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Of Whistles, Bells and Gongs

The Royal Clangor

While the Rules of the Road do not make for stimulating bedtime reading, unless one is studying for their captain’s license, they do contain an interesting set of guidelines pertaining to the equipment for sound signals.

Masters of superyachts and ships of 100m (328ft) or more in length must make sure that their vessels have a whistle, a bell and a gong on board. According to the rules, bells and gongs are to be constructed of ‘corrosion-resistant material and designed to give a clear tone’. And for that gong, ‘the tone and sound cannot be confused with that of the bell’. A quick perusal of specialty ship chandler catalogues reveals that a brass signal gong, 0.5m in diameter with a hammer striker, can be had for under $300. Neither the bell nor the gong should be used as the signal for dinner being served.

For these large vessels, the whistle must be capable of being heard between 1.5 and two nautical miles away. Their loudness is measured in decibels (dB) when standing one meter away. A superyacht’s whistle will have a maximum intensity of 143 dB. Just how loud is that? The Decibel Equivalent Table, which equates loudness to ‘everyday’ sensations, rates 140 dB as the ‘threshold of pain’. Fortunately, the whistle on large vessels is just 1 dB below the intensity where the ‘nose itches due to hair vibrations’. Mariners will be thankful to learn that the International Regulations for Preventing Collisions at Sea (IRPCS) mandate that a whistle shall be placed as high as practicable on a vessel, in order to minimize hearing damage risk to personnel and that the sound pressure level of the vessel’s own signal at listening posts shall not exceed 110 dB. That’s just 10 dB lower than sitting in the front row at a rock concert.



What is a whistle, anyway? COLREGS define it as ‘any sound signaling appliance capable of producing the prescribed blasts’ and meeting the specified loudness laid out in the rules. Smaller recreational vessels, less than 20m (65.6ft) LOA, only need an audibility range of a half nautical mile. Whistles can be powered by steam, compressed air, electricity or one’s breath. On boats today, they are more commonly known as horns. By IRPCS definition, there are only two types of whistle blasts. A short blast—a blast of about one second duration, and a prolonged blast—a blast from four to six seconds duration.

The sound signals themselves are governed by two rules: Maneuvering and Warning Signals (Rule 34) and Sound Signals in Restricted Visibility (Rule 35). Rule 34 is expressly for power-driven vessels operating in sight of one another in meeting or crossing situations, while Rule 35 covers all power-driven and sailing vessels, day or night, in or near an area in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or other similar causes. Rule 35 further subdivides its prescribed signals into vessels that are underway and vessels that are not underway.


Steam whistle of the S/S Great Eastern built 1858
Steam whistle of the S/S Great Eastern built 1858


The definition of being underway is critical to deciding what sound signals to use for situations covered in Rule 35. COLREGS Rule 3 states: The word underway means that a vessel is not at anchor, or made fast to the shore, or aground. It’s succinct and to the point. And a vessel underway can have two states: underway making way and underway not making way. What is the difference? A power-driven vessel is considered not making way, when its transmission is in neutral and is stopped and making no way through the water. Of course, the vessel will still be subject to the motion of leeway, caused by any wind present, and drift, caused by any current.


Humble … but noisy
Humble … but noisy


In the next two articles in this series, the details of Rule 34 and Rule 35 will be explained. The Maneuvering and Warning Signals Rule covers course alterations, operation in a narrow channel, nearing an obscured bend and signals for dangerous situations. The Sound Signals in Restricted Visibility Rule highlights vessels underway, whether encumbered or not encumbered, and also when they are at anchor or aground.

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