COLREGS ~ Part D ~ Sound and Light Signals (Rules 32-37)
Rule 32 gives definitions of whistle, short blast, and prolonged blast.
Rule 33 says vessels 12 metres or more in length should carry a whistle and a bell and vessels 100 metres or more in length should carry in addition a gong.
Rule 34 covers manoeuvring and warning signals, using whistle or lights.
Rule 35 covers sound signals to be used in restricted visibility.
Rule 36 covers signals to be used to attract attention.
Rule 37 covers distress signals.
Vessels are required to sound signals, to indicate their intention to maneuver, any time that they are in close quarters and risk of collision
exists. On inland waterways, intention/agreement signals are used. On international (offshore) waters, actual rudder
actions are signaled. Fortunately, although at first glance the two systems differ, both actually use the same effective meanings for signals.
Whistle signals may be supplemented by light signals using the same code.
* Short Blast - A blast of one to two seconds duration.
* Prolonged Blast - A blast of four to six seconds duration.
* Responding Signal, if understood & in agreement - Same as initial signal.
The following signals are the only ones to be used to signal a vessel's intentions (Inland Rules).
(i) Signal indicating intent to maneuver:
a. One short
blast to mean:
"I intend to leave you on my port side", or (when overtaking)
"I intend to overtake you on your starboard side".
b. Two short
blasts to mean:
"I intend to leave you on my starboard side", or (when overtaking)
"I intend to overtake you on your port side".
Double blast = Starboard pass - A double blast always means that you are turning (offshore) or will turn (inland waters) to port. This means that you will pass the other boat on your starboard side.
c. Three short
blasts to mean:
"I am operating astern propulsion" (backing up).
Danger or Doubt signal
d. Five or more short
and rapid blasts to mean:
“I don't understand or disagree with your intent.”
Each vessel should then slow or stop until signals for safe passing are sounded, understood and agreed to. The danger or doubt signal can also be used to tell another vessel that its action is dangerous. If a boat is backing up into an obstruction you would sound the danger signal to warn the operator.
(ii) Response signaling understanding & agreement:
Upon hearing the one or two blast signal of the other shall, if in agreement, sound the same whistle signal and take the steps necessary to effect a safe passing. If, however, from any cause, the vessel doubts the safety
of the proposed maneuver, she shall sound the danger signal specified in paragraph (d) of this Rule and each vessel shall take appropriate precautionary action until a safe passing agreement is made.
Note: If you are approaching exactly head-on, or very nearly so, the COLREGS prefer that you turn to starboard (single blast).