def residual_resistance_coef(slenderness, prismatic_coef, froude_number):
Cr = cr(slenderness, prismatic_coef, froude_number)<EOL>if math.isnan(Cr):<EOL><INDENT>Cr = cr_nearest(slenderness, prismatic_coef, froude_number)<EOL><DEDENT>return Cr<EOL>
Residual resistance coefficient estimation from slenderness function, prismatic coefficient and Froude number.

:param slenderness: Slenderness coefficient dimensionless :math:`L/(∇^{1/3})` where L is length of ship, ∇ is displacement
:param prismatic_coef: Prismatic coefficient dimensionless :math:`∇/(L\cdot A_m)` where L is length of ship, ∇ is displacement Am is midsection area of the ship
:param froude_number: Froude number of the ship dimensionless 
:return: Residual resistance of the ship