The resistant force D of a sea-going ship is due to wave-making and viscous drag, and is a function of velocity V, ship length L, width b, seawater density $\rho$, viscosity $\mu$ [in kg/(m$\cdot$s)], and gravitational acceleration g. Use $\rho$, V and L as repeating variables to rewrite the functional relationship in terms of dimensionless $\Pi$ groups.