Reynolds number (Re)

The Reynolds number $Re = V L / \nu$ is the dimensionless ratio of inertial to viscous forces, with $\nu$ the kinematic viscosity (about $1.19 \times 10^{-6}$ m^2/s for 15 C seawater). It governs the frictional (viscous) part of resistance and the state of the boundary layer. Full-scale ship $Re$ reaches $10^8$ to $10^9$, far above any towing-tank model, which is exactly why friction cannot be scaled by Froude’s law and must be split off with a friction line.