Rule 32
(b) The term "short blast" means a blast of about one second duration.
(c) The term "prolonged blast" means a blast of from four to six seconds duration
The signal indicates that the vessel behind you wishes to overtake you on your port side
If you agree 1 prolonged blast one short blast one prolonged blast one short blast
If you disagree rule 34(d) (Manoeuvring and warning signals), if a vessel (vessel B) fails to understand the intentions or actions of the other vessel (vessel A), or is in doubt whether sufficient action is being taken by the other vessel (vessel A) to avoid collision, the vessel in doubt (vessel B) shall immediately indicate such doubt by giving at least five short and rapid blasts on the whistle.
Main rules being applied are
Rule 9 (Narrow channels)
Rule 13 (Overtaking)
Rule 34 (Manoeuvring and warning signals)
Also being considered are
Rule 7 (Risk of collision)
Rule 8 (Action to avoid collision)
Arc of light is rule 21 (Definitions)
Intensity of lights is rule 22 (Visibility of lights). Our vessel is 13.2m in length therefore the intensity should be such that it can be seen from a distance of not less than 2 miles.