Foil Utilities, Cont'd

Giving you an idea of some of the forces at work (and how strong your foils have to be)

Calculate Righting Moment


Very simple approach - neglects righting moment of hull itself,
and bases all calculations on 'W' - the half-width of the hull.

half-width of hull:
crew weight height
1
2
3
Righting moment:

Assumes: 

Why should you care about righting moment?  This is one factor in determining the maximum lift your centerboard needs to generate, and how stiff and strong it should be. 

You may wish to multiply the result by a weighting factor > 1 to account for crew dynamics and pumping.

Calculate Lift

Provides an estimate of the lift generated by your foil.
Velocity Planform area (wetted)
Coefficient of Lift Fluid density
slugs/ft3
Calculated Lift:

Sample Coefficients of Lift

These are to be used only as general guidelines - coefficient of lift varies according to aspect ratio (and other planform factors) and Reynolds number, to name just some of the variables.

CL

 Description
1.50  NACA0012 at angle of attack of 15 degrees (max before it stalls)
0.25  NACA0012 at angle of attack of 3 degrees (typical leeway angle upwind)
0.80  NACA0009 at angle of attack of 10 degrees (max before it stalls)
0.30  NACA0009 at angle of attack of 3 degrees

For maximum lift generated by your centerboard, think in terms of hullspeed upwind (if you're planing, you're probably also retracting the centerboard).   For maximum lift generated by your rudder, think in terms of hgh steering angles at maximum speed downwind.

Multiply the lift generated by your centerboard by one half of its submerged length, and determine if that exceeds the righting moment  that your crew can generate.


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Revised: March 07, 2004