Rule 37 — Distress Signals

TL;DR — When a vessel is in distress and requires assistance, she must use signals listed in Annex IV (33 CFR Part 87). Those signals are reserved exclusively for distress; using them for any other purpose is prohibited. 33 CFR §83.37 33 CFR §87.02

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What the Rule Says

Rule 37 itself is deliberately brief. The entire text of the Inland Rule reads: "When a vessel is in distress and requires assistance she shall use or exhibit the signals described in Annex IV to these Rules (33 CFR part 87)." 33 CFR §83.37

The substance of the rule lives in Annex IV, codified at 33 CFR Part 87. Section 87.01 enumerates sixteen recognized distress signals, any of which may be used alone or in combination. 33 CFR §87.01

The Complete List of Recognized Distress Signals

The following signals, used or exhibited either together or separately, indicate distress and need of assistance 33 CFR §87.01:

(a) Gun or explosive signal — A gun or other explosive signal fired at intervals of about one minute. 33 CFR §87.01

(b) Continuous fog signal — A continuous sounding with any fog-signaling apparatus. 33 CFR §87.01

(c) Red star rockets — Rockets or shells throwing red stars, fired one at a time at short intervals. 33 CFR §87.01

(d) SOS by Morse Code — A signal made by any method consisting of the group · · · — — — · · · (SOS) in Morse Code. 33 CFR §87.01

(e) Mayday by radiotelephony — A signal sent by radiotelephony consisting of the spoken word "Mayday." 33 CFR §87.01

(f) International Code Signal N.C. — The International Code Signal of distress indicated by N.C. 33 CFR §87.01

(g) Square flag with ball — A signal consisting of a square flag having above or below it a ball or anything resembling a ball. 33 CFR §87.01

(h) Flames on the vessel — Flames on the vessel, as from a burning tar barrel, oil barrel, or similar. 33 CFR §87.01

(i) Red flare — A rocket parachute flare or a hand flare showing a red light. 33 CFR §87.01

(j) Orange smoke — A smoke signal giving off orange-colored smoke. 33 CFR §87.01

(k) Arms raised and lowered — Slowly and repeatedly raising and lowering arms outstretched to each side. 33 CFR §87.01

(l) DSC distress alert — A distress alert by means of digital selective calling (DSC) transmitted on VHF Channel 70, or on MF/HF frequencies 2187.5 kHz, 8414.5 kHz, 4207.5 kHz, 6312 kHz, 12577 kHz, or 16804.5 kHz. 33 CFR §87.01

(m) Satellite distress alert — A ship-to-shore distress alert transmitted by the ship's Inmarsat or other mobile satellite service provider ship earth station. 33 CFR §87.01

(n) EPIRB — Signals transmitted by emergency position-indicating radio beacons. 33 CFR §87.01

(o) Survival craft radar transponders — Signals transmitted by radiocommunication systems, including survival craft radar transponders meeting the requirements of 47 CFR 80.1095. 33 CFR §87.01

(p) High-intensity white light — A high-intensity white light flashing at regular intervals from 50 to 70 times per minute. 33 CFR §87.01

Exclusive Use Prohibition

Section 87.02 closes the loop: use or exhibition of any of the foregoing signals except for the purpose of indicating distress and need of assistance is prohibited. Likewise, use of other signals that may be confused with any of the above signals is prohibited. 33 CFR §87.02

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Why It Matters on the Exam

OUPV and Master 100 GT written exams test Rule 37 / Annex IV in several recurring ways. Understanding the structure of the rule — a short operative provision pointing to a detailed annex — helps you answer both identification questions and application questions correctly.

Signal Identification Questions

The most common exam format presents a description of a signal and asks whether it is a recognized distress signal, or presents a list and asks which item does NOT belong. You must know all sixteen signals in 33 CFR §87.01 with enough precision to distinguish them from signals that are merely authorized elsewhere in the Rules.

Key distinctions the exam exploits:

Color matters for pyrotechnics. Red stars, red hand flares, and red parachute flares are distress signals. 33 CFR §87.01 Orange smoke is a distress signal. 33 CFR §87.01 A white flare is not listed as a distress signal in Annex IV — it appears in the Rules only as a signal to attract attention under Rule 36, which is a separate provision. 33 CFR §83.36

The high-intensity white light has a specific flash rate. The rate is 50 to 70 flashes per minute. 33 CFR §87.01 Exam distractors will offer incorrect rates; memorize the range.

The fog signal distress use is continuous. A continuous sounding with any fog-signaling apparatus is a distress signal. 33 CFR §87.01 Contrast this with the interval-based fog signals prescribed under Rule 35, which are not distress signals. 33 CFR §83.35 The word "continuous" is the operative distinction.

The gun signal interval is about one minute. A gun or explosive signal fired at intervals of about a minute is a distress signal. 33 CFR §87.01 Do not confuse this with the two-minute intervals used for fog signals under Rule 35. 33 CFR §83.35

The arm signal requires a specific motion. Slowly and repeatedly raising and lowering arms outstretched to each side. 33 CFR §87.01 Waving arms rapidly or in another pattern is not the prescribed signal.

