What is the issue?
In busy waterways large vessels use sound signals to notify nearby boats of their intentions.
Why address this?
If you are unaware of the signal communications it may become problematic in busy waterways and place your vessel and surrounding craft in jeopardy.
How to address this?
Print out the 'Sound signals used by commercial shipping' summarised in figure 1 and have it handy when in busy waterways.
In a little more detail, marine regulations specify that a vessel of twelve metres or more in length must have sound signalling capabilities. A vessel of less than twelve metres is not obliged to carry sound signalling equipment as long as they are enabled with some other means of signalling.
Sound signals are of two kinds a short blast or a prolonged blast:
A short blast = a blast of about one second's duration.
A prolonged blast = a blast of from four to six seconds' duration.
Sound signals are used when vessels are in sight of one another and meeting or crossing within half a mile of each other. The following signals indicate:
One short blast = "I intend to leave you on my port side"
Two short blasts = "I intend to leave you on my starboard side"
Three short blasts = "I am operating astern propulsion"
Or a vessel sounds its overtaking intention:
One short blast = "I intend to overtake you on your starboard side"
Two short = "I intend to overtake you on your port side"
If in agreement with these manoeuvres you should acknowledge by repeating the signal back to the sender.
If by contrast you doubt the safety of the proposed manoeuvre, or you doubt whether sufficient action is being taken to avoid collision, you should signal that their intentions are unclear otherwise know as the ''danger signal'':
Five short and rapid blasts = ''danger signal''
Lights have the same sequence with the duration of each flash at about one second. The light should be an all-round white or yellow that is visible for about two miles synchronized with a sound signal.
The other times that a vessel is likely to use a sound signal is when they are nearing a bend or an area of a channel or fairway where other vessels may be obscured from their view. At these times they sound a single prolonged blast. This signal should be answered with a prolonged blast to indicate your presence. When a power-driven vessel is leaving a dock or berth they also sound one prolonged blast.
Michael Harpur, Yacht Obsession.