Whistle sound signals at sea come in two varieties, according to the International Regulations for Preventing Collisions at Sea (IRPCS): a short blast and a prolonged blast used for maneuvering and warning.
- The short blast means a blast of about one second’s duration,
- while a prolonged blast is four to six seconds long.
Think of these two different types of blasts as options to use in combinations.
Rule 34 of COLREGS describes maneuvering and warning signals for vessels.
In international waters, when a power driven vessel is underway and in sight of other boats and ships, the following whistles indicate its maneuvers …
- One short blast: I am altering my course to starboard.
- Two short blasts: I am altering my course to port.
- Three short blasts: I am operating astern propulsion.
Operating astern propulsion does not mean that the vessel is already making way in reverse. It is an alert that the thrust has been reversed and the vessel expects to be going backward soon. The heavier the vessel, the longer it will take to gather sternway.
FIVE or more short blasts are used when vessels are approaching in sight of one another and the intentions or actions of one of the vessels is not understood by the other. Another reason to use this signal is when in doubt that a potential collision will be avoided. If danger lurks, think of signaling at least ‘five short and rapid blasts on the whistle’ to the other vessel.
One additional warning signal is covered in this rule …
A vessel nearing a bend or an area of a channel or fairway where other vessels may be obscured by an intervening obstruction shall sound one prolonged blast. Such signal shall be answered with a prolonged blast by any approaching vessel that may be within hearing around the bend or behind the intervening obstruction.
If you have ever driven the road to Hana on Maui, it is the exact same tactic you use with your car’s horn.
The international version of Rules of the Road doesn’t require that the port or starboard maneuvering signals be answered.
However, the U.S. Inland Rules do make provisions for agreement by the other vessel. For maneuvering port or starboard, the IRPCS is understood to mean that a powerboat unilaterally acts (I am altering my course), while the Inland Rules of the Road require that a powerboat ask for permission (I intend to alter my course).
When overtaking in a narrow channel or fairway, the International Navigation Rules do require that the overtaking vessel wait for agreement by the vessel being overtaken before it commits to safe passing from the stern. The overtaking yacht will sound the following signals …
- Two prolonged blasts followed by one short blast: I intend to overtake you on your starboard side.
- Two prolonged blasts followed by two short blasts: I intend to overtake you on your port side.
The overtaken yacht shall indicate her agreement by the following signal on her whistle …
- One prolonged, one short, one prolonged and one short blast, in that order.
If in doubt, the overtaken yacht can sound the danger signal. The U.S. Inland Rules for overtaking in a narrow channel are similar in concept, but not identical in signals, to the international version.
What constitutes narrow channels? The IRPCS does not contain a specific definition, but admiralty law judges have ruled and local harbor pilots generally agree that it is a buoyed channel. In addition to the width of the channel, the overall size of the vessels in the fairway and their maneuverability must also be taken into account.
The next article in this series will review sound signals for vessels operating in conditions of restricted visibility.