Exclusive Use Questions

Exam questions frequently test whether a mariner may use a distress signal for a non-distress purpose. The answer is always no. Section 87.02 prohibits use of any Annex IV signal except to indicate distress and need of assistance. 33 CFR §87.02 This prohibition also extends to signals that may be confused with Annex IV signals. 33 CFR §87.02

A common scenario: a vessel operator fires a red flare to signal a marina that the vessel is returning to dock. This is a violation. The red flare is a recognized distress signal under 33 CFR §87.01(i) 33 CFR §87.01, and its use for any purpose other than indicating distress is prohibited under 33 CFR §87.02. 33 CFR §87.02

"Together or Separately" Language

The rule states that the listed signals may be used "either together or separately." 33 CFR §87.01 No single signal is mandatory; any one of the sixteen is sufficient to constitute a recognized distress signal. Exam questions sometimes imply that a vessel must use a specific signal — that is incorrect. The mariner selects whichever signal or combination of signals is available and appropriate to the situation.

Relationship to Rule 36

Rule 36 authorizes any vessel to make light or sound signals to attract attention, provided those signals cannot be mistaken for any signal authorized elsewhere in the Rules. 33 CFR §83.36 Rule 36 signals are not distress signals. The exam may present a scenario and ask whether the appropriate action is a Rule 36 attention signal or a Rule 37 distress signal. The controlling factor is whether the vessel is in distress and requires assistance. If yes, Rule 37 and Annex IV apply. 33 CFR §83.37

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Common Pitfalls

Pitfall 1: Confusing orange smoke with any other smoke color. The distress signal is orange-colored smoke. 33 CFR §87.01 No other smoke color is listed. Exam distractors may offer "black smoke" or "white smoke" — neither is a recognized distress signal under Annex IV.

Pitfall 2: Misidentifying the N.C. flag signal. The International Code Signal of distress is N.C. 33 CFR §87.01 This is a two-flag hoist from the International Code of Signals. Do not confuse it with the square flag and ball signal, which is a separate and distinct entry. 33 CFR §87.01

Pitfall 3: Treating the continuous fog signal as a Rule 35 signal. Under Rule 35, fog signals are sounded at prescribed intervals — not continuously. 33 CFR §83.35 A continuous sounding of a fog-signaling apparatus is an Annex IV distress signal, not a Rule 35 fog signal. 33 CFR §87.01 The continuity is what makes it a distress signal.

Pitfall 4: Assuming the white flashing light is always a distress signal. The high-intensity white light is a distress signal only when it flashes at 50 to 70 times per minute. 33 CFR §87.01 A white light flashing at a different rate is not an Annex IV distress signal.

Pitfall 5: Forgetting that DSC distress alerts have specific frequencies. VHF Channel 70 is the DSC distress channel. The MF/HF DSC frequencies are 2187.5 kHz, 8414.5 kHz, 4207.5 kHz, 6312 kHz, 12577 kHz, and 16804.5 kHz. 33 CFR §87.01 Exam questions may list an incorrect frequency as a distractor.

Pitfall 6: Believing a vessel must be underway to use distress signals. Rule 37 applies whenever a vessel is in distress and requires assistance — there is no restriction based on the vessel's status or condition. 33 CFR §83.37

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Quick Check

Q1: A vessel operator fires a red parachute flare to signal a passing vessel that he wants to communicate. Has he violated any rule?

Yes. A rocket parachute flare showing a red light is a recognized distress signal under 33 CFR §87.01(i). 33 CFR §87.01 Use of any Annex IV signal for any purpose other than indicating distress and need of assistance is prohibited under 33 CFR §87.02. 33 CFR §87.02

Q2: Which of the following is a recognized distress signal: (A) white smoke, (B) orange smoke, (C) black smoke, (D) green smoke?

(B) Orange smoke. A smoke signal giving off orange-colored smoke is listed in 33 CFR §87.01(j). 33 CFR §87.01 No other smoke color appears in Annex IV.

Q3: At what flash rate must a high-intensity white light flash to qualify as a distress signal?

From 50 to 70 times per minute, at regular intervals. 33 CFR §87.01

Q4: A vessel is sounding her fog horn continuously. Is this a Rule 35 fog signal or a distress signal?

It is a distress signal. A continuous sounding with any fog-signaling apparatus is listed in 33 CFR §87.01(b) as a distress signal. 33 CFR §87.01 Rule 35 fog signals are sounded at prescribed intervals, not continuously. 33 CFR §83.35

Q5: Must a vessel in distress use all sixteen Annex IV signals simultaneously?

No. The signals listed in 33 CFR §87.01 may be used either together or separately. 33 CFR §87.01 Any single recognized signal, or any combination, is sufficient.

Q6: On which VHF channel is a DSC distress alert transmitted?

VHF Channel 70. 33 CFR §87.01

Q7: What is the difference between a Rule 36 attention signal and a Rule 37 distress signal?

A Rule 36 signal is used to attract the attention of another vessel and must not be mistakable for any signal authorized elsewhere in the Rules. 33 CFR §83.36 A Rule 37 distress signal is used when a vessel is in distress and requires assistance, and must be one of the signals enumerated in Annex IV (33 CFR Part 87). 33 CFR §83.37 33 CFR §87.01 The controlling factor is whether the vessel is in distress and requires assistance.

Q8: A square flag is hoisted with a round ball below it. Is this a recognized distress signal?

Yes. A signal consisting of a square flag having above or below it a ball or anything resembling a ball is a recognized distress signal under 33 CFR §87.01(g). 33 CFR §87.01 The ball may be above or below the flag.