(1)Single vessel when vessels are in-sight of one another a mechanically propelled vessel underway, when maneuvering as authorized or required by these regulations, shall indicate her intentions by the following signals on her whistle.(a)One short blast (a blast of about 1 second duration) to indicate."I am altering my course to starboard"(b)Two short blasts to indicate " I am altering course to port"(c)Three short blasts to indicate "I am operating stern propulsion."(2)Overtaking vessels(a)Two prolonged blasts (blast of about 4 to 6 seconds duration each) followed by one short blast to indicate " I intend to over take you on your starboard side."(b)Two prolonged blasts followed by two short blasts to indicate "I intend to over take you on your port side."(c)A vessel being overtaken shall indicate her agreement by the following signals or her whistle; one prolonged, one short, one prolonged, one short blast, on that order, if in doubt she may sound signals prescribed in paragraph (3)(3)When in doubt - When vessels in sight of one another are approaching each other and from any cause either vessel fails to understand the intentions or actions of the other or is in doubt whether sufficient action is being taken by the other to avoid collision, the vessel in doubt shall immediately indicate such doubt by giving at least 5 short and rapid blasts on the whistle, the signal may be supplemented by a light signal of at least 5 short and rapid flashes.(4)At bends - A vessel nearing bend or an area of a channel where other vessels may be obscured, shall sound one prolonged blast, such signal shall be answered with a prolonged blast by any approaching vessel.
