Fin exploration

Maybe some of you surf fiends might find this info interesting, maybe not.

I’m a 23 year old surfer/kneeboarder from southern california. I’ve been in and around the ocean since age 6.

Sometimes I get pretty inspired by all the knowledge you guys here have, and all the cool stuff and craftsmanship going on.

I don’t have any experience with laminates other than fixing my own dings. But I do have some experience with metals and mechanical stuff.

The last six months I have been surfing my 6-0 x 12 x 19 3/4 x 15 x 2 3/4 single fin (what amounts to a heavily concaved CI single) a lot. I have surfed probably 2 months each on a 8.5" tk flex, a 9" stage six (refoiled by me because the stock one wasn’t square enough for my liking, the result being the ‘paddle’ coming out a little more rounded.) and one of rich’s 7.75" mentals a fairly stiff base with more flex at the tip. All fins are valid designs but I spent most of my time on the mental or the paddle. Mostly because the fin tab on the tk is in the front, limiting maxing the fin forward.

The conclusion I have come to with all of these fins is run the fin as far up on the board as possible, and adjust your weight distribution accordingly.

A couple weeks ago I became curious as to what a fin out of aluminum would run like. I found some scrap 3/8’s 6061 t-6 (went to get 5052 marine alum on a suggestion from solo but they had no remnants of this type) for 15 bucks.

Took it home and cut out a 9.0 stage six (I actually added 3/4" of depth to the paddleoutline, and notched the base allowing me to run the fin an inch further up than the box would allow) with a jigzaw, and sometimes sawzall, then got a’ grindin’.

4 hours later I had a damn square alum version of the stage six.

Observations: Weight is 13.5 ounces. The original glass version was 8.5 ounces.

A stereotype of Aluminum would be ductile, soft, and weak. But with heat treatment that thing is solid. I locked the glass version in a vice and could flex it 3-4 inches at the tip, relative to the base, until I heard the faintest crack.

With the alum (keep in mind the foiling was very similar, actually a hint thinner in the blade) I could barely budge it an inch while wailing on it with an open palm.

I surfed this thing in pretty weak waves and could turn as hard with speed, and link as many turns, as with any other fin I’ve had in the board.

Well I kind of learned all I wanted out of it so I went all out and freakazoided the thing for fun.

I cut an inch (squared up to the base)off of the bottom tip of the blade. The result is a little wedge that resembles a 5 fin bonzer side runner. I made a pair of these and welded them to the base in a miniature upside down y style. Also made 4 relief cuts in the leg to encourage twist in the right direction.

Surfed it today in chest-head high lowtide semi mixed up but some fast walls to race waves.

Observations on first go out relative to how most fins feel in the board:

slower paddling into waves (increased area/drag)

more difficult to go rail to rail, change direction

First couple waves definitely noticed the nose kind of lift on the pop-up/upper half of wave on dropping in. This could be from poor angled attachment/foiling of where the 3 planes come together? Or natural occurence from more area in the tip?

Frontside bottom turns (on waves with some push) had heaps of drive. Some waves I would take off deep expecting just to feel a little bottom turn on the closeout, and ended up making the section (or two !). (no wiggle or two-stage, just angle, drop and even pressure on the bottom turn)…it was very noticable that I covered a lot of distance on a bottom turn. Seriously, one semi-holow I dropped in, ran it a bit into the flats, leaned, kicked out and I was like 40 feet from the people at the peak. Like running the TK Flex mid-rear-box, but not as stiff on topturns or cutbacks…you could still overpower it if desired. Extremely fast and lifty(?!) feeling when roller coastering/racing sections. Also, took off one one of the bigger sets (good shape) kinda doubled up-hollow, someone hooted, the heart raced as I went over because I have slid out on bottom turns in similar situations, with fins further back than I was running. Out ran the goddam section in one smooth bottom turn, kicked out. Pretty stoked feeling to be leaning on something you’ve built with your own hands and not eat sh!t!

Overall these experiences have been educational and fun. (you get stoked wondering what its gonna feel like the next time you surf). Nothing mind-blowing but interesting and I made some surprising sections and did a couple ok turns.

