Foil section? For foil board

Revintage,
You should try XFLR5 available on Sourceforges
For rookies like me XFOIL is a bit intimidating as it requires DOS commands
XFLR5 is a Window environment XFOIL, so much more user-friendly
You download the Selig UIUC database in the same folder, and things become very easy.
The price is some XFOIL functions are not available, like the Boundary Layer's H parameters.
Or I was unable to find them.
You have also airfoil-tools.com or something like that, which is running XFOIL too and nothing to download or unzip.
The learning curve is not that difficult for most of the XFOIL analysis, a bit more challenging when it comes to full-inverse method.
The time put at learning this software will be a great investment for your foil designer's life.
Best of luck
Erwan

 

Thanks for the tip Erwan, I have actually downloaded and installed XFLR5 and also spent a few hours digging into it. Had no problem to import my N12FLAT. Need more time though. About H, I think I have found it in the program. It was for that reason I initially wanted to try it. Will have to give it more time.
About N12FLAT I am already building a 100cm prototype foil for load testing.

 

I'm especially happy to have found this thread, especially for the useful replies. Thanks to one and all.

I'm considering a build that I hope would be able to fly a typically small light rowing dinghy as fast as is reasonable through a deadhead infested Georgia Strait.

I'm considering bringing two modes of propulsion: windsurfer style sails, and kites. A short, narrow rowing dinghy (8 ft LOA?) would require a VERY low take off speed (because of hull speed issues), but that seems to come with more drag. I would love to figure out how to calculate what the typical highest speed would be for a given foil.

Another option I'm considering is longer hulls in catamaran or trimaran form (16 ft LOA) (again with windsurfer sails and/or kites).

Basically I'm looking at a low wind option and a high wind option.

I'm imagining building a few test foils from wood (CNC milled perhaps?), without fibreglass or carbon to try to get the hydrodynamics sorted, and then predict how a fancier build would work by just removing a sandbag or two from a tow test. Is that the right approach?

Should the test foils have square ends? Or should I round them off?

Any recommended foil sections, and/or areas / aspect ratios for those two modes of operating?

 

@Christian Nally I suggest you read "hydrofoils: design build fly" by Ray Vellinga. He goes over pretty much all of the design process for a small hydrofoil without delving into too much math, and copies are cheap. I don't think a windsurf sail is a good idea for using on anything but a windsurfer. They are hard enough to use on a board that is designed around them, I can't imagine trying to foil a old style dinghy. I don't know enough about kites to comment on them.

making preliminary foils out of wood is not a good plan. The material, and therefore strength, is inextricably linked to what the best design is. A wood foil needs to be thicker in order to be strong enough, and will be higher drag at high speeds. If you want wood, fine, but design around it from the start and realize that if you swap materials you will need to design over again.

Planform is best elliptical or tapered, unless construction demands the foil to be rectangular. Vellinga goes into detail about foil section and lifting area and aspect ratio.

 

Thank you @ziper1221 much appreciated

 

Given the very low drag of a foiling Moth, and the much higher drag of a boat wide enough to row and only 8ft long, it seems hard to see how it would foil well.

The Moth also has the benefit of a very high righting moment and large but low drag sail, both of which it needs. When you pop up on the foil the apparent wind can increase dramatically.

I know an engineer with an excellent record as a sailor, designer and builder of high performance craft who gave up building his own foils because he couldn't make the junction of the mast and main foil strong enough in carbon at home, even vacuum bagging. If the junction is too bulky the drag is too high. It's hard to see a wooden foil working where carbon won't.

 

I've always heard that a well-faired junction will be much lower drag than a direct T-junction.