Rule 37 — Distress Signals: Which Signals Count

What the rule requires

Two conditions have to hold together before the rule operates: the vessel is in distress and she requires assistance. When both hold, she shall use or exhibit the signals described in Annex IV, which the Inland text identifies for you as 33 CFR part 87 33 CFR §83.37. The International rule states the same requirement against its own annex, Annex IV to the Regulations COLREGs Rule 37. Neither text names a single signal, so any question that appears to be about Rule 37 is in practice an Annex IV question.

The sentence that decides more of those questions than any other is the opening line of the annex: the signals, used or exhibited either together or separately, indicate distress and need of assistance 33 CFR §87.01. One signal standing alone is a distress signal. A candidate who reasons that a combination is needed before the situation qualifies will pick the wrong option every time that idea is offered.

Sixteen entries follow, lettered (a) through (p). Instructors normally teach them grouped by channel rather than by letter, because nothing in the lettering is examinable and the grouping survives a closed-book exam. The grouping is lossy in one respect: it does not preserve the intervals, and the intervals are exactly what distractors alter. So take the timed signals first and separately.

Signals with an interval or a value attached

A gun or other explosive signal fired at intervals of about a minute.
A high intensity white light flashing at regular intervals from 50 to 70 times per minute.
Rockets or shells throwing red stars, fired one at a time at short intervals.
A continuous sounding with any fog-signalling apparatus.
A DSC distress alert on VHF channel 70, or on MF/HF at 2187.5, 8414.5, 4207.5, 6312, 12577 or 16804.5 kHz.

The gun is about a minute; the red star rockets are short intervals. Swapping those two is the single most common way an otherwise prepared candidate loses this question.

Flame and pyrotechnic

A rocket parachute flare or a hand flare showing a red light.
A smoke signal giving off orange-coloured smoke.
Flames on the vessel, as from a burning tar barrel or oil barrel.

Flag, shape and body

The International Code Signal of distress indicated by N.C.
A square flag having above or below it a ball, or anything resembling a ball.
Slowly and repeatedly raising and lowering arms outstretched to each side.

Both arms, out to each side, raised and lowered slowly and repeatedly. Waving one arm overhead, or waving a shirt on a boat hook, is not the signal the annex describes.

Radio and electronic

The spoken word Mayday by radiotelephony.
The group . . . - - - . . . (SOS) in Morse Code, made by any method.
A ship-to-shore alert from the vessel's Inmarsat or other mobile satellite service ship earth station.
Signals transmitted by emergency position-indicating radio beacons.
Signals transmitted by radiocommunication systems, including survival craft radar transponders meeting 47 CFR 80.1095.

A vessel two miles ahead is sounding her fog horn without pause on a clear afternoon. She shows nothing else. Is she in distress?

Yes. A continuous sounding with any fog-signalling apparatus is a distress signal under , and the annex states the signals indicate distress used together or separately. She does not have to add a flare, a flag or a radio call for the signal to count. Nothing in the rule conditions it on visibility either.

What has to be aboard

Rule 37 governs use of the signals. Carriage is a separate regulation with its own counts, and those counts are worth memorising because they are pure recall 46 CFR §28.145.

Ocean, more than 50 miles from the coastline — 3 parachute flares (approval series 160.136), 6 hand flares (160.121), 3 smoke signals (160.122).
Ocean 3 to 50 miles from the coastline, or more than 3 miles from the coastline on the Great Lakes — the same 3 parachute flares, 6 hand flares and 3 smoke signals, with the older approval series 160.036, 160.021, 160.022 and 160.037 also accepted.
Coastal waters excluding the Great Lakes, or within 3 miles of the coastline on the Great Lakes — night: one electric distress light (161.013) or 3 approved flares. Day: one distress flag (160.072), or 3 approved flares, or 3 approved smoke signals.
Both offshore rows carry the same numbers: three, six, three.

If flares are carried, the same 3 flares count toward both the day and the night requirement in coastal waters. The electric distress light satisfies night only, and the distress flag and smoke signals satisfy day only.

Telling it apart: Rule 36 against Rule 37

One criterion separates them: whether the signal appears on the Annex IV list. If it does, it means distress and nothing else. If it does not, it is at most a signal to attract attention, and the exam writes options that sit deliberately on the wrong side of that line.

A searchlight beam directed in the direction of the danger — Rule 36 COLREGs Rule 36. Permitted to attract another vessel's attention, and to be used so as not to embarrass any vessel. It is not on the Annex IV list and is not a distress signal.
Any other light or sound signal made to attract attention — allowed under Rule 36 only if it cannot be mistaken for any signal authorised elsewhere in the Rules, and any light used must not be mistakable for an aid to navigation.
High intensity intermittent or revolving lights, such as strobes — Rule 36 directs that their use be avoided for attracting attention. Separately, the white light flashing at 50 to 70 times per minute is on the distress list at 33 CFR §87.01.
Fog signals under Rule 35 — sounded at intervals of not more than 2 minutes: one prolonged blast making way, two prolonged blasts underway but stopped, one prolonged followed by two short for a vessel not under command, restricted in her ability to manoeuvre, constrained by her draft, sailing, fishing, or towing or pushing COLREGs Rule 35. None of these indicates distress. The distress version of the same apparatus is a continuous sounding, not a timed one.

