Rethinking the Winged Keel

So a while back I picked up the Horan/Lexcen Winged Keel aka Star Fin and I’ve been hooked ever since. Recently I broke one of the wings off while duck diving on a rock reef. Lately I’ve been thinking about the way it performs and the draw backs that has. So I took the original design and came up with a new concept while staying true to the original idea of producing lift and drive. First I noticed that the original fin tended to hesitate at times while being maneuvered. My conclusion was that the wings which are flat needed to be curved to allow the board to roll on its rail easier. Next I took some area out of the base at the trailing edge to loosen it up. Lastly I thought that I can foil the wings thin so they have flex and act like a bird’s wing. Before I attempt to make the fin I wanted to get people’s opinion if it’s a logical idea. I’m open to everyone’s criticism and input. Below is a mock up I made out of cardboard. The base is 5" and 6.5" from the base to the wings. The wings are 3" base and 3.5" long. Thanks.

If you want it to roll to rail easier, I think the curvature should be convex down, not up.

Its quite a complex issue, I’d be prepared to make one, test it, make another, etc, and so on, for about 10-12 fins if you want to come up with something better.

If I were to make a stab at it, I’d rake the ellipse, and shrink the wings down, extent them rearward a little, and basically keep the angles already used ie: kill induced drag, minimize vertical lift from a fin.

I say, ‘GO FOR IT !!’

Mikey, what will you make it out of …wood core ? solid glass ? foam core ?

And how do you attach the wings ?

I’ve toyed with the idea of having a go out of foam core…only the idea, so far…

So, please let me know how you, and it goes, I’m interested !

cheers !

   ben

Absolutely go for it.

When I made about a dozen templates last summer, I was quite impressed at the necessity for stiffness in a fin. Fins made of softer materials flexed in the water, and felt mushy under my feet. My rule of thumb was that if I can flex it in my hands, it is too soft.

I don’t know how stiff these wood or foam core fins end up. Presumably you can make them stiff enough. Just another $0.02 for things to watch out for. A perfectly rigid fin lets you study the impact of the fin shape. If it flexes, there is another variable. And, if a flex fin works well in head high waves, it will not work well in double overhead, or under waist high - they are speed sensitive.

Don’t get discouraged if the first one doesn’t ride well…keep going, take notes, and it’ll come around.

Thanks for the response Blakestah & Chipfish61. I first had the idea to make the convex down but I really want as much lift from this fin as possible. The board that it will be used on has a really thin tail which tends to sink when doing cutbacks. I agree that the wings should be a little smaller. I’m planning on making the vertical body out of 6oz. and the wings out of 4oz. The fiberglass for the wings would be laid up on a curved block so the curve in the wings would come close to what I want. After I foil the body and wing, I’ll attach the two with glass or maybe even fin rope. I wont start on the project for an other two weeks or so which will give me time to toy around with the idea. Thanks.

Blakestah, I’ve never really liked flex fins but I thought by making the wings flex, they wont fight with the water flow when lend on rail. Which happened with the Star Fin making it hesitate.

Hey Mikey,

Your approach to construction will work fine But the fillets will interfere with performance. I don’t thinlk there’s a reason to use different weights of glass to stack the panels with. Another way to approach the project is to build the fin in two pieces and put them together with a seam right up the base. This will require making a jig to layup one side of the base and one wing. After the two pieces are layed up. You can join them buy putting several layers of glass between them after you sand the flat of the inside of each piece. Foiling can be done after the fin is built. You’ll have to fill the top of the arch with some glass and resin but that won’t be a big deal. You’ll be able to foil the fin completely assembled if you have a small high speed grinder and the patience to work the areas where the facets come together with a block and paper. The hardest part of the foil will be the concaved area of the wing.

Consider that as you add rake to the fin base you add drive and that the wing will dampen rail the rail exchange as you increase it. I feel that convex area on the bottom of one wing will be nulified by the concave area on the other one so you really don’t gain and facility in rail to rail exchange by arching the leading edge of the wing. The amount of lift the wing generates will also depend on how you foil it.

I’ve made a Mod~Starfin and amy waiting to hear from Cheyne to see what he thinks. 'Till then mine’s under wraps.

Good luck on your project.

Mahalo, Rich