Long post- if you are interested in building a carbon foil and have limited experience, this might be worth reading. Otherwise, maybe skip this one. I've read a bunch of posts from people far more talented than me, and they were extremely helpful, but many were written by people who assumed the reader knew what the hell they were doing, and I did not. This is by a clumsy hack for clumsy hacks.
I've been riding a Zeeko aluminum foil for a couple years now, pretty much all I ever use anymore, and also the only foil I've used. The fuselage got pretty bent out of shape after repeated grounding while learning, so I decided to make a single piece mast+fuse out of carbon. I am using the stock Zeeko wings on it, I think wings are best left to the professionals. I don't have any real experience with composites, and I don't have access to any fancy tools (this was done mostly with a hack saw, sand paper, and hand drill). I also don't have a garage, much less a work shop. I did this on my living room floor with a piece of plywood as a work area. Vacuum bagging was done with a vacuum cleaner and extra large vacuum storage bags ($10 for 2 on amazon). Mast is about 13mm thick and total weight of t-bar is 1.2 kg, or just over 2 kg with stock Zeeko wings (g10) attached. Had my first ride yesterday, and it went really well. It is so much easier to water start a light foil strapless. Foil is totally silent (so far). My aluminum mast occasionally sings, but not much. I made the mast about 2 inches shorter than stock mast because I ride mostly in shallow water, and I think that was a mistake, but aside from that it seems to work as well or better than stock mast/fuse.
Summary of process was: shape mast and fuse separately out of balsa, reinforce area of fuse for front wing inserts, layup the fuse, attach mast to fuse, layup mast, attach plate to mast, layup plate.
Materials: unidirectional CF (5 oz), Triaxial CF (6 oz), twill CF (6 oz), 0.75 inch diameter CF biaxial sleeve, a few pieces of 1/8" balsa wood, system three slow hardener epoxy, micro balloon for thickening resin, vacuum storage bags (48") from amazon, a few cheap m6 titanium inserts from China/eBay, some wood glue and gorilla glue. Peel-ply and bleeder cloth are optional, but I think worthwhile. Also gloves, lots of them. Total cost was about $250 and I have some left overs for my next project, all composite stuff was from compositeenvisons.com. 3 yards of 24 inch uni, 2 yards of biaxial sleeve, 1 yard of triaxial, 1 yard of regular cheap twill is enough fabric.
Warnings- I am pretty light weight and free ride strapless. I did not try to make this foil any stronger than strong enough for me. Don't follow this layup with a long mast and race it, it will probably snap. In fact, don't follow this layup at all, because I have no idea what I'm doing with composites and I've only tested this once so far. Also, I've only grounded it lightly, I don't really expect it to survive a proper grounding. My foil is really beat up, so I don't really care if I lose my wings.
1.) shaping mast and fuse-
Mast was three layers of 1/8" balsa glued together then sanded down, fuse was 4 layers of 1/8" balsa. I made a template of my existing mast by taping sand paper over it and rubbing wood over that. I tried glueing sand paper to the template to shape mast, but a sanding block for shaping mast was much faster. I got a decent approximation of a foil shape in about 30 minutes, by no means perfect. Fuse was shaped as a square with rounded corners, except the very front which is a bit shorter to accommodate the front wing. It tapers to a bit thinner at the back.
2.) special treatment for fuse inserts-
My first attempt failed because the inserts twisted around inside balsa and cracked the fuse (in stress testing before I ever rode it), so I knew this area had to be beefed up. I put two layers of twill carbon over where the inserts would go (just a couple inches long), after it cured, I carved out all the balsa for the three bolts and filled it with chopped up carbon fiber and resin, and allowed inserts to cure in place. To get insert placement right, I covered wing in plastic wrap, put Vaseline-covered bolts through wing, and inserts on bolts, then clamped the wing to fuse while it cured. After this cured, I then put a couple layers of carbon over all of this, back to where mast would join. Once the inserts were cured in place, I put bolts covered with Vaseline in them so I didn't get epoxy on threads in subsequent steps, if these extend only a bit past inserts it is easy to wrap carbon around them, otherwise put dry carbon in place, then put bolts in, then wet carbon out. Bolts should not have a head (just a threaded cylinder).
3.) layup the fuselage
Fuse is 2 layers of 5 oz uni and 2 layers of 6 oz biaxial sleeve. Front and back have an extra layer of each. I'd have done 3 full layers plus extra at ends if I'd ordered enough material. The sleeve works great on the fuse, but it has to go onto a dry surface, so I did sleeve over balsa, wet out, add 1 layer of uni, cure, then repeat. The fuselage I wrapped tightly with electrical tape (sticky side out, away from wet carbon), then poked a bunch of holes in tape with pin to let excess resin out. This worked quite well, if I had a proper vacuum pump, I'm sure that is better, but this was fine. Take the time to find extra wide electrical tape, it works much better. Once this is all cured, drill holes for rear wing. I think this would be easy with a drill press, but it is hard with a hand drill. I ended up over-drilling holes, then covering bolts in Vaseline and curing in place with micro-balloon thickened epoxy. If you do this, cover the wing and fin with plastic wrap and plan on discarding bolts afterwards.
