Zephyr Foil Build Log. Stage 1: CAD, Design Summary and Build Plan

Hi All,

I am about to commence my second build. I have completely redone the design based on my past shortcomings, and with my new workspace I have much more expanded building capabilities. I will update this post as I go. I look forward to your feedback!

CAD snap-shoots:



The Board:

165cm Long
Hatch space: 57cmx29cmx7.5cm
Hatch lid: DPI marine Flush series 13x24"

I will be carving the EPS foam core on my CNC router. Due to machine size and EPS foam availability in my area (Ontario, Can). I will use twelve 2x14x22" foam blocks and 6 1x14x22" blocks. 1lbs density. and glued together with EPS foam glue. I designed the board so that the draft angles of all the blocks will only require machining on one side.

Foil mount:
3 layers of plywood cut to fit into the foam core with aluminum rods that I can drill and tape for my foil mount. I will epoxy this into the foam and there will be a few layers of carbon between the 2" foam layers.
The whole board will be covered in carbon and glass.

Mast and Mast Plate:
Slingshot 71cm


Front wing is about 1500cm^2 loosely based on the slingshot hoverglide wings. 80cm wide and 25cm long. NACA 2412 profile.
Rear wing 350cm^2 and 40cm wide.
These will be all carbon made in a close mold. Still working on the build process.

I debated long and hard about what to do here, there doesn’t seem to be many options. I decided to go with “HGL-Tech” motor, esc, and controller, because it is an all in one package, including propeller, and I have seen it be used successfully in other builds.

For batteries I am using 3 4s cells set up in 12s. 18amp hours. https://www.amazon.ca/gp/product/B07F19S988/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I have them stored in a waterproof computer hardcase: https://www.pelican.com/ca/en/product/cases/laptop-case/hardback/1075


Carved from a piece of 1" aluminum hex rod. Length undecided at the moment.

Motor Mount:

I will be using 19mm HPDE plastic as a mounting plate for the motor, and clamped to the mast with bolts through an HPDE Piece fit to the mast.

The fairings will be made out of carbon


I am moderately worried about getting my toes cut off by the prop, so this duct is mostly for safety. I do not have the fluids experience to design a thrust increasing duct, this one will only serve to create drag, but may save my toes.
Right now the plan is to 3D print it from nylon Carbon filament, then skin it in carbon until it is strong enough. Will require lots of sanding and fairing but I think will be the easiest way to build it.

I have future plans for a folding prop, water-cooling, and a brain to motor the systems and throttle response curve. But these will not be included in the Mark 1 version
The build starts next weekend with the board. It is a few hours of machining for all the foam blocks, then they will be glued together and skinned in several coats. I will respond to this post with photos of the build process. I look forward to hearing your feedback.



Beautiful looking design! One question related to the " stern" of the hull. Can se that it is rounded up so to say. Considering the take off speed for flying and also possible un intended touch down in water when flying, would it not be less drag to have the “transom” sharp, like the transition from the bottom to the transom on a planning hull boat? Never foiled so can not say i know anything about that sorry my question :smiley: but typically when exceeding hull speed(that is very low on this length) a sharp shape might let go the water easier?

I was always looking for cad model like this to print it in small and have it on my office desk to impress my colleagues. Is there any chance I could get it? Shape is enough without all of the compartment. I would not be able to draw this by myself…

Your help is highly appreciated

1 Like

Nice plan. I’m at the same stage with mine and I plan to use similar parts. I’ll be watching close for updates.

What kind of ride time are you anticipating with the 18 ah battery? 20-30 min?

I can confirm it requires LOTS of awkward sanding :tired_face:, I’m in the middle of doing mine and my thumbs are sore and cracked from all the sanding.
It does look good though when complete.

Will the nylon carbon filament not be strong enough as it is?.

Good to know I’m not the only one willing to suffer through!
Honestly I’m a little disappointed with the quality of the prints and the strength of the nylon. I’m sure there are adjustments to be made to the print settings but the parts haven’t been very rigid.
Even if it were strong enough, the nylon filament is very hydrophilic, so it would need to be sealed with epoxy and then sanded anyways.

Here is some good info on transom design for hydrofoil boards.
The foils should be lifting the board out of the water well before reaching planning speed, so instead you need some rocker at the back for pumping.

1 Like

I think 20-30minutes sounds about right. I have a bit of additional space in my battery box to stuff a few more amp hours in, and hopefully get to 40minutes.

Printed my duct in ASA-X at the time, printed the (straight) struts with a hole inside and epoxied 3mm cfk rods inside. Then added a layer of cfk only on the outside of the duct, easy to sand.
See here: Daniels geared inflatable (slowly built)

Although I don’t use this duct anymore, it was solid enough to not deform under load, it worked quit well.

1 Like

Thanks! That is a good idea, will be much easy to sand that way.

Nice , I suppose depth is 7,5cm ? You took account of the thickness of the hatch ( looks like 20mm) not much room for the battery , no ?

Good idea, it’s getting between the spokes that’s a b**ch. Mine has 6 but wish I had opted for 3 or 4 instead :roll_eyes:, would increase efficiency too.

OK, thanks, that make sense, sure if rocker it will be easier to pump and that hull shape will also tend to lift the bow(as long as it is in the water) . I was just thinking a E driven foil would have little different requirements but as said, I have no own experience at all so thanks for good info!

Yes, 7.5cm deep, thanks for that, I corrected the post. It should all fit. I did a mock layout the other day. I am not leaving much room for expansion, so hopefully the battery life I get will be good enough.

When choosing tap shape, please consider the usage of the board. Where most non powered surf-foils prefer B & C type to “kick of from waves”.
I consider an E-foil an constant flying vehicle ( I do not ride extreme waves). Due to that we want the easiest take off requiring least amount of power. I would argue that Tail D provides the easiest water separation and Tail C the hardest since water will follow the bend surface and create downforce. It feels like board is sucked into the water and then it pop ups to flight quite violently.

I ride DYI inflatable, so naturally C-type and it requires 4kw to lift, which is no big deal when only lifting once per session, so I have not cared.
I have ridden some Fliteboard Inflatables though and there is a reason it transitions super smooth to flight. They have added a sharp 90* edge to the back to mimic the D-shape.

Easy for beginner to learn, then choose D for Foil. My 5 cents.

1 Like

Could you please send me the drawings?

I will start to share my CAD as I complete the components. Until something is built, the cad is a work in progress.