Section 34(c) in Prevention Of Collision On National Waterways Regulations, 2002
(c)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 collission the vessel in doubt shall immediately indicated such doubt 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.
