Fish Keels Help

I know this has been discussed in depth and I have done a lot of archiving, but I want to throw my board dimensions out for the expertise to weigh in - thanks

I’ve always been in love with the retro lis fish boards even though having never surfed one, but decided to make one to surf. At first I thought the fins would be the easy part, but after archiving on here for hours I realized that it seems pretty technical on the fish so looking for help. I really want to do glass on in keeping with the retro look so want to get it right best I can.


I’ll start with the board. Like I said it is a retro inspired fish. I am 6’2" @ 210lbs. The board is 6’2" x 22 1/4 x 2 3/4. Tail and Nose at 12" measure 17" and tip to tip on the tail measures right around 12". I’ve included a pic of the outlone best I can and rocker. It is completely flat across the bottom from tail to about 4’ then transitions to a slight concave in the forward section. 

I am on the east coast surfing the outer banks 90% of the time. 

I’ve read of the pavels, gepharts, KGs… asymmetrical vs symetrical foils etc… and just really not sure given size, profile, shape, surfing conditions etc… Again first fish and want to get it close at least. Any input would be greatly appreciated. Thanks guys!

Back to archives… I’ll come up for air soon. ha

Hi Curlz-

Are you looking for help on the board? Or on the fins? Or both?

Seems like you’re pretty committed since you’ve started a hollow wood board.

Keep up the nice work!


“6’2” @ 210lbs" big guy needs big fins.  Big boards need big fins.  I think the biggest twin keel fins commercially available have about 25 sq. in. area.  That might be enough.  If you think you need something bigger, put the template on a copier and enlarge it - then make your own custom fins.  Foil 5-8% thick with the thickest part about 20% chord and straight tapered from about 50% on back.  

I have always liked this template from ‘Halcyon’  that I got via ‘Rooster’  here on Sways.

After my fashion, I ran it through finFoil by ‘Hans’ , making them thick ala ‘Thrailkill’ , and did some messing around on the CNC mill to add a resin halo and foil them like ‘Ricky’ has done.

So at least 5 people on Sways have influenced this design beyond my own efforts.  I get a kick out of that. Now I just need a board for them…

I have also received  templates through the mail. That too is a thrill, to know that someone was willing to share and take the time to trace, fold, address, and send.





Hey Curlz,

I don’t have any definitive info for you right off the bat but am in the same situation as you. I’m starting a fish as well and have been researching the right size and shape of keels to glass on. I’m also on the east coast and surf OBX most of the time. I’m shaping a hybrid fish that is not quite a traditional Lis type nor is it a modern fish. I’m 6’, 200#‘s and my board is 6’-21.5-2.75. 16-1/2"N, 16-1/4"T and 12" between the tips. From what I gather, us bigger guys need a little more area to the fin to keep them from sliding out so I went to Blending curves and got a template from there as a starting point and made one that is about 5-1/4"h x 6-3/4"L and after adding fin rope and laminating them they’ll be a bit bigger. More of a swept back modern style vs a straight up keel. Not sure of the total area of it but it’s roughly the same shape as many of the modern keels but bigger. I was looking more for drive in smaller surf than high speed fins. From my reading and conversations with people, you can’t do any real damage by making one larger than necessary, but you can really be hamstrung by glass-ons that are too small. the foiling on them will also need to be correct. I hope more of the experts on here jump in and give their opinion, and correct me if anything I said is incorrect. 

Hope to catch you out on the beach one day… I’d love to check out your board!


Those are some good looking fins jrandy! Love the profile. 

I noticed that they are .60" thick. How do you determine the proper thickness for a given fin? 

Thanks for all the replies and special thanks for sharing the wealth J - super awesome. Those fins look amazing to brother. Really nice work. How do you guys prefer putting the foil on? Belt sander perhaps? I have never made fins, but perhaps I should. I’ll check out youtube to get some ideas. 

Sorry if my initial post was a bit ambiguous. Was reaching out for help on style (KG/Pavel/Gephart/101FinCo. etc…), placement, size of fin and angle. Thanks for clarifying I should be looking for the largest fin possible. That helps. As for placement I found some older archives of guys talking about width of tail really determining fin placement which is why I included the measurements. I am not sure if my fish is a narrow tail or standard or wide without having a reference point. Also read on double foil vs single foil - double being more drive and single being more snap/pivot. So based on what you mentioned wanting PatEilers I think you want a double foil for drive. That sound correct guys? That’s what I have been leaning to as well for mine - drive over snap. Concensus seems to be about a 5 degree cant, but does that change if you put on a double vs. single foil keel? 

