Hydofoil question

[stevebarrett]

Hi there,

I am hoping you can all help me resolve a debate I have been having with a friend. The basic question is...

"What limits the length of a hydrofoil?"

I am talking theoretically rather than practically speaking and for hydrofoils seen on dinghys such as international moths.

If the boat can produce enough lift to raise it out of the water by 30cm does it therefore also produce enough lift to raise it by 5m?

Do hydrofoils sit in a state of equilibrium under the water and if so what stops them lifting the boat higher i.e. so the foil is on the surface.

I'm sure i've not made myself very clear but I think i've got the rough idea across.

[Skippy]

The efficiency of the upper surface drops as the foil approaches about one chordlength below the water's surface, until at the water's surface, the foil's upper-surface efficiency is zero and the foil is planing. So yes, there is an equilibrium.

[stevebarrett]

Thanks for you answer..

What is a chordlength- does it differ dependent on the hydrofoil?

[Skippy]

The distance from the leading edge to the trailing edge.