Parallel fins

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Brig North
Posts:26
Joined:22 May 2005, 04:35
Parallel fins

Post by Brig North » 05 Feb 2007, 00:00

I know nothing of boat design, but I was curious why parallel keel fins are preferred (with the exception of Bantock's double taper design) over nearly any other design? Is there a performance advantage to be gained, ie ability to make the fin narrower (6% fins seem to be the rage)?

Thanks.

Brig North

Steve Landeau
Posts:256
Joined:26 Nov 2003, 07:25
Location:USA 12

Post by Steve Landeau » 05 Feb 2007, 04:27

My opinion.... they're simly easier to manufacture, and there's not enough difference in performance between the types to mess with the hassle. if one was absolutely better than the other, the slower ones would become obsolete, and that's not happening. There are many good fins of various shapes and sizes out there doing the job. The scientific numbers would say that a double tapered fin would have less drag, but actual race results do not seem to make one faster than the other. My limited testing has shown that the airfoil shape is much more important than whether it's tapered or not.
Steve Landeau
AMYA 10859
IOM USA 112
Finn USA 112
Cal 25 #548

Lester
Posts:611
Joined:14 Oct 2004, 22:29
Location:GBR 105
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Post by Lester » 05 Feb 2007, 07:33

Steve Landeau wrote:The scientific numbers would say that a double tapered fin would have less drag, but actual race results do not seem to make one faster than the other
In theory, the tapered fin should show slightly less drag because it sheds a slightly smaller vortex at the tip. Perhaps the bulb makes a sufficient end plate to a parallel fin so that the difference in tip vorticity no longer makes a practical difference.
Lester Gilbert
http://www.onemetre.net/

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