Has anyone here tried grinding off a futures/fcs base to convert to glass on? I read lots of post of guys asking the same question with no “yes I have done it” response so thought I would field it again. 

The more I read on here the more I realized it wasn’t simply a “keel fin” on a fish board and since I am wanting glass ons wanted to get it right. I tried finding the thread talking about placement, but seemed to have lost that tab. If I find it I will post it up again for everyone’s information and to bring up good information again for all to have. 

Off for more research and finding some large fins. Thanks again



Cutting off the tenon/tabs of Futures/FCS compatible fins to make them into glass-on fins is a viable option.  There are some options that have bamboo in them available on eBay.

Cambered foils achieve higher maximum lift coefficients than symmetrical foils - more grip - more drive.  Twins are designed to be ridden on edge near those limits.

For longitudinal fin placement, it is easy enough to reverse engineer it by trolling the internet for similar length boards.  Just go to the top board builder’s pages and see where the boxes are placed in the bottom photos of their twin-fin offerings.  Keep the trailing edge of the base about one inch to an inch and a half from the rail.  The critical thing is the toe-in.  About two degrees as measured off the flat on a standard thruster/twin fin is about right.  The problem is that there is variation in the orientation of the zero lift angle of attack from one fin design to the next, and our boards are actually sensitive to about 1/4 degree of toe-in angle.  What I mean is that that small of an angle can be the difference between a mediocre board and a good board or a good board and a magic board.  Twins are super sensitive to toe-in/template/rocker interactions.  Thrusters compensate with a back fin to fill in the void.

If you really want to get fancy and do something super correct when making your own fins, use this foil: Drela AG03 (flat aft bottom) airfoil

If you’re even considering using fiberglass fins then it doesn’t cost hardly any more to order a custom set from a finmaker than to buy a fin system fin.   






Thanks. It looks like I used a NACA0015 foil along with the Halcyon outline. I can say with certainty that the thickness was a result of some things I read here on Sways.

What exactly I read I cannot recall.

Years ago a friend made a 6ft fish for the big guy.   His keels were 3/4" thick.  That board surfed really well.  Very loose for a fish.   

Last year I built a set of fat fins for a 6-8 hybrid type board that I built for him; 1/8" G-10 spine plus (3) layers of 1/8" aircraft ply.    


Question on that - Are you saying a cant of 2 degrees instead of 5 or are you saying to toe in 2 degrees instead of using a common variable such as 3/16th of an inch toe in? Thanks


Some great looking fins guys! Really enjoying the display and seeing everyone’s work…


Did some more searching and think I might reach out and talk with Marlin at 101 Fin Co. His keels are much bigger than most and I’ve always heard great things and wanted to them for a while. 

Going to start looking at Pavel’s twin boards and start searching for fin placement.

Curlz, I was thinking of single foil as I thought they give more drive out of the turns as well as being looser. My thought was to go  with 3/16" toe in and once I get it laid out am curious how close that is to 2 deg. I have blanks glued up for the fins with multiple layers that are now 3/8" thick and am contemplating adding another to make them 7/16" now… maybe thicker? I read how one person had his fins placed 5" up from the buttcrack and it just didn’t have any drive. He removed them and placed the rear edge 1" up from the buttcrack and 1-1/8" in from the edge. Totally changed it and now has a ton of drive. 

Ok, I went and checked some boards - I have toe-in from 1.2 to 4.5 degrees.  The 1.2° fins are fairly thin, they have little camber and thus don’t need to be toed in as much.  My big-water 7’ 4" twin + trailer with Futures T1 fins are set at -2.8°.  I’ve had it in the water a fair bit and it feels perfect.  All my 1990’s twin fins with 9% thick flat inside foils were set to -4.5°.  I surfed them in serious juice that makes the Newport Wedge look tame and they worked perfect.  The larger toe-in is needed for the larger camber of the foils - to get the zero lift angle of attack pointed straight ahead.  Everything else has Futures V2 foils, foils with more radical camber than V2 foils, highly modified flat foils with dropped leading edges added, and the one remaining board with flat inside foiled fins hasn’t been in the water cause I’m too fat for it (I put modern fins on a favorite 1990’s 6’ 5" x 18 1/4" from when I weighed 40# less, a thruster for Rincon).

