Data for a VPP?

In winvpp, i think the residual drag is interpolated with a cubic polynomial curve. I agree that a linear interpolation is not correct. Particularly for Fn around 0.4 where the values change a lot.
LCBfpp is the distance in meters from the forward end of LWL
LCB is as presented in table 2, and should be negative a LCB of -3.28 means a LCBfpp of LWL/2+3.28/100*LWL.
What programming language are u using?

 

Oops. I may have the sign wrong. As a practical matter I don't think you'll find any hulls that actually have the LCB ahead of midships.

I'd say the taper ratio of the keel is 0.76, or a little less when you extrapolate the blade to the bottom of the bulb. The bulb is ignored for the purpose of defining the reference area.

 

I'm using C language.

I had already assumed that LCB would be the % values in table 2, but using a % value in residual drag equation does not seem to fit the logic used in other equations, which only uses non-dimensional parameter derived from actual measures (e.g. LCBfpp/LWL, VOLc^1/3 / LWL) and all the ratios (Cm, Cp) are in fractional from not in % (e.g. Cp=0.54 not 54%).

I have also checked the excel sheet that Nico has sent here and in it LCB is given in %, but with a wrong sign, but it is only used to calculate LCBfpp. Even more confusing....

Joakim

 

in my spreadsheet LCB is positive but i have changed the sign in the equation that computes the residual drag -*- = +

 

I think that the negative LCB in % is the way delft have described LCB from the start (for the last 25 years). With the LCBfpp/LWL they are probably moving to a form that is used most often used (ie. LCB=0.56).
% is just an easier way to write fractionnal number

 

Joakim

Did you try http://www.vacantisw.com for his foil lift/drag prediction software?

 

http://www.wb-sails.fi/news/SailPowerCalc/SailPowerCalc.htm

http://www.wb-sails.fi/news/SailPowerCalc/SailPowerCalc.htm

Aerodynamic calculations in this site seem a bit over-optimistic. Does anyone know where I can find a table of cl cd coeficients for a simple sail? Thanks in advance...