Pictures and updates to follow…

edit- oh yeah, this was all standup stuff I only kneelo 10 percent of the time on certain waves in certain moods.

This is cool.

Pictures would help a lot, especially with the last step (the welding of the Y on the alum base).

What is the distance from the tail to the front edge of the fin base with it maxed forward? I’ve been measuring this a lot lately on all kinds of singles, and on shortboards with experienced surfers it runs about 12 inches, going around 14 inches on 9-10 foot boards.

Blakestah, the leading edge of fin is 14.625" (!) from tail.

What you have said is very interesting, as that is the range where the other fins worked great far up in the box.

I would imagine When it felt nose high and slowish the first couple waves I was surfing it how my body and mind remembered those former setups. Then when started noticing the drive I was probably way up board. Man I need to get my brother to take some footage someday. Just got to find the top-turn/cutback sweetspot by throwing my weight (or stepping a bit) back.

Just got up from a post surf nap. 5 hours on two different boards today until I couldn’t paddle anymore. Crawled to the tideline and passed out for 15 minutes, head spinning. Then got my ass up, got some carne asada and an ice cold pepsi, came home and wrote my first post then crashed. One of those days that couldn’t get any better, even though the waves weren’t amazing…

The first pic is before “Dobbs went crazy and wrested the controls away from McWatt”

The rest are obviously, the rest.

nother pic

So you know, by playing with the vertical angle of attack of those little attachment fins, you can either create positive or negative lift on the tail. I’ve never gotten a starfin to check if they are for lift or drag, or just to stabilize the rear end vertically (which, btw, a turbo fin does also, with a tunnel). But if the nose is tending to ride high, probably it is because those little fins are sinking the tail by angling down. This probably slows you down too. I would guess they need to be VERY close to the plane of the board in vertical angle.

But that addition gives the fin a new dimension of action - up/down on the tail - and that is valuable. There are side-wings on many waterski fins for a similar reason - they’ve never caught on in a big way with surf fins, although I am hearing from one longboarder after another how cool they are finding the Turbo fin to be.

The slots are helping the drive, quite a bit I imagine, by allowing the fin to flex in turns.

Very cool - keep at it.

The angleof attack- yes, I double checked before attachment running a square off of the base, even double checked how much the base tilts when snugging it up good in the box. So its the best I could get it, burnt the hell out of my finger holding it to tack it! (couldn’t figure out a way to jig it up/secure it with all the weird angles/varied thicknesses of the components.)

Whats amazing is the infinite variables - I mean that angle is tangent to the rocker of the board only at the attachment point on the fin box.

But as you all know everything changes when you throw a wave and a rider at it…

The Slots- I got that idea from gws over at -er. A real good guy. After he told me about those I saw a picture of some board with them on the fin somewhere within ‘

My next idea I’ve been thinking about is: take a paddle fin and split it down the middle (front view) creating two thinner single foiled fins.

Connect to a single base a la velzy v-fin upside down bonanza light aircraft tail and see what happens… I was thinking the two at 90 degrees to each other.

When you have the board on a 45 degree rail you would have one fin vertical lifting sideways through the turn, and one horizontal adding upward lift to the tail in general.

“Could be heaps better, could be awful, nothing ventured nothing gained, if you don’t try you’ll never know.” -gg

Wow could you imagine if part of everyone surfer’s quiver included stuff they went out on a limb and came up with and tried themselves? This site sure is a great way to share all those failures and findings I reckon…

Any input on that v-fin idea would be cool (negative input/cons are appreciated as well)

The angleof attack- yes, I double checked before attachment running a square off of the base, even double checked how much the base tilts when snugging it up good in the box. So its the best I could get it, burnt the hell out of my finger holding it to tack it! (couldn't figure out a way to jig it up/secure it with all the weird angles/varied thicknesses of the components.)

If it is in plane before it is loaded, is it possible the fin is bending back under load, thus sinking the tail? Perhaps an unintended consequence of the slots? Forces on fins are surprisingly high. In any case, consider creating lift with those footballs instead. You will get lift for much less drag with a foil on the fin tip than you will through the hull. This will cause you to ride a little higher on the water, and a little faster.

