Square-Cut Fins / Leading Edge Technology.

Here’s something for the fin boffins and its a real blast to ride.   I took a standard G2 and built up the leading edge at the base with epoxy and microballoons. Foiled it to match and rattle can spray.

The overall fin area is changed a fraction but it makes a big difference to the way the fin works, straight away I noticed the board reacts faster to input. Same drive and hold and all that but it’s lightening under your feet into turns. I’ve tried them on a longboard, prone and a shortboard with only the left fin altered and the standard right fin used as a comparison. It’s subtle in its visual impact but significant in its performance. Anyone seen this done before ?

We did some airplane wing looking fins @ Brewer 25-30 years ago,

Had a Quad and they were good.

Hard to sell them as they were square.

Never stuck around.

They look cool.

Only worried about the blunt tip @ the base.

But you never know.

I really like the look of that center fin.

Give us a ride report.

 I remember those angular fins , too many angles I thought. I often sit around drawing stuff and I tend to redesign the Whole item but I was looking at a side fin and thought what could change without ruining the basics of height, base, rake.

In essence, the basic fin shape does what’s needed and redesigns tend to change everything that’s good. Most popular fins have a similar outline that set the personality of the fin. All similar, but we all know those small variations make a difference and outlines are a balance between drive and turn.


What is the reasoning behind this bump?

Is it similar to the FCS C-drive concept, but then implemented on the leading edge?

I see some small improvements, you can reduce drag by bringing the apex of the foil forward where you added material on the leading edge. However, this will only have a small effect.

This kind of experiments is very interesting! The foil can always be optimised afterwards.

Thanks for sharing!

ordered  a large quad set from Australia for my new LaLa Gemini.

Figured if Maurice can use them on his super concave boards in triple overhead I should give it a try

noticed they seemed to work way better on the forehand, lots of drive and super loose and super fast off the top but backhand they were way to squirrelly for me. not enough drive, probably don’t surf vertical enough backside and more down the line with super late bottom turns. 

Overall a suprising and satisfying experience.

I think the Cdrive tips are too small compared to surfoils experiment. Is that a johnny (forget his last name) singlet?


The base leading edge of the fin, is where your turning response initiates.      The more rapid turning response you experienced is a result of the higher AoA of the leading edge of the fin base, in relation to the bottom of the board.        Also referred to as the angle of incidence of the leading edge of the fin.     A very revealing experiment.       The change in performance, can be clearly attributed to the change in an existing fin.         Well done.    

Bill, thanks for the props.

I rode them again today, heaps of waves, swapped boards from a shortboard to a longboard and the fins still make a positive difference.  It’s just quicker into every turn,  theres a definate difference, a perceptible speed change between starting a turn and having the board follow.  After 6 or 7 waves you start to feel the original fin is slowing you down. :wink:

I’ll keep testing them just to make sure and I could make 100 variations but I think this feels great as it is. I might make a few sets and hand them out, what’s the most popular fin shape, and with a FCS or Futures base ?




surffoils you tried this on bigger FCS fins? like an AM2, Sunny, Rusty or likewise?

I’m wondering if the rake is as important

not trying to be negative, but isn’t it possible you just stiffened up an otherwise overly-flexible fin?  Those black plastic FCS fins are fairly soft to start with.  Suggest maybe you try shaping some fiberglass or G10 ones with your new template?

Oneula, no I haven’t tried it on bigger fins but I will. Interesting to see if the effect is magnified if I do it on all 3 fins or just the side ones ??

Keith, I’ll try it on some glass fins just to be sure, good thinking that it could be a result of less flex.

If anyone is keen to have a try here’s the DIY steps.

Outline on paper.

Front line isn’t vertical but 10 degrees tilted back, and mark up 30mm from the base line.

Connect the 30 mm Mark with the leading edge. Put the fin over the paper and Glad Wrap and build up with resin and micro-balloons. Shape it down to the line with a slight curve added to each line and round it off where they join. I’ve never believed that straight lines are as good as curves, even subtle curves. Foil and spray.

Oneula, that centre fin is a Johnny Rice, a very smooth fin in any board over a 6’6" egg. 9.0"

yup I thought i recognized it didn’t he call it his “feather” fin?

I have a big one on white

always wondered how it compared to Greenoughs paddle or the squirrel fin from florida

I think Johnny Rice was native american and used to have a signature model on surftech

kind of disappeared from the scene lately but he was a charger 

It’s working like mvg’s, tubercles, or other leading edge filets, which help disturb the flow, helping it stick to the fin, reducing stalling from flow seperation at high angles of attack. On another thread someone mentioned “spin out” as a result of stalling, but stalling is simple when the flow seperates and the effectiveness of the fin for turning stops. Bill’s been on to this in his own way for decades.

Oneula, there was a small town shaper here in Aust. Called John Rice so I thought it was his but your information rings true.

I’ve make a bigger version of square-cut fin. The area added to the original fin on the left is 3%

Cool stuff!