re: Encapsulated Keel?

Alex:
It's a long story.
But there was a time, you were probably a kid, when designers had this idea that for a keel to be efficient it had to have "eliptical loading".

Say that twice, eliptical loading. Good.

This meant that the loads on the foils ( and I probably have this a bit off) had to describe in a vertical plane an eliptical curve. I could draw it for you.

The idea was that the drag of the keel would dissipate towards the tip reducing the tip vortex ad it's accompanying loads.

This "eliptical loading" gave way to keels with plan forms that features curved leading and trailing edges. Sort of an eliptical shape to the planform. But this really had nothing to do with eliptical loading. You could achieve eliptical loading with a highly tapered keel with straight leading and traling edges. Eliptical edges were of a red herring. But people bought into it anyway and the weird thing is that it did have some benefits apart from eliptical loading. If you reduced the root foil you could reduce the interference drag of the keel, i.e. where the fin meets the hull. Keep in mind that the perfect keel was not attached to the boat.!!!!!!

Short story is we had a series of keels with that highly taered shape. I used it myslef on the Nordic boats. It made sense. But it did put the VCG pretty high up on the fin. But the damn boats sailed really well.

Now we know better. It's better to get the VCG of the keel as low as possible, make the bat stand up and take advantage of the sail plan.

Phases and trends:
Yes, we went through quite a few. Some worked to some degree and some were bogus. But in the end we learned ( some of us) a little bit more about what makes a boat go.

Does that make any sense?

I have to go now. I'm certain there is someone I need to be rude to.
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