#COLREGs – Rules 33-34

What Does Rule 34 Say?

Rule 34, Section A-i, says: “When power-driven vessels are in sight of one another and meeting or crossing at a distance within half a mile of each other, each vessel underway, when maneuvering as authorized or required by these Rules shall indicate that maneuver by the following signals on her whistle: 

  • one short blast to mean ‘I intend to leave you on my port side’;
  • two short blasts to mean ‘I intend to leave you on my starboard side’;
  • three short blasts to mean ‘I am operating astern propulsion’.”

Section A-ii goes on to say that the opposing vessel is either to return the same signal (safe to proceed) or issue the “in doubt#” signal, i.e., 5 short blasts (No go! May be danger ahead for YOU!)  This is the essence between the International Rules – which require no response from the opposing vessel (unless danger is ahead) – and the Inland Rules which seek to ensure that the opposing vessel understands your signal.  Given the close quarters of Inland conditions, you can readily understand the seamanship reasons for this double-check.  Rule 34, Section B, goes on to say that you can supplement your whistle signals with corresponding light signals.

Rule 34, Section C-i, says: “When in sight of one another, a power-driven vessel intending to overtake another power-driven vessel shall indicate her intention by the following signals on her whistle:

  • one short blast to mean ‘I intend to overtake you on your starboard side’;
  • two short blasts to mean ‘I intend to overtake you on your port side’.”

Section C-ii, like A-ii, goes on to say that the power-driven vessel about to be overtaken shall, if in agreement, sound a similar signal.  If in doubt she shall sound the “in doubt” signal.

Rule 34, Section E, requires that 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.  Rule 34, Section F, requires when a power-driven vessel is leaving a dock or berth, she shall sound one prolonged blast.

What Does This All Mean?

If you aren’t issuing all these sound signals, are you in violation of the Rules of Navigation?  After all, all these rules and sections use the word “shall” again and again – and “shall” means “must!”  But can you imagine all the boats in bay or harbor constantly issuing these sound signals?  I can’t… But what about when conditions deteriorate?  Wouldn’t it be great to know how to signal intent – of course.

Of note, Rule 34, Section F, gives us a modernized “out” – “A vessel that reaches agreement with another vessel in a head-on, crossing, or overtaking situation, as for example, by using the radiotelephone as prescribed by the Vessel Bridge-to-Bridge Radiotelephone Act (85 Stat. 164; 33 U.S.C. 1201 et seq.), is not obliged to sound the whistle signals prescribed by this Rule, but may do so.  If agreement is not reached, then whistle signals shall be exchanged in a timely manner and shall prevail.”

If you are trailing the “head boat” full of paying fishermen and you want to pass her on your way to sea, here is how you’d do it in a professional fashion:  

  • “Motor Vessel Rosie, ahead, this is the Motor Vessel ‘Charlie’ on your stern.”
  • “Charlie, this is Rosie.  Pass your traffic.”
  • “Rosie, I’d like to pass you on two whistles.”
  • “Charlie, this is Rosie.  There is up-bound traffic passing me to port.  I suggest you pass me on one whistle.”
  • “Rosie, this is Charlie.  Thank you, skipper.  Passing you on one whistle.  Initiating power-up.  Have a great day fishing.  Motor Vessel Charlie, out.”

What just happened?  In #1, Charlie gets Rosie’s attention – like she would have by issuing 2 short blasts on her whistle as required by Rule 34, Section C-i-2.  #4 is Charlie issuing 5 or more short "in doubt" blasts – danger ahead for YOU – don’t go!  Rosie goes one step further in suggesting a safe passage – on one whistle or as prescribed in 34-C-i-1.  And Charlie does, increasing speed to do so…  Using more modern technology – a radio – and using the language of the sea…

What Does Rule 33 Say?

Rule 33, Section A, says a vessel of 12 (about 40’) meters or more in length shall be provided with a whistle, a vessel of 20 (about 66’) meters or more in length shall be provided with a bell in addition to a whistle, and a vessel of 100 meters (over 300’) or more in length shall, in addition be provided with a gong, the tone and sound of which cannot be confused with that of the bell. The whistle, bell and gong shall comply with the specifications in Annex III to these Regulations. The bell or gong or both may be replaced by other equipment having the same respective sound characteristics, provided that manual sounding of the prescribed signals shall always be possible.  Section B says that vessels under 12 meters is not obliged to carry the “sound-signaling appliances” prescribed in 33-A – but still must have some “other means of making an efficient sound signal.”  So, even you, Bunky, with the 13’ skiff, have to be able to communicate like the battle wagons!


# In January 2018, the USCG dropped the long-used term “danger signal” and replaced it with the term “in doubt.”  It covers more ground, as it were.  With thanks to fellow USCG Auxiliarist and fellow licensed Master, Alan Karpas, for pointing out the change in language.