4.) attach mast to fuse.
I made the fuse with a cutout for the mast that I very carefully wrapped carbon around, and then glued the mast into the cutout and cured it. This was a pain in the ass, so next time, I think I'd just carbon the whole fuse and glue the mast to it, maybe with screws through fuse to hold mast in place while glue dried. Either way, make sure the mast is in-line with the inserts. I put the front wing on and let glue dry while mast was held in place with 2 chairs.
5.) layup the mast.
I put about three short strips of carbon around fuse and a couple inches up each side of the mast and main mast layup on top of this, the main mast layup also descended down onto fuse (I tried to wrap opposite ends around fuse and onto each other, but this didn't work). Main mast layup is 6 layers- uni, triaxial, uni, triaxial, uni, triaxial. Triaxial is with 0 degree fibers along length of mast, in line with uni. I laid them all out on a piece of parchment paper, then tried to wet this out. Do not do this, wet out one layer at a time, squeegee, and cover with next layer. You will now have 6 layers of wet carbon on a piece of parchment, use a squeegee to get out as much resin as you can, then wrap this around leading edge of mast. Carbon should extend a bit past trailing edge, you'll trim this later. Vacuum bag this. Make sure to cover any sharp parts of fuse with something soft or the bag will get holes. I used peel ply and bleeder cloth, and this sucks some more resin out, but you don't need it. If you get to this when the resin is cured, but still a bit green, you can trim trailing edge with a utility knife. Otherwise you need a dremmel or hack saw. With this epoxy, it seems about 12 hours was ok to cut with a knife (but I'm not sure what temperature my apartment was at). My mast ended up about 13mm thick, so thinner than stock.
6.) Attach plate to mast.
I wrapped a piece of balsa with a few layers of carbon, and cured with books piled on top (and parchment paper to release resin). I then used epoxy thickened with micro balloons to a peanut butter consistency to attach plate to mast. A 90 degree angle between plate and mast is tough to wrap and also probably quite weak, so try to get the paste to soften this angle a bit. Allow this to cure, making sure the angle to mast is right. I used to chairs to hold mast in position. Once it is cured, wrap a bunch of carbon along plate and a few inches up the mast. I tried to stagger the ends of these to prevent a weak point in mast. Some of the carbon went all the way around plate, some went just on the top side of plate. This was vacuum bagged. Mine ended up pretty ugly, but good enough. Once cured, I drilled holes through plate and soaked exposed balsa with some epoxy.
7.) let it cure completely, at least 48 hours, in a hot car if it is summer time. Now beat the shit out of it. I never fully tried to break mine, but I was pretty rough on it before riding it. The weak points will be mast-plate, mast-fuse, and fuse-front wing. Step on the plate and yank front wing side to side, put all your weight on the front wing, whack it a good few times. If it breaks- great news, you saved yourself a pair of wings! My first one broke at wing inserts, and the second one was way better.
8.) make it smooth and pretty.
I skipped this step. Mine is rough and ugly as sin. The mast is kind of foil-shaped and kind of symmetrical. It doesn't seem to matter in the least. I wet sanded for about 5 minutes with 60 grit sand paper and that was it. I figured it would feel draggy and sing, but doesn't. If anything, it rides smoother and quieter than stock aluminum, probably because the mast and fuselage are both thinner. Again, I only free ride, maybe max speed ever of 25 knots.
Notes- the hard parts are the inserts and the joints, everything else is pretty easy. Do not dry sand carbon. Carbon splinters, either cured or dry, are terrible. Clean up carefully immediately after working, especially if you are working in your living room, and especially if your wife uses this area for yoga. If you use Vaseline for epoxy release, try to get off as much excess as you can, you don't need much and you don't want it on parts to be glassed. You will never get all the epoxy off of the bolts, so use cheap bolts you can discard at the end. 3/4" biaxial sleeve was a tight fit, I'd use 1" next time. I tried biaxial sleeve for the mast (3" just fits over a 4.5 inch chord), it doesn't work well on trailing edge. 32" mast is too short in my opinion. The mast flexes a little bit, but the most flex comes in the joints. I don't think it is quite as stiff as the stock aluminum set up, but I can not feel this while riding, and it is quite stiff. Finally, do NOT do this to save money. This is a hobby. If you want a carbon foil but can't afford one, get a minimum wage night shift at McDonald's until you have enough money for the most expensive foil you can find, you will be on the water sooner. I'm sure someone with a proper work shop and proper composite experience would do this faster, but if you read this far, you probably have about the experience and work setup I had, and it will take much longer than you think. I really enjoyed making this project, but I'm not keen to make another soon, my next project will probably be a pocket board.