Wake fraction (w)

The wake fraction $w = (V - V_A) / V$ is the fractional slowing of the flow into the propeller disk relative to ship speed $V$, so the advance velocity is $V_A = V (1 - w)$. It arises from the hull’s boundary layer, potential flow, and wave orbital velocities. Full single-screw hulls run $w \approx 0.25$ to $0.40$; twin-screw and fine forms are lower. The effective (Taylor) wake from self-propulsion tests differs from the nominal wake measured without the propeller.