This is why I mentioned the Starfin - I’ve never looked closely enough, but I’d bet the winged keel is at a 3-4 degree AOA for lift. The concept that you can have a hydrofoil as part of your fins, which creates lift, and reduces planing area, is an interesting one.

Turning power is all about angling fins relative to the stringer line (rotationally), and position under the hull.

I predict the V experiment to be tough to turn. But, I’ve been wrong before, and am always willing to listen to results.


No they are pretty solid. If i just welded the front half of them maybe but I tried to wrap the bead pretty good.

The Slots? Dunno. If after tweaking the little wings it still feels funky (lol which I’m sure it will), then i can always weld em up and foil the whole thing thinner to increase flex (also decrease thickness, weight and drag…hmmmm)

Yeah I’ve been itchin to try a starfin too but no funds.

Waves this morn- smaller weaker mixed period. Waist to shoulder high. Some sets were absolutely worthless mush, some would jack on the inside sandbar and have decent feeling hollow pockets.

Continued observations (a lot of these seem redundant to what we have already concluded):

I am positive whatever is going on the tail is holding in more than usual.

I can definitely notice the fin hates weak spots, but late hollow takeoffs and hollow pockets (some closeouts) it holds really good- later takeoffs are way easier. In the past it has been quite understood that the relatively straight rocker and wide tail makes it no stranger to eating sh!t. With this fin it is noticably more controlled in critical sections (considering how far up it is).

This isn’t neccesarily good- the thing feels downright thruster draginess through flat spots. And on a backside snap I totally bogged it (felt the nose come up) on the downswing, where it normally would swoosh right around.

I held it in a deep laundry sink and shot water stright on into the point where the 3 planes meet. The water leaving indeed was coming out angled high (which would be towards the board holding the tail into the wave) One word DRAG.

I have no desire to surf the fin again in current state unless I felt like tube riding the board, but of course there are better boards for that job.

So, as you have already known, the next step will be to get some lift.

Originally I foiled those little guys as symetrically (double-foiled) as possible hoping to acheive a very neutral effect as a starting point. They’re pretty small overall on purpose as well.

Before I change the angle of attack I will first clean up the fillets a bit more and possibly flatten the bottom sides (single lifting foil) touching up a nice curve on the top (I pretty much imitate foils on other fins I have to look at not made by ignorant kids like myself).

I’ll try to get the water to come off straight off the back, maybe with a hint of lift in the sink, then surf it again. If the nose still lifts I will start changing the aoa by slicing, tweaking, and re-welding.

Man all this is too complex if I was smart I would just get a mat and find an uncrowded point.

Thanks for your feedback Blakestah.

I sat there in the garage for a while staring at and rechecking those little wings…

I swear if anything the aoa is on the side of lifting, not sinking; relative to the base. Which should keep that nose down. It really kind of perplexed me.

So onward and upward, I wanted to feel it with the slots alone. Off came the wings and re-shaped to a 9".

Foiled it overall way thinner (down to 10.5 ounces). I ran the downside of the foil in the leg way closer to the leading edge, that thing is easily noticable as thinner then the orig glass fin. Got the blade vs base flex to like 2.5" with a good wack, (remember original glass is 3-4).

Found the limit of the Alum. Extended the lowest slot another half inch, put it in a vise and beat it, thud, deformation! Welded back up to original slot depth and left a extra 1/8 indicator (to flip in the water and notice how fatigue wear is coming along per session or even per wave.)

Surfed it yesterday in beautiful chest high afternoon glass. Went great. Some were worthless mush but was able to squeeze two or three turns to the sand. No crowd. Stoked. Still didn’t break the indicator but the faintest little crack is barely visible.

I think, (as lots of your older craftsman probably know), that Alum isn’t lively enough. It has enough strength to function, and in certain application can be structurally more sound than glass, but isn’t gnarly spring material like i imagine some sort of carbon-epoxy fin witht the weave orientated to encourage flex in the right direction, etc… Then again surfing it in some minimalist waves that loggers were having to fade the

hell out of I could still do as many turns as with any glass fin I’ve had in there…

I have not abandoned messing around with some sort of small wing system yet…

  1. I need to get and surf a starfin. To examine its design features and more importantly feel how it surfs.

  2. I need to have adjustablility (the sheer ease of attachment and mechanical possibilties of a metal fin might come in good here, weldability, tappabilty for mini-worm-drive elevators? who knows…)

I’ve already been out there (that second day) after 2 waves and wished I could flip the board over and change something to feel the difference.

