As vsl in restricted visibility we can positively use sound signals as per rule no 35 while making way 1 prolonged.
Vsl in RV, port bow vsl crosing as per rule no 19 clearly restrict to a/c to port for avsl fwd of her beam otherthan for a vsl being overtaking, only option is left us to reduce speed to minimum at which she can be kept on her course.So overtaking vsl is overting from stbd quarter ,if we reduce speed , overtaking vsl wil overtake our vsl in shortest period of time.