Rule 33: the sound signal equipment you must carry.

What does COLREGs Rule 33 say?

Rule 33(a) sets the equipment by length. A vessel of 12 metres or more carries a whistle. At 20 metres or more she carries a bell as well. At 100 metres or more she also carries a gong, whose tone and sound 'cannot be confused with that of the bell'. All three must meet Annex III.

Rule 33(b) lets a vessel under 12 metres go without them — but then she needs 'some other means of making an efficient sound signal'.

What equipment does each size of vessel need?

Less than 12 metres: no whistle, bell or gong required — but if she does not carry them, some other means of making an efficient sound signal (Rule 33(b)).

12 metres or more, but less than 20 metres: a whistle (Rule 33(a)).

20 metres or more, but less than 100 metres: a whistle and a bell (Rule 33(a)).

100 metres or more: a whistle, a bell and a gong (Rule 33(a)).

Length means length overall (Rule 3(j)).

Can the bell or gong be electronic?

Yes, on a condition. Rule 33(a) allows the bell or gong, or both, to be replaced by other equipment with the same sound characteristics, provided that 'manual sounding of the prescribed signals' is always possible. Annex III 2(b) makes the same point about the bell: where practicable a power-driven striker is recommended for a constant force, but manual operation must be possible.

What does a boat under 12 metres need?

Under Rule 33(b), either the appliances in 33(a) or some other means of making an efficient sound signal. The rule does not define 'efficient'. In our view it means loud enough to be heard by the vessels you need to warn, and able to make the blasts that Rules 34 and 35 call for — a horn does that.

Does a 15-metre yacht need a bell?

No. Rule 33(a) requires a bell from 20 metres; at 15 metres she needs a whistle only.

Rule 35 lines up with this. Under Rule 35(i), a vessel of 12 metres or more but less than 20 metres is not obliged to give the bell signals for a vessel at anchor (35(g)) or aground (35(h)). If she does not, she must make some other efficient sound signal at intervals of not more than 2 minutes.

And under 12 metres?

Rule 35(j): a vessel of less than 12 metres is not obliged to give the Rule 35 signals at all, but if she does not, she must make some other efficient sound signal at intervals of not more than 2 minutes. Not having to give the prescribed signals is not the same as having nothing to sound.

What does Annex III require of the bell and gong?

Annex III 2(a): a sound pressure level of not less than 110 dB at one metre. Annex III 2(b): made of corrosion-resistant material and designed to give a clear tone; for a vessel of 20 metres or more, the mouth of the bell is not less than 300 mm across; and the striker's mass is not less than 3% of the bell's.

Annex III 3(a) leaves approval of the construction, performance and installation of sound signal appliances to the flag state.

What about the whistle?

Annex III sets limits for its fundamental frequency by length — lower bands for bigger vessels, though they overlap — and gives audibility ranges for information, from 2 nautical miles for a vessel of 200 metres or more down to 0.5 under 20. The figures are on the Rule 32 page.

Why does a vessel of 100 metres or more need a gong?

Because of Rule 35(g). At anchor in restricted visibility, a vessel of 100 metres or more rings the bell in the forepart and, immediately after, sounds the gong rapidly for about five seconds in the after part. A bell followed at once by a gong tells a listener she is 100 metres or more in length and at anchor — or aground, if the rapid ringing has three separate strokes before and after it (35(h)). In our view, that is why the gong must not be confusable with the bell.

How might Rule 33 come up in an MCA oral?

It may come up as a question about your own vessel, then a fog question. Examples of the kind of question to be ready for:

“What sound signalling equipment must a 24-metre yacht carry?”

“What about her 6-metre tender?”

“Can the bell be replaced by an electronic system?”

“Why does a vessel of 100 metres or more carry a gong?”

Where do candidates go wrong on Rule 33?

The common slips: putting the bell at 12 metres instead of 20; forgetting the gong at 100 metres, or that it must not sound like the bell; leaving out the condition that manual sounding must always be possible; and saying a boat under 12 metres needs nothing, when she needs some other means of making an efficient sound signal.