Discussion in 'Boat Design' started by Sassriverrat, Oct 9, 2017.

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### SassriverratJunior Member

Good Afternoon-

Looking to put some horizontal "fins" on a bow. I assume these would have applicable hydrofoil lift characteristics if they were submersed but I was wondering if anyone had any simple formulas for calculating the lifting force they generate based on angle of attack, square footage (or inches), and the basis that these are designed to generate lift like a ski- by coming to the surface and planing.

Thanks,
Austen

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### tom28571Senior Member

I will not presume to give you a simple formula to determine lift of your foils but the factors affecting the answer are fairly simple. Lift will vary proportionately to the area, trim angle and aspect ratio (beam/length) of the foil as well as the square of the velocity. As your foils will probably not be the prime determinate of the attitude of the boat, trim angle and immersion will vary depending on displacement and pitching of the hull in waves. I've not done this relative to attached foils to a hull but know that others have, especially on multihull powerboats. I think it was covered in an old issue of Professional Boatbuilder. Probably some experimentation on your boat will be needed in any event, regardless of calculations.

3. Joined: Sep 2017
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### SassriverratJunior Member

Thanks for the reply. I've seen talk about it with catamarans but I guess the formula I was seeking, and maybe I didn't ask correctly, is a loading one for riding the surface. These are designed to ride on the surface like skis, not under the surface, so I didn't know what formula might be used for say, water skis. Thanks!

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### DCockeySenior Member

"Hydrofoils" do not usually ride on the surface. Rather they are either fully or partially submerged. For foils "designed to ride on the surface like skis" planing boat theory and analysis would be relevant. Savitsky's method may be applicable.

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### SassriverratJunior Member

Yes agreed. My poor choice in wording. Let me go try working some magic.

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### wet feetSenior Member

I would need to be very sure about the lack of flotsam in my boating area before grafting fins onto any bow.I would also need to be convinced that hitting something wouldn't leave me with a hole in the boat if they were to be wrenched off.The engineering required to be certain of this might not be a trivial matter,but then neither are the consequences of a hole in the boat.

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### boatbuilder41Senior Member

Thids helped me in many ways.

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