Motivation

Last Saturday my friend Gonzalo Bandeira and I were bored and decided to meet for a round of Pitch & Putt. Being the golfer he is, his mind was set elsewhere. He soon started “pitching” the idea of starting to learn how to ride a hydrofoil with our kites. A quick search on Google revealed that a full set of hydrofoil + board would cost around 1500€, a price we weren’t willing to pay. However, he wasn’t deterred. We hadn’t reached the fifth hole and he was already looking for second hand options, and soon turned into DIY solutions. We started discussing how it could be done. Needless to say, It wasn’t the best round of golf we have ever played

We have been talking about it over Whatsapp quite a lot, on thingiverse, there are several we liked such as this one or this other. Unofficially we have assigned roles, Gonzalo will be the manufacturing engineer, while I will be the design engineer. This is going to be a complicated project and I believe we won’t get it right on the first go (Here my colleague disagrees). Besides,from people we have spoken with, it turns out FoilBoarding is nothing like regular kiteboarding. Great. So we are building something we don’t know if will work for a sport we do not know how to practice. Bring it on!

Materials – The Carbon Fiber problem

Checking commercially available foils, we have noticed most, if not all are built using carbon fiber. Therefore, we also started to look into ways of manufacturing carbon fiber reinforced plastics at home. As I have some experience with the later, I know how much equipment is needed for it to be done properly so I was (and still am) a bit worried about the final strength of the device. However, we reached a site called Clearwater foils. From what we can see, this guy manages to make the foil work just using wood and glass fiber. He uses a CNC router to get the airfoil shape of the wings, keeping a flat bottom, while the fuselage seems to be a 1″ square beam. For this version I managed to convince Gonzalo to go for glass fiber to avoid all the carbon hassle. For the rest of the foil we have agreed to use the full potential of 3D printing where possible. Large simple parts we will manufacture in wood while small and/or geometrically complex shapes will be 3d printed. The idea is to glass fiber everything once it is assembled to provide the strength required.

Front wing design

As we are really just looking for something that just works, we do not really care about optimization. There are infinite number of foil shapes, but doing a quick search, the EPPLER 817 comes up as a typical hydrofoil shape. Knowing some aerodynamics, and making an analogy, I can say that specially, the dynamics are really hard, so the best way to have a first version to then iterate on, is to copy someone else.

Looking on the internet, I’ve decided to set up on the liquid force “Happy foil”.The main reason being the claimed characteristics are what we are looking for, plus they have a published schematic of their dimensions.

Unfortunately I would like to design the front wing in CATIA V5 as its Generative Surface design module is really powerful and I know how to use it properly. However, two reasons stop me from doing so. First, CATIA is terribly expensive and they do not offer a free/trial license, second, I’m currently running a Mac. Therefore my only real option is Fusion360. On the upside, importing an image is really easy and creating a few control points for the splines is a breeze.

As it can be seen from the above image, the wingtips are not rounded as they are on the LiquidForce design. For the life of me, I couldn’t get Fusion360 to patch it. The main geometry is composed by five parallel planes which have the EPPLER 817 shape. I then created two guide splines to provide a smooth shape, and lastly created a loft feature between all the profiles. I haven’t made an interface between the wing and the fuselage as I expect have a custom part to change the angle of attack of the wing.

Manufacturing

To manufacture I had to slice the part into less than 200mm chunks. Also, to preserve strength Gonzalo and I agreed there should be an odd number of parts so the wing is not cut in half at the middle.

Unfortunately my printer doesn’t work too well at those heights and the chosen number of parts is 5. To align all the parts i’ve put an alignment hole in which a dowel pin can be inserted. Parts have been temporarily stuck using CA glue, just to hold until the first layer of epoxy and fiberglass is layed

I will keep posting with advances