Another DIY Foil Project

[oldfartsuperdad]

Couldn't help it..the ex-Aero Engineer in me had to give this a try....gonna start with a Clearwater Kit - SUP specific and go from there.  Decided my L41 was a good candidate....generally I have as much fun building these projects as I do using them, but hoping the "using" works out more fun this time!  I think the wood core with glass makes an easy and sturdy construction and keep the cost down while I give this a try.  Planning to mount to parallel fin boxes with extra strengthening during installation into the board.  This will also give the ability to adjust the foil fore and aft a bit.  Still struggling with Mast Height cut - thinking to keep it shorter as I'm probably not going to be pumping around like the young kids.   I may be dreaming but who cares...mile long Puget Sound freighter waves and crap mushy days out at the beach....worth a go!

[PonoBill]

I used the standard kit and extended the foil. And I used carbon. Nice little kit. Saved me some time.

[SURFFOILS]

Oldfartsuperdad, what's your take on the relevance of NACA cross sections and how effective they are in hydrodynamics ? Thanks, Brett,

[oldfartsuperdad]

Hi Brett - NACA relevance is related to the amount of testing that has been done on these sections...a great deal of it.   6-series NACA cross sections have been looked at for foil use.  General hydrofoil design looks at a wing that does not have to undergo large variation in AoA.  I think one interesting and difficult design consideration for a "surfing" hydrofoil is the underlying circular wave flow that causes large AoA variation and subsequent flow separation from laminar.  At surfing speeds, we will not worry about cavitation which drives much of generic hydrofoil design.  The Speer H105 section may be worth a look - designed for lower Rn and reduced laminar separation at low speeds on sailing vessels.

On the other hand, I have seen videos of guys wake foiling on a flat plate piece of plywood!  I think when surfing, we will be so far away from any semblance of "steady state" that it may be harder to optimize for our use and there is likely a large variation in cross section that will prove adequate.

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that h105 section is very similar to what i am using, has massive lift at low speeds and regains laminar flow super quickly when you break the surface. apparently the big concave on the bottom makes pitch control more sensitive and there is also the extra drag from all that lift. also they hate speed, 3-8kts is perfect above 11kts you start to get big flow separation on the trailing sections

[PonoBill]

Now you tell me! I used something close to 2412 for the geezer foil. I expect almost no AOA variation since it's seven feet behind the front foil, which is the standard Clearwater foil wrapped in carbon. I think it's going to be draggy as hell but that's more a function of crappy execution rather than crappy design. I'm going to sand the dangerous edges off it and get it towed this week--unless the wind stays up and I'm too consumed with downwinding.

[oldfartsuperdad]

I left the Clearwater foil alone and just glassed it....more out of laziness and anxious to get building.  It's kind of a Clark Y flat bottom cross section...pretty thick.  Clearwater has some good vids of big guys wake foiling and kite foiling on this foil with homemade boards and the thing looks like it's working well so who knows....maybe I'll jack around with other sections on future models...fun stuff

[SURFFOILS]

Oldfartsuperdad,  the  Clearwater foils look basic but they get the job done.

Re-profiles,that's how I saw it too, you can make a foil that's super effective at a certain AOA but it's highly ineffective at a range of other angles. But that's based on lift through Bernoullian theory. Certainly the surfing environment will bring about different foil profiles and templates.

[surfcowboy]

Ok, glad this is heating up. Is the Clearwater made for SUP? He mentions a kit is coming but didn't respond to an email. Is this different from the kite foil?

Also, Pono, did you just put a metal plate on the bottom to extend it out?

[oldfartsuperdad]

He has a SUP specific kit....larger wing and lengthened fuselage.  He has tested it behind a boat and claims it works well.  As far as I know has not had it in the surf yet.  I had good communication from him...hopefully you will hear back soon.  The kit is very basic but well made...requires some glassing skills but not hard at all.

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this is my old foil section which was off an international 14 sailing skiff T rudder, this was trimable +/- AoA and works with the boat pitching and jumping all over the place so it would probably be not bad for surfing. sorta wish i kept it around until i got good enough to surf it instead of chopping the tips off for a new tail foil 

[blackeye]

(moved to the longest board thread)

[SURFFOILS]

That's interesting about a SUP specific ( larger)  foil. I've tried longer foil setups to mimic the board length but they're a bit slower to react when foiling. I know there's a direct ratio between total weight above the mast and foil area.

[surfcowboy]

Thx man. That's great to hear. Hmmm.. might be time to get one of these going. I have a 7'5" Simmons that's calling out for a foil mount.

[oldfartsuperdad]

Fini - just waiting for the board mod to install.  Elected for a shorter mast to help with the learning curve and will likely start another one soon with longer mast and may jack with the wing profile a bit.  Will post more when I get this thing installed and wet!