So far so good, I’ve learned heaps, and still have a bunch of ideas to work on think about someday learn.

What stoked me more than this is yesterday I bodysurfed a 3 foot mushburger from the outside all the way to shore…the furthest I have ever bodysurfed on a wave that pathetic, maybe 60 feet just with me vipers, some old longboarder guy was looking at me funny because I was getting longer rides than him…of course half the time I had to butterfly and kick like a madman…interesting stuff…

Titanium (especially higher strength alloys like 6/4) can elongate much further than aluminum or steel before breaking, it would be a much better material.

But a lot can be done with glass and resin, too.

When considering the aoa, you probably need to consider the surfboard angle from water entry to tail, and not just tangent to the point of insertion. But, if I were doing it, I’d check the Starfin first, and go from there. The $45 may seem like a lot, but it will be VERY valuable in terms of time saved. You can safely assume they’ve tweaked it a lot already to get it where it’s at. The pics at

look like there is a 5-6 degree aoa for lift.

Cool Thread nice feedback. I wonder how much torque is involved in both the XZ plane and the XY plane at the base. I’m sure it’s pretty significant.

Run – great stuff. Where the heck are you in SoCal(?) I have a starfin you can try. I don’t surf it all the time but I often encourage people to try it, because it’s so different compared to a “normal” fin…

I was thinking, you might consider trim tabs on the wings so you can get the angle of attack dialed in without have to weld…

Hey thanks guys,

Heh titanium would be awesome but too expensive for my taste and I would need tig equipment with an inert box to get down and dirty…always wanted to test out those theories of ti and magnesiums’ flammability though lol

Keith I’m in the south bay but don’t surf much around here anymore…only for convenience sometimes. I burn lots of gas unfortunately, mostly heading n. (sorry northers) That is an awesome offer, but once I get through an insurance payment and my damn car registration in two days, I probably will be able to spring for my own…totally appreciate it though amigo.

Torque, eh, well I have a feeling once we get some waves with some push again that thing is going to break. The first time I re-welded that slot I didn’t grind for penetration enough, and I deformed it with two solid open palm punches in the vice. Second time went 100% and is holding like a charm…we’ll see how long it lasts.

Basically the weakest link is that lowest slot cross-section, which is 1/4" x 1-1/4" of material which has already been weakened by excessive welding and punching.

I catch your drift on the trim-tabs/or adjustable elevator in general. I’ve been meditating on how to rig up something low-profile but strong…so I can take a wave kick out and say “Fricken nose still comin up! Oi!” And whirl a miniature all-thread with a mini lockwingnut until I hopefully can nosedive, then eventually find the happy medium or something. This may take a while. Thanks again

I’m thinking the wings with a central tab. The foil with a slot to receive the tab and recessed pockets outside to receive a geared insert that will engauge a radial rack EDM’d into the side of the wing’s tab. All you need is an allen key to adjust the angle of attack in the water.

so, Run… what’s it going to take to talk you into making some hydrofoils??? I would love to take a shot at it, but I have no metalworking skills to speak of… It sure is intriguing to watch those things.

Run, I have made and ridden a split fin like you mentioned and it went unreal. It was on a modern shortboard and I was using very rakey fins at the time, a la Greenough and early McCoy. 90 degrees was too much though for full size fins. I used around 60 degrees, and even then had several attempts at getting them strong enough to handle the forces, glassed on, not boxed. I ended up reducing the fin area even more to compensate for two fins.

My reasons behind doing it was to find out if the fin tips near the rail theory gave similar response to a thruster, but with the smooth stability and rail to rail transition of a single fin. And it worked really well, very smooth and turned easily. However it lacked the positive drive of a vertical fin, so I added a small vertical trailing fin, same profile but about 2/3rds smaller. It worked really well and led to the in-line setup I use today. The manufacturing hassles of the split fin led me back to vertical fins, but the fully redesigned in-line setup works just as good. Fin design and positioning are the key elements.

