Rule 36: attracting another vessel's attention.

What does COLREGs Rule 36 say?

When a vessel needs to catch another vessel's attention, Rule 36 gives her two options. One is a light or sound signal, provided it cannot be confused with any 'signal authorized elsewhere in these Rules'. The other is her searchlight, aimed 'in the direction of the danger'. Whichever she uses must not embarrass any vessel.

Two further limits apply to lights. A light used for this must not be one that could be taken for a lighthouse, buoy, beacon or any other aid to navigation. And for the purposes of the rule, high-intensity intermittent or revolving lights, 'such as strobe lights', are to be avoided.

Does Rule 36 require a vessel to signal?

No — it says 'may'. It permits a vessel to signal when attention is needed and sets the conditions the signal must meet. Rule 36 itself does not oblige anyone to signal, and it does not prescribe a signal of its own: the rule names no particular pattern of flashes or blasts. As we read it, though, Rule 2's 'ordinary practice of seamen' may make a warning the right thing to do, and in the situation Rule 34(d) describes the doubt signal is required, not optional.

Who can use Rule 36?

Any vessel, whatever her size or type, when it is necessary to attract another vessel's attention. The rule sits in Part D, Sound and light signals, alongside the manoeuvring and warning signals of Rule 34 and the fog signals of Rule 35.

Which signals can't be used to attract attention?

Anything that can be mistaken for a signal authorised elsewhere in the rules. Part D alone has several that an improvised signal could imitate: the manoeuvring signals of Rule 34(a) and (b) — one, two or three short blasts, or flashes, meaning altering course to starboard, altering course to port, and operating astern propulsion; the doubt signal of Rule 34(d), at least five short and rapid blasts, which may be supplemented by at least five short and rapid flashes; and the one prolonged blast of Rule 34(e) at a bend. Rule 35 adds the fog signals — for example, one prolonged blast at intervals of not more than two minutes from a power-driven vessel making way through the water.

As we read it, that is the point of the limit: an attention signal that sounds like 'I am altering my course to port' tells the other vessel something false. If the situation is the one Rule 34(d) describes — vessels in sight of one another and approaching, and you either failing to understand the other's intentions or actions or in doubt whether she is taking sufficient action to avoid collision — then Rule 34(d) requires you to sound at least five short and rapid blasts 'immediately'. That is a Rule 34(d) signal, not a Rule 36 one.

Can a distress signal be used to attract attention?

No. Annex IV, section 2, prohibits using or exhibiting any of the distress signals except to indicate distress and need of assistance, and prohibits other signals that may be confused with them. A red hand-flare and a continuous sounding of the fog-signalling apparatus are both distress signals under Annex IV section 1 — not ways of getting a vessel to look at you.

Why must the light not look like an aid to navigation?

Because Rule 36 says so for any light used to attract another vessel's attention. In practice, a flashing light seen from a distance can be taken for a lit buoy or beacon, and an officer who reads it that way may misjudge both your position and the danger you are trying to show her.

Why are strobe lights to be avoided?

Rule 36 tells vessels to avoid high-intensity intermittent or revolving lights, with strobe lights as its example. It gives no reason. As we read it, the concerns are the same ones the rest of the rule guards against: a very bright flashing or revolving light can dazzle the people you are trying to warn, and is the kind of light most easily taken for an aid to navigation.

How should a searchlight be used under Rule 36?

The rule points the beam 'in the direction of the danger', and it must be used in such a way as not to embarrass any vessel.

As we read it, that means lighting up the hazard you want the other vessel to see, not her bridge, and 'embarrass' here means hamper: a beam shone into another vessel's wheelhouse costs her bridge team their night vision at exactly the moment you need them to see clearly.

Is a Rule 36 signal a distress signal?

No. Rule 36 is for attracting attention — to you, or to a danger the other vessel has not noticed. Rule 37 is for a vessel 'in distress and requires assistance', and requires the signals described in Annex IV. The two are kept apart from both sides: a Rule 36 signal must not be mistakable for a signal authorised elsewhere, and Annex IV prohibits using the distress signals for anything but distress.

How might Rule 36 come up in an MCA oral?

It may come up as a short question in its own right, or as a follow-up in a collision scenario. Examples of the kind of question to be ready for:

“How may you attract the attention of another vessel at night?”

“A small vessel ahead is standing into danger and does not seem to have seen it. What does Rule 36 let you do?”

“Can you sound five short blasts to attract attention?”

“Why shouldn't you use a strobe light?”

“Can you fire a red flare to get a ship's attention?”

Where do candidates go wrong on Rule 36?

The common slips: offering the doubt signal (at least five short and rapid blasts) or a red flare as an attention signal; forgetting the two limits on lights — not mistakable for an aid to navigation, and high-intensity intermittent or revolving lights to be avoided; shining the searchlight at the other vessel's bridge instead of in the direction of the danger; and mixing up Rule 36 with Rule 37.