Timed means fog. Continuous means distress. That distinction is doing the work in every question that puts you in restricted visibility and gives you a horn to interpret.

You are inbound at night and a vessel fine on the starboard bow directs the beam of her searchlight at a partly submerged container between you. What is she signalling?

She is attracting your attention to a danger under , which expressly permits directing the searchlight beam toward the danger. A searchlight beam is not among the Annex IV signals, so she is not indicating distress and need of assistance.

Working a question

At 0230 you are underway on inland waters. Off the port bow, an unlit small craft is showing a bright white light flashing rapidly, and a horn aboard her is sounding without a break. The question offers four readings: (A) she is attracting attention under Rule 36; (B) she is sounding a fog signal for a vessel underway but stopped; (C) she is in distress; (D) two signals are needed and she has shown only one, so the answer is doubtful.

Identify the waters. Inland, so the annex in play is the one Inland Rule 37 points to, 33 CFR part 87 33 CFR §83.37.
Test the horn first, because it is unambiguous. Continuous sounding with any fog-signalling apparatus is on the list 33 CFR §87.01. A Rule 35 fog signal is sounded at intervals of not more than 2 minutes and stops between blasts, which kills option B.
Rate the light before accepting it. The distress rate is 50 to 70 flashes per minute, which is between roughly five and six flashes in a five-second count, or 25 to 35 in thirty seconds. Count it against a watch rather than calling it by eye.
Dispose of option A. A light used to attract attention under Rule 36 must not be mistakable for a signal authorised elsewhere in the Rules, and a white light at this rate is authorised elsewhere as a distress signal.
Dispose of option D. The annex says the signals indicate distress used together or separately, so one would have sufficed and two do not create doubt.
Answer C.

Where candidates lose the point

Picking the searchlight as a distress signal. It attracts on the exam because it is the thing a mariner actually does when something is wrong, and because Rule 36 sits immediately before Rule 37 in the reading order. It is not on the Annex IV list.

Picking five short and rapid blasts. Candidates carry it over from manoeuvring signals and reach for it whenever a question involves a whistle and an emergency. No such signal appears in the Annex IV list at 33 CFR §87.01.

Colour swaps. Green star shells, white smoke, a green flare. The annex specifies red stars, a red light from the parachute or hand flare, and orange smoke. If the option changes the colour, the option is wrong however plausible the rest of it reads.

Shape and code swaps. A triangular flag with a ball, a square flag with a cone, the code signal "JV". The list gives a square flag with a ball above or below it, and the International Code Signal indicated by N.C.

Reading the gun as "short intervals". The gun or other explosive signal is fired at intervals of about a minute. Short intervals belongs to the red star rockets and shells, fired one at a time.

Treating a day carriage item as covering the night. Under 46 CFR §28.145 the concession runs one way only: flares count for day and night, but the distress flag and the smoke signals do not satisfy the night requirement.

Check yourself

(Inland) You sight a vessel firing an explosive signal at intervals of about one minute. What does this indicate?

Distress and need of assistance. A gun or other explosive signal fired at intervals of about a minute is listed at 33 CFR §87.01. The interval is the identifying feature; if the question gives short intervals instead, it is describing the red star rockets, which are also distress.

A vessel is displaying a square flag with a ball hanging beneath it. Is the ball in the wrong position?

No. The annex accepts a square flag having the ball above or below it, and accepts anything resembling a ball in place of one. Both arrangements are the distress signal.

Which of these may be used to attract attention without indicating distress: a burning oil barrel, orange smoke, the beam of a searchlight, or a red hand flare?

The searchlight beam, directed in the direction of the danger and used so as not to embarrass any vessel COLREGs Rule 36. Flames on the vessel from a burning oil barrel, an orange smoke signal and a red hand flare are all on the Annex IV distress list.

You are operating on the ocean 20 miles from the coastline. What visual distress signals must be aboard under 46 CFR §28.145?

Three parachute flares, six hand flares and three smoke signals, using approval series 160.136 or 160.036, 160.121 or 160.021, and 160.122, 160.022 or 160.037 46 CFR §28.145. The 3 to 50 mile row carries the same counts as the beyond-50-mile row; only the acceptable approval series differ.

A person in a liferaft is raising and lowering both arms, outstretched to each side, slowly and repeatedly. A second person is waving one arm overhead. Which is the recognised signal?

The first. The annex describes slowly and repeatedly raising and lowering arms outstretched to each side. A single waving arm is not the described signal, and exam options frequently offer it as the distractor.

You send a DSC distress alert on VHF. Which channel, and what MF/HF frequencies back it up?

VHF channel 70. On MF/HF the listed frequencies are 2187.5, 8414.5, 4207.5, 6312, 12577 and 16804.5 kHz .

In fog you hear one prolonged blast followed by two short blasts, repeated at intervals under two minutes. Distress?

No. That is the Rule 35 fog signal for a vessel not under command, restricted in her ability to manoeuvre, constrained by her draft, sailing, fishing, or towing or pushing COLREGs Rule 35. The distress use of a fog-signalling apparatus is a continuous sounding, with no interval between.