Instructables

Make a Hydrofoil Blade from Windsurfer Fins

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Here's how to graft two windsurfer fins together to make the lifting part of a hydrofoil.
I lost the front hydrofoil blade from one of my Aquaskippers. This new blade works great as a replacement.
The foil section is just right for the purpose. And it's a really quick project.
The resulting blade is strong enough to use for an "air chair" or "sky ski" type hydrofoil, or any other weird hydrofoil project.
You can get windsurfer fins cheap at flea markets and yard sales.

You'll need the following:
Two windsurfer fins. Mine were each 9" long.
Epoxy. Not "5 minute epoxy". That stuff is crap.
Power Sander. I used a belt sander mostly.
Dust mask, safety glasses, clothing to keep the figerglass off your skin.
 
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Step 1: "Design" Your Hydrofoil

Picture of "Design" Your Hydrofoil
Pick out a couple of fins.
Like I said, you can get windsurfer fins cheap at flea markets and yard sales.
Unless you need them. Then they're expensive. So stock up now before you actually need them.

You'll notice an odd phenomenon, which is that no matter how many of them you have, you'll never have two that are the same.
So pick a couple that are close enough and live with it. The earth isn't symmetrical either or the ocean. It's not going to make any difference.

Step 2: "Analyze" Your Hydrofoil

Picture of "Analyze" Your Hydrofoil
Every windsurfer fin in the world uses the 63a010 foil section.
That's a 63010 section modified to take the concave out of the trailing edge of the foil.
If you find a fin with a different section it won't be enough different to matter.
If you want to see what some other sections might be, browse the foil catalog at UIUC. If you want to import the foil to the XFOIL simulator and make graphs to tack to your wall, here's some more info on that collection.

Your fins won't be exactly the same thickness, so get an idea where the center lines are and maybe mark the base with that. It won't matter if the centerlines are at different levels, but you'll want both fins to be at the same angle of attack.
bertus52x1117 days ago

Hi Tim,

I'm building a hydrofoil (www.wingbike.nl) and I'm struggling with the surface follower. I think mine is too large and a wrong shape. Would you mind sharing the dimensions of your surface follower? If you just give me the length and width, I'll figure out the rest (it's parabolic isn't it?).

That would be great.

ghatch2 months ago

If you're going to be using a sander and epoxy you might as well skip the use of old mismatched surfboard and sailboard fins and just make a wing out of plywood and glass over that. Single symmetrical arc and an even foil across both the leading and trailing edges. After you foil it you can finberglass over it.

The results of plywood+fiberglass will be at least 30% lighter than a solid fiberglass wing. A piece of 3/8" ply at the local hardware store is less than $10.

Within reason, a thicker foil creates more lift.

dome_head1 year ago
too bad spare parts are hard to get for aquaskippers. ingenious substitution. thanks!
FeedTheGrid5 years ago
Great knowledge to share. Thanks!
dacarls5 years ago
Why didn't you thicken the epoxy with cab-o-sil. Fills voids= strong like Bull.
yoshhash5 years ago
Tim....arguably instructables' most prolific inventor! There should be a special section just for this guy! I missed seeing your posts, I'm hoping that just means you were busy with new things. Nice mod! Please give us an update on the aquaskipper.......you must have added more features, gone longer distances......
SinAmos5 years ago
Classic. I'm thinking about showing how to mod an old sink into a glide-cam.
rimar20005 years ago
Tim never rests... The world needs more people like him.
You have that right, one person it would be interesting to meet.