Function vmg_to_waypoint_kn 

pub fn vmg_to_waypoint_kn(
    sog_kn: f64,
    cog_deg: f64,
    bearing_to_waypoint_deg: f64,
) -> f64

Speed made good directly towards a waypoint, knots.

Negative when the vessel is opening the range rather than closing it, which is the normal state on the wrong tack and must not be clamped away – a beat is a sequence of legs that individually look bad.