Re-shape a fin

I don't see why not, as long as you know what you're doing.
But most speed orientated boards have a tuttle base.

The simple answer is no, you will never manage to reshape both the outline and the profile into something that is anywhere near a proper speed fin. Which profile/airfoil would you go for, and do you have a CNC that could do the job?

But you can certainly go fast (+30 knots) with that fin as it is.

A bit different, but similar. I've got a couple of US box pointer fins, 28 and 30cm, that I'd like to change to powerbox.
Is there a conversion kit available?

It could be a fun project - if I knew what to do with it. Certainly not keen to spend big $$$.
Tried the fin for the first time 2 days ago, and it felt planted and solid in a big chop, but once I replaced it with a 36 weed/speed the board just flew. The difference was very noticeable.

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Obelix said..>>>>> So the curve is less important than the profile.

Flex is very important, and the tip of the freeride fin is designed to twist, -- more than you want. So reshape the outline more like the weedspeed, without the backward trailing edge,
something like this.


this will give less tip vortex drag, and reduce twist, improving lift.

Let us know how you go please.
And maybe you could increase the, thickness to chord ratio, to 9% this will be more forgiving in chop.


I haven't directly compared them, but I suspect this foil isn't a lot different to the weedspeed.

You'll probably need to build the middle of that fin up a bit with bog. If you use flexible plastic to spread the bog, hold it tight between leading and trailing edge at the base, then run it up to the tip, with your fingers just on the trailing edge and at almost right angles over the leading edge, this should leave a nice smooth finish, and reduce sanding time. I use a dense flexible plastic sanding pad to get the concave trailing edge. Don't take it down to razor sharp but, you'll regret it later, just leave a 0.5mm to 1mm square trailing edge, don't round it off.

Or just buy a Tectonics Maui.

I've lopped the curvy tail off a couple of under performing fins, and reshaped with great success. But it was more about getting rid of the excess twist and lift the fin was giving, rather than reshaping the whole fin into a speedier profile.


Key points in doing it though, i was completely prepared to buy a proper replacement if the experiment didn't work, and the fin was already rubbish. so no love to lose if they turned into bin jobs.

i was in a similar boat to Obelix i had a rubbish fin but it had the powerbox head i needed, and it was already about the right size. doing it saved me some money.

i do take Surferkris point though, it can be hard to sand the profile of an already shaped g10 fin into another precision speed shape when you start having to worry about how the fin is going to flex at speed. If the chord width profile was already slim, theres no meat there to reshape and maintain stiffness.

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decrepit said..

Subsonic said.. >>>>If the chord profile was already slim, theres no meat there to reshape and maintain stiffness.

Exactly, that's why I said he'd probably need to bog it up.
If worried about stiffness, add a layer or 2 of carbon first.

Sorry decrepit, missed you'd said that. I was thinking more along the lines of a quick "one afternoon" job too though. Completely possible to beef it up and give more material if it is too thin and you have the time to spend.

OK, this is after a hacksaw and some rough thinning . Now for some fine sanding to get the profile right .
It's looking a bit like weedspeed, but upright.

Yes the secret is long even sweeps along the fin, don't take too much off at once, and keep checking the foil over the whole length.

That is actually worse. You will need rough paper to make any progress and then the scratches are so bad you will go thru a bunch of steps with about 4 grades of paper
Trust me. How the video shows. about 120grit on a 5" pad with some give in it ...i use 1'4" yoga mat in between paper and wheel.

Follow the lines like shaping a wind in 5 ply

Get 5ply and make a fin first to get a feel for it (with the machine sander i mean)

should be better than it was, look forward to your review

the ozito one at bunnings for $100. variable speed polisher ) hard to find, everyone wants to sell an angle grinder or a pro level car buffer that costs $400......
Ozito one - speed is good for board work and I can't kill it

@ Kris - well yes, I sail in a chop mostly, so a hybrid speed/freeride should be optimal .

It's likely to be faster than it was.
If not, I'll go to the next step and try to map the fin into Decrepit's profile above.

The fin shape resembles the SpeedWeed, except that the SpeedWeed is designed to sail optimally at the angle, and this is almost upright so may not work.

Will try it on in Cervantes this weekend, although for the race I'm more likely to put on the actual SpeedWeed.

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Obelix said..
Mark, Decrepit, I tried sanding it by hand first with 320... sigh... then by 150...sigh...
then capitulated and put a circular 100 on a drill.
Then again 150 and 320 by hand to make it more smooth.
So yes, using the tools was much faster, although the drill is much inferior to the polish sander.

By hand I'd have used 80grit at first, yes it does leave deep scratches, but you allow for that. Followed by 120grit, that gets it fairly reasonable, then go through the wet and dries 240 to 400/600.