DIY Foil Talk and Knowledge Sharing

Hey there!
I build foils myself but there is little info on the net and that’s why I’m starting this new thread to exchange ideas with you and hopefully find people who are as crazy about building foils as I am!

I got into foiling by buying a DIY kit from Clearwater Hydrofoils, where you have to laminate a wooden core with glass by hand.

That was three years ago. Since then I’ve been hooked on foiling and have ridden a lot of different stuff. Most of it has been Sab, which isn’t exactly known for a very surfy feel. (Which I like, even though I live near a lake where there’s rarely any wind or waves) So I’ve always tried to build my own foils. I started with hand shaped foam cores from tail wings to large front wings where I cut out several sections of foam with hot wire. I stopped tinkering after making a front wing (similar to the Axis 1150) from a 3D printed positive that was lost when the mast securing bolts broke. I remember it was surprisingly good for pumping, which it was designed for, as well as light wing foiling. But it was very flexible and could never reach the level of a professionally made foil.

After this long break in which I was very active wingfoiling and pondering about foils, I started designing foils again by getting serious about cad programs for the first time. I designed the first rearwing and its mold and printed it with a normal 3d printer. I finished the mold with a glosscoat and hand laminated the first prototype. It was surprisingly stiff and what I was most pleased about was that it was incredibly precise compared to the CAD model. This convinced me that you can definitely achieve acceptable results with 3d printed molds.

I tested the foil several times and it did pretty much what I expected. So that was a first success. Here are some pictures so you get an idea how i made the rw’s.

Since then I’ve been trying to improve the technique with the mold. One big problem at the moment is the finish of the mold. If you finish it with a glosscoat you ruin the precision of the 3d print because the layer is quite thick. This layer has to be sanded, whereby even more precision is lost. I am now experimenting with sprayable paints which are much thinner. Do you guys have any experience with finishes on 3d printed parts?

On the other hand, it is difficult to keep the carbon and glass fibers on the mold at the critical points where it has sharp edges. Especially at the leading edge I have the problem that the fiber detaches from the mold and creates air bubbles. That’s why I’m now experimenting with primarily sucking the fibers onto the mold with a classic vacuum laminating system until they are half cured and then joining them and pressing them together. This works better, but with this technique you still have small air bubbles.

My goal is to get a positive part out of the mold that only needs to be cut out and not finished. Do you have any ideas or even experience in this area?

I hope we can help each other as I find that there are very few tutorials and information on this subject on the internet.


Nice writeup and pics! Thanks for doing that. You are making some cool toys. I don’t have any wisdom for you but I will share this link with you of a facebook page called Board and Hydrofoil Building
Lots of pro composite builders on there.


Search for this users posts. “Admin” He’s 3d printing his own designs on custom 3d printers and having success.

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Thanks! I’ll go check it out.

Sounds good!

Nice write-up. I have also made several front and rear wings, originally with 3D-printed plugs skinned with Carbon, and then I quickly moved to moulds and vacuum bagging. This is my current process.

I don’t do a lot of surface prep to the mould, light sand with 240 grit to remove any visible defects, and I use spackle/filler to clean up any join lines from multi-part moulds. This sometimes takes a few coats with sanding to get a joint flush, but it dries fast so it is a single-day effort. I use a brush on PVA release agent which seems to give a good finish.

I lay up each skin of the wing and vacuum bag it, then I trim these to shape with a dremel (add some features in your mould if your trailing edge is very flat to help find the cut line). I then bond the two skins in the moulds via compression (moulds are glued to MDF for reinforcement) with a chopped carbon mix. This means there is no core, these wings are 100% carbon. This construction method lends itself to stabs, or small/thin front wings. Ideally, I would get a good 2 part expanding foam if I ever wanted to make a larger wing.

I use my CAD software to confirm the target weight, and then weigh the skins to work out the amount of chopped carbon I need. Make the skins with enough layers so that the ‘core’ chopped carbon is no more than 10-20% of the target weight to maximise strength and reduce risk of thermal issues with a large volume of resin in the ‘core’. Overfill with chopped carbon, then progressively tighten the moulds over an hour or so to allow squeeze out. Clean up the edges with a dremel/sanding block, hot coat, wet sand and good to go.

I have made plenty of mistakes and had issues (all of my own doing), but I have never had an issue with a delam or water ingress along the join seams, which are invisible.

Thanks for the info!
Do you cut the carbon layers precisely to the shape of the wing (as with prepreg carbon) or do you leave an overhang on the first layers? (as seen in my picture) I believe that this overhang creates the air bubbles because the carbon has to make a sharp curve at the leading edge and so it lifts off the part. Perhaps it is a particular problem with rear wings as the curves are even smaller there than with front wings.

here you can see the air bubbles.

I do an overhang but try and limit it as much as possible, and normally only a few layers as I don’t want the edges to be proud, as you will need to sand these flush with the mould to bond the two halves. Making a template of the profile with paper or masking tape is an easy way to cut your plys to be roughly the right shape and size.

I am no composite expert, but those ‘air bubbles’ look like dry spots that would be easily resolved by even a basic DIY vacuum. I don’t see much bridging at the leading edge. The rest of that top layer looks oversaturated. I apply a coat of resin to the final product to achieve the desired finish, I don’t try and get that finish coat out of the mould

Do you wet out your ply before laying it up, or lay it in then wet it out? WIth CF I find it a lot better to wet it out first on a plastic sheet, then transfer it to the mould layer by layer.

I wet out the mould and then put in every layer and wet each one. Then i put everything in a vacuum bag with pealply and fleece. When its half cured/tacky i take it out of the vacuum and fill it with chopped carbon. On the first prototype i tried to finish the wing with a glosscoat but it was quite thick and i kind of lost the shape of the airfoil. What hot coat do you use? Ill give it a try!

Do you know the resin : ply ratio you are using? I do about 1.1 to 1, then pull a full vacuum with perforated film. I never wet out the mould first, but I ensure my ply’s are fully saturated before I place them in the mould.

If you are bonding the two halves together with that overhang you will lose the airfoil shape. Try letting it fully cure, then trim it to shape and bond with chopped carbon later. As long as you are using pealply you will get a good mechanical bond.

I am patiently waiting for someone with a lot more experience than either of us to jump in and point out all our mistakes!

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What foil section do you use for the foil and for the stabiliser?

Regarding your layup:
Check your work environment temperature, higher temperatures, lower resin viscosity, less porosity…
Degass the resin under vacuum to remove the air entering during the mixing process
Use an in-mold coating
Wet out the mold with some resin
Add a first 49gsm glass layer to further improve the surface quality - cut your fabrics to size
Add carbon as required
vacuum bagging… to remove excess resin and to compact the layup

Hi, you foils look amazing! I just started my 3d printing career :wink: partly because its easy to print cores or molds for foiling. I recently a random car part carbon fiber video, where the guy used car vinyl wrap on a 3d printed mold to hide the layer lines. I tried with a mold for a stabilizer and it works very well. The wrap has a carbon fiber look, but its just wrap you can apply with a squegee. its self adherent and easy to use. The surface you see on the picture came fresh out of the mold. I had some paper on the back of the wrap, you can see it in the mold and on the half of the stabilizer. There are some small scratches because of the silicon squegee i used on the wrap. I used some wax for part release, which was very easy. I did have some Air in there, which im not sure where it came from. I think the Wrap has small holes in it to releas air. By putting it in a vacuum bag, i might have drawn tiny bits of air between the layerlines and the wrap into my wing. I will do further tests :slight_smile:
i can also recommend the facebook group