Shaping Keels...

Thanks to a very generous Swaylockian donor, I’ve got a nice piece of cabinet-grade plywood and I’ve been drawing up keel templates all week. I did a lot of picking through the archives and found loads, and loads of shapes. I haven’t been copying templates… just looking for inspiration and drawing my own. Ironically, I’ve found drawing out fin curves harder than drawing board outlines!

What I haven’t found in the archives is much of a discussion on the benefits or drawbacks of different templates for a twin fish (there’s actually a good deal on different quad and twinzer setups)…

For instance… I saw plenty of higher-rake, lower base keels on chip’s post in the archives… what would a fin like that work like in comparison to a more classic lis template?

Also, should the decision to run the keels parallel or toed-in affect the fin template? I’ve read it should affect the foil, but I’m not sure about the template…

At any rate, I was curious and didn’t find this info in the archives. If I missed a thread, let me know :slight_smile:

It’s all one big experiment. I’ve been making these things for over 30 years now.

Here’s a distorted view on wood ply fins:

I find the more twin-like good for longer fish and I might toe them in a bit. The keel fins work quite well

if they are parallel although I’ve toed them in slightly as well, but some glide is lost for vert performance.

I guess overall it depends upon what your goal is with the board…

Have fun.

Wow. Those look great! Thanks for sharing the inspiring photos. For this fish I’ve been planning on running the fins parallel. My current fish has a bit of toe-in.

My goal behind this board is to get more hold on steep faces (I’m hoping the lower volume will help the backend bite into the wave a bit better)… and I was thinking that the slightly more parallel outline and parallel fins will give me back some speed lost from less volume. Does my thinking make sense?

Of the templates I’ve drawn, the one that’s the closest to a traditional lis template keeps catching my eye. It’s pretty safe… 9" base, 5" deep, with a lot of rake and a bit more cutout on the back edge than the ones you posted.

You talk about fin shape and toe in, but no mention of distance from tail & rail. Try adjusting back.

That’s a good point. The fish I ride now has keels set an inch forward of the buttcrack. I’ve seen a lot of mention of positioning them exactly even with the buttcrack. I planned on setting them there.

for a comparison, i made a super wide short fish. 5’0x22. the keels are pretty small but toed way in and canted way out(maybe 15 degrees) and they are a good 3-4 inches forward of the buttcrack. My back foot is behind them and it offers a really strange feeling since I push the board and the fins just drive. depth will control hold a lot more than base will, base will control speed and stiffness. the board is incredibly loose, probably due to the 17 inch wide tail, 14, tip to tip. but it has really good glide down the line. the fins are a really weird template, but the basic dims are 8 1/4x 4 1/4. they have a slightly concave inside foil. If i could do it again I would have put the fins a 1/4 inch back and made the base 8 and the depth 5. If I were you i would make the foil at least a 80/20(outter/inner).

Oh yea. i have never taken the board out in bigger than chest high becuase i never put in a leash plug but i have gotten barreled front and backside, so i geuss it holds in welll enough.

Yes, I agree, purist short twin keeled set-ups do quite well with the fins at or near the split.

Here is a comparison of very different approaches to fin set-ups:

The board in the foreground is a bigger fish. Back in the day we called them “Whale fish” as long as 9’6". I’ve seen Stevie with fish set-ups even longer before going to 5-fin variations. The board above is 7’6" so it is really a Pygmy Whale. Fin position is distorted by my bad habit of using a fisheye (sorry). They are not up as far as it looks.

The keels are up because of length- locations took a lot of testing, cutting off, re-glassing, but in general, the longer the fish gets, the more they seem to benefit from having the fins: up forward, taller in profile, and being toed-in slightly.

Semi-keels are up about 7-3/4" on this one, as the hull length allows for more rail to do the work plus the rider is (should be) up forward more on this length/design. This keeps the sweet spot just ahead of the fins where the rider should be most of the time. If the rider is too far back on the board, then the tail is too wide for the given design and the fins will overload.

The taller fins are a function of reducing the fin base length. These 6-1/4"L x 5-3/4"H semi-keels have less base to take some of the drive out of them (the rail is taking this task on a bit due to hull length). As the bases get smaller, the fin area needs to stay useable, so the keels get deeper.

Toe-in comes into play with more length, kind of like the rear-steering on a “hook and ladder” fire truck. The rear end is allowed to translate side-to-side a bit more to get the longer hull around in a balanced amount of time for the overall bulk of the board. Toe also keeps the fins from loading up too much and too quickly at lower speeds.

The board in the back of the photo is more traditional, 5’8" and with 11" tails and 5-1/2" split. The 8-1/2" x 5" keels are up around 6". As a note, these particular fins do not line up with the tips, but are actually measured 1" in from the rail edge at the rear of the fin. They are outboard of the tips and parallel with the stringer.

Have fun.