Hi,
I was wondering if this fin could be re-shaped for speed?

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

Speeds fins regularly come up for sale used at very reasonable prices. Even if they are not the latest model, they would most likely work a lot better than a modified free ride fin.

But as Decrepit says, almost all second hand speed fins will be Tuttle base. Not the end of the world though, as it would most likely be easier to rebase a fin to Powerbox base, than to do an effective reshape of another fin,

www.seabreeze.com.au/Classifieds/Search/Windsurfing/Accessories?search=B4QaJSqfKLbmwaCbTWGZzNR3GrOrK1CR&page=1

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.

^^^ Why not?
Plenty of fins have been hand foiled over a long time and for a long while pretty much all the prototypes were hand foiled.
I make a wave fin from a (larger) G10 fin that is damaged, in around 15mins. With some practice its very do-able.

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?

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SurferKris said..
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.

As Mark Says, my hand shaped fins have done over 40kts, you don't need CNC, and all you have to do is ask,
This is the foil that has done over 40, it's a modified eppler by yoyo.

You just need to print this out in a graduated length range to suit your fin taper, then use a shape gauge to compare fin with foil, a bit of patience will get you there.

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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decrepit said..

SurferKris said..
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.

As Mark Says, my hand shaped fins have done over 40kts, you don't need CNC, and all you have to do is ask,
This is the foil that has done over 40, it's a modified eppler by yoyo.

You just need to print this out in a graduated length range to suit your fin taper, then use a shape gauge to compare fin with foil, a bit of patience will get you there.

Oh , there we go. This seems real. Thanks
So the curve is less important than the profile.

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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.

I use to thin out mid to trailing edge, then just a bit the leading edge, and they would be much faster when powered, lose a bit upwind in angle, and spin out when underpowered heading upwind.
More specialized, less all around range.
You always give up a bit to add a bit

Or just buy a Tectonics Maui.

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Mark _australia said..
I make a wave fin from a (larger) G10 fin that is damaged, in around 15mins. With some practice its very do-able.

Yes, wave fins and free-ride fins are fine to reshape a little, but not a dedicated speed fin.

I'm simply assuming that those that actually have the knowledge of making good speed fins would not place a question like that here.

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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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.

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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.

Thanks guys,
I'll first re-shape the outline as per your drawing, then see how it's going, then start sanding it down to match the profile drawing.
It's pretty thick 3/4 of the length across. May not need to add to it. Plenty to work on to re-shape the profile.

Forgot to say, it's going to be used on the Rocket 115. I don't have any tuttle base boards.

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.

Sanding - fast speed and fine paper.

I use a variable speed polisher - not angle grinder - with a soft pad and about 120grit to start

Sanding disc in angle grinder is not flexy enough it will dig in and be lumpy.

I can't find the video I wanted but this would have to be a help

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.

Thanks, I feel that I would quickly destroy it . Actually, I'm sure I would
May just do is slowly by hand. G10 sand off nicely with some patience.

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)

The bottom 4-5cm may still be a bit too thick, but it's easier to take more, than recover if I take too much.
Can't wait to try it
The photo against the light.

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

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Mark _australia said..
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)

Crap .. sounds like I need to get a new tool for the garage.

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

Glad to see that you are happy with the modification. :)

I seem to have misunderstood the question, as I thought you wanted a proper speed fin. What you have there is, to me, an emulation of a free-ride pointer fin.

@ 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.

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.

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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.

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SurferKris said.. >>>>> as I thought you wanted a proper speed fin. What you have there is, to me, an emulation of a free-ride pointer fin.

Depends on your definition, of "proper speed fin"
The optimum design depends very much on the venue. Try using a standard upright fin at Lake George, and you won't get very far. Slowy's weed speed is very fast, and as said it's designed for annoying surface weed, where an upright fin would continually need clearing. Oblix's fin has less rake, so won't clear weed as well, but it shouldn't be too hard to jump it off.

Any way it's a learning curve, I'm all for experimentation and learning new skills. If it works it will be very satisfying.