Made some great progress today. Only burnt $6.50 on scrap 1/4 x 4 x4 chunk of angle Al and some 1/2" round stock and 5 more bucks on some set screws and a 10-32 tap.

About half-way done, still have to foil the split fin I made out of the angle (think 2 fcs g-r’s 90 degrees to each other linked at the base. It is one piece, the front majority centerline notched with a tab at the rear. Two little chunks of the 1/2" al round stock will be foiled bullet shaped, split a bit down the center, and welded half-on half-off the rear bottom edge of the paddle foil and drilled and tapped for 1.5" long x 3/16" set screws on the top and bottom of the rear fin tab. The front of the fin will be welding to a rotatable bushing (1/2" raw stock again) at the front.

This design should give me 15 degrees of hex-key-necklace-in-the-lineup adjustability in either direction, though I am leaning towards 20 for lift and 10 for sinking the tail.

There will be of course drag and turbulence and weight, but I still think the adjustability factor positively outweighs the cons, and believe it or not the added items are pretty low-profile from a front view. Viewed as just a weird test fin I think it will be interesting.

Wildy sounds cool! Inline trailer, eh?

Tom I dunno what EMD means, and I have no real machinist skills, or access to heavy duty equipment (mills and such). Hell my welder never really was even designed to weld aluminum, I modified it a bit.

Keith as you can see from the above sentence, maybe someday when I rob a bank and put together a bitchin’ shop…

will keep you guys posted.

edit-oops “EDM’d”


I have a starfin you can try. I don’t surf it all the time but I often encourage people to try it, because it’s so different compared to a “normal” fin…

Are you guys talking about Cheyne Horan Starfins (circa 1985)?  I've got these on my 9'2" and 10'8"(see pic).  I reckon they feel a lot driveier out of turns and more don't draw out the turns like a traditional swept fin.  I've been hooked on 'em (and variations) since '88.  

Bought my first in Oz and when that broke made my own until I found a nice Texan on alt.sufing who sent me a box of five. I am now on the last one, so if anyone knows where I can get 'em??

Yes, same fin. There’s at least one for sale in an ad here on swaylocks, just look under “marketplace”. I bought one in Hawaii but that probably won’t help you much…

*Last week surfed my ‘drag fin’ hehe, no it really surprised me and actually held-up structurally in some semi-powerful dumping head high lowtide garbage…tuned it in the water with a little hex-wrench, everything worked and held snug like planned.

Interesting feeling, definitely could feel it keep that nose hugging the surface with the lift in the tail.

And you could feel the intensity of that sensation lessen by centering that aoa.

Is it where its at? No. Too complex, too much drag.

I was maybe imagining maybe it could plane up and accelerate once it reached a certain speed, but so far that doesn’t appear to be whats happening.

Instead of functionally lifting the whole board in a balanced manner (reducing drag in the process) it feels like it either sinks the tail or ‘sucks the nose down’. But I haven’t surfed it enough to explore all its potential.

But it expanded my awareness of what my board feels like in said conditions. It satisfied my curiosity and the questions I had. Viewed as a learning tool, it did its job. AND it got me so stoked to get out there in crap, just to feel it in bottom turns, that I ended up getting a couple 40 foot rides, beats being indoors but still would’ve surfed a mat in those conditions and would’ve been more stoked, maybe should’ve bodysurfed.

Just want to get it in some big faced waves to see how it does on a rail, then its on to research heat-treatable stainless steels…

Aesthetically and functionally I don’t dig it too much. Will post a photo shortly. I really want a ac capable tig machine to experiment with metals the way I want to. In time.

I still want to try that v-fin setup, with the trailer idea in the back of my mind from Wildy.

Still need to get a starfin.

So much cool stuff to imagine and try. This could take years.

Thanks again for all your input.

Edit - for a fin this far up it feels pretty controlled, wish I had another foot of fin box to experiment with someday running setups further up.

Aye she’s gettin’ pretty beat as you can see. Pretty stoked with the practice on hand-foiling if nothing else!

*edit- I didn’t surf it yesterday, i last surfed it a couple days ago.