So, maybe 3° would be a better conservative/safe angle.  The absolute last thing you want to do is have the zero lift angle of attack toed out the slightest - the board will lock up.  Most boards have the side fins toed in too much, but we compensate for it with the back thruster fin that fills in the deadband.

If you have a twin-fin setup where the template is too straight and parallel going into the tail combined with a rocker that is too straight out the back, you’ll need a little more toe-in to keep that from tracking/locking up.

I use a 4’ straight edge to set my lines: 2.5" across 4’ equals 3°.

Hi Curlz. I’ve made quite a few lis type fishes for myself. Can’t go wrong with the Halcyon template or better yet see if he will make you a set. Foiling fins is fun in spite of Greg Tate’s hilarious outlook on the subject. I line the rear edges up with the top of the buttcrack and the tips. For double foils no toe in or cant. For single foils 1/8 toe in and and 4 degrees cant. This works consistantly well for me. Consider I am my own team rider and have never surfed a wave gnarlier that the wedge. I have know idea how this translates to a hollow wooden board. Thank you Scott Jarrett for sharing your knowledge so openly. Please explain what 9% foil is or did I read that incorrectly? Mike

Maximum thickness divided by chord length times 100.  So, a 5/16" thick fin with a 4.5" base is 6.944444444…% thick or basically 7% 

This has been some great information and way more than I hoped for. Thanks to all for sharing so much knowledge. Not sure I would enjoy surfing as much as I do if it weren’t for this aspect of it so thanks.

Scott I went through and through you last longer post and really enjoyed it. One thing I wanted to clarify with you… You mentioned not having your 0 liftpointed outwards at all. I am a helicopter pilot so understand aerodynamics and lift of an airfoil but there are a few different vectors associated that produce your resultant lift. How does one determine their resultant lift vector of a fin in water? So your point being that depending on the camber you have to toe in more or less to keep that 0 lift vector straight ahead - this is what I am not sure I visualize. What is a 0 lift vetor straight ahead? Thanks

Well I went ahead with 101 bamboo fins after talking with marlin and y’all and the archives. I think I got a good start. He had three designs and recommended his g-special. It was the largest and between the straight back and curved/cutaway back. I had him double foil it for me to minimize error on my behalf until I can learn more and experiment. Correct me if I am wrong, but double foil doesnt require any cant or toe in correct?

Well thanks again. I really appreciate the information and support. I’ll be out of town for a few weeks so won’t be able to finish it, but will post some pics early next week as I just glued the top panel on. I’ll give it a good 36 hours before unclamping and shaping the rails. 


We’ll be looking at the Cl vs Alpha plot on two airfoils, the Drela AG09 airfoil that is thin (4.9%) and modestly cambered, and the GOE 265 that is a little thicker (7.7%) and highly cambered.  Look at where the lines cross zero Cl (lift coefficient), then go down to see what alpha (angle of attack) it corresponds to.  The less cambered AG09 foil crosses around -2° alpha and the highly cambered GOE 265 foil crosses around -5° alpha.  The camber is the mean camber line, the average between the top and bottom surfaces, that is drawn on each airfoil plot.  

Drela AG09 airfoil

Gottingen 265 airfoil

With flat bottomed foils, as we increase the % thickness, we increase the camber, so we have to toe them in more.

As for how to figure out what that angle is, I’m still figuring out how to do it.  I thought I had a system, then just recently I looked at some test data and Xfoil predictions and realized I made an engineering assumption error.  I wasn’t far off, but I was off a bit.  It’s all way too involved for this forum.  If you can find something on that looks like what you’re using, then that’ll be close enough.

A way to cheat is to put all the camber into the front 25% of the foil.  That’ll actually give the foil better high angle of attack performance, but then place the back 75% of the fin as though it is a symmetric foil.  You can even make it look like it is a flat bottomed foil.  That’s pretty much what I did when I made my own fins.

Got a ride in a Huey once while working a test mission we executed at WSMR.  The pilot was a Nam vet.  We were looking for something  - didn’t find it.  Afterwards, our pilot chased an Oryx through a dry wash.  Man, those things can run fast!  Felt like a Mutual of Omaha moment!  You’re thinking “Oryx in New Mexico?”  Yep, some rich guy brought a herd over from Africa.

Helicopters do not fly, they’re so ugly the earth repulses them.

Scott, I ran out the flat-bottomed NACA15  foil I used versus the ones you mentioned. Here’s a picture for the folks at home.

Hi Jrandy, Scott,

Are you aware you can load those .dat files straight into the new finfoil version?

More info here: