Regal 53 SC Owner's Manual page 46

NAVIGATION RULES
An overtaking boat is burdened, and is not the privileged craft, even
though it approaches the danger zone of the overtaken boat.
The overtaking boat fi rst signals with a single blast if that boat desires
to pass on the starboard side of the boat ahead, or a double blast if
passing to port. The overtaken craft responds with the same signal
if safe, or with the danger signal (5 short blasts or more) if unsafe.
The boat overtaking must not pass unless the appropriate signals are
sounded.
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Chapter 3