Rule 6 — Safe Speed

TL;DR — Every vessel must at all times proceed at a safe speed so she can take proper and effective action to avoid collision and be stopped within a distance appropriate to prevailing circumstances. Six factors apply to all vessels; six additional factors apply specifically to vessels with operational radar. 33 CFR §83.06

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What the Rule Says

The Core Obligation

The rule imposes a continuous, unconditional duty: "every vessel shall at all times proceed at a safe speed." 33 CFR §83.06 There is no exception for good weather, open water, or daylight. The standard has two components that must both be satisfied simultaneously:

1. The vessel must be able to take proper and effective action to avoid collision. 2. The vessel must be able to be stopped within a distance appropriate to the prevailing circumstances and conditions. 33 CFR §83.06

Neither component alone is sufficient. A vessel that can maneuver but cannot stop in time, or can stop but cannot maneuver effectively, is not proceeding at a safe speed.

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Factors Considered by All Vessels (Six Factors)

The rule enumerates the following factors that every vessel — regardless of equipment — must take into account when determining a safe speed 33 CFR §83.06:

(i) State of visibility. Restricted visibility is defined as any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms, or any other similar causes. 33 CFR §83.03 Reduced visibility directly compresses the time available to detect a hazard and take avoiding action, requiring a corresponding reduction in speed.

(ii) Traffic density, including concentration of fishing vessels or any other vessels. High traffic density — whether commercial shipping lanes, a fishing fleet, or a crowded anchorage — increases the probability of a close-quarters situation developing. 33 CFR §83.06

(iii) Maneuverability of the vessel, with special reference to stopping distance and turning ability in the prevailing conditions. A deeply laden barge tow has a vastly different stopping distance than a light outboard vessel. The mariner must account for the actual maneuvering characteristics of the vessel being operated, not a theoretical average. 33 CFR §83.06

(iv) At night, the presence of background light such as from shore lights or from back scatter of her own lights. Background lighting can mask the lights of other vessels or create false impressions of bearing and distance. This factor applies exclusively at night. 33 CFR §83.06

(v) State of wind, sea, and current, and the proximity of navigational hazards. Adverse sea state, strong current, and nearby shoals, rocks, or other hazards all reduce the margin available for safe maneuvering. 33 CFR §83.06

(vi) Draft in relation to the available depth of water. A vessel operating with minimal underkeel clearance may be unable to maneuver freely or stop effectively. This factor is particularly relevant in shallow coastal and inland waters. 33 CFR §83.06

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Additional Factors for Vessels with Operational Radar (Six More Factors)

Vessels equipped with operational radar must additionally consider 33 CFR §83.06:

(i) The characteristics, efficiency, and limitations of the radar equipment. No radar set is perfect. Beam width, antenna rotation rate, minimum range, and display resolution all affect what can and cannot be reliably detected. 33 CFR §83.06

(ii) Any constraints imposed by the radar range scale in use. A vessel using a long-range scale gains early warning of distant contacts but loses resolution at close range. A vessel using a short-range scale has good close-in resolution but may not detect a fast-closing contact in time. The range scale selected must be appropriate to the situation. 33 CFR §83.06

(iii) The effect on radar detection of sea state, weather, and other sources of interference. Sea clutter, rain clutter, and interference from other radar sets can mask genuine targets. The mariner must not assume that a clear radar screen means clear water. 33 CFR §83.06

(iv) The possibility that small vessels, ice, and other floating objects may not be detected by radar at an adequate range. Small wooden or fiberglass vessels, growlers, and debris present minimal radar cross-sections and may not appear on the display until dangerously close. 33 CFR §83.06

(v) The number, location, and movement of vessels detected by radar. Multiple contacts require systematic tracking. A vessel that is monitoring several targets simultaneously must ensure its speed allows time to assess each developing situation. 33 CFR §83.06

(vi) The more exact assessment of the visibility that may be possible when radar is used to determine the range of vessels or other objects in the vicinity. Radar can help quantify actual visibility conditions by comparing the range at which known objects first appear on the display against their charted positions. This information feeds back into the overall safe-speed determination. 33 CFR §83.06

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Relationship to Other Rules

Safe speed is not an isolated concept. It connects directly to the obligation to take collision-avoidance action that is positive, made in ample time, and large enough to be readily apparent to another vessel. 33 CFR §83.08 If a vessel is proceeding too fast, it may be unable to execute the kind of bold, timely maneuver that Rule 8 demands. Additionally, if necessary to avoid collision or to allow more time to assess the situation, a vessel shall slacken her speed or take all way off by stopping or reversing her means of propulsion. 33 CFR §83.08 That obligation presupposes that the vessel had a speed to slacken in the first place — and that the speed was one from which stopping was actually achievable.

The hierarchy of vessels established by Rule 18 is also relevant context. A power-driven vessel underway must keep out of the way of a vessel not under command, a vessel restricted in her ability to maneuver, a vessel engaged in fishing, and a sailing vessel. 33 CFR §83.18 Proceeding at a speed that does not allow adequate time to detect and yield to a privileged vessel is a failure of the safe-speed obligation.

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Why It Matters on the Exam

Exam questions on Rule 6 test several recurring themes:

"At all times" is absolute. The rule contains no carve-outs. Candidates sometimes assume that good visibility or light traffic eliminates the safe-speed obligation. It does not. 33 CFR §83.06

The rule applies to every vessel. The opening language is "every vessel." This includes sailing vessels, vessels engaged in fishing, and vessels restricted in their ability to maneuver — not just power-driven vessels. 33 CFR §83.06

Radar does not permit higher speed. A common distractor answer suggests that having operational radar allows a vessel to maintain speed in restricted visibility. The rule does not say this. Radar adds six additional factors to consider; it does not suspend the safe-speed obligation or authorize a higher speed. 33 CFR §83.06

Know the count: 6 + 6. Exam questions frequently ask how many factors apply to all vessels (six) versus how many additional factors apply to radar-equipped vessels (six). The total is twelve enumerated factors, but the rule states these are "among those taken into account" — the list is not exhaustive. 33 CFR §83.06

Draft and underkeel clearance is a factor. Candidates sometimes overlook factor (vi) — draft in relation to available depth of water. This is explicitly listed and has appeared on exams. 33 CFR §83.06

Background light at night is a factor. Factor (iv) is night-specific and addresses both shore lights and back scatter from the vessel's own lights. This is a detail that distinguishes candidates who have read the rule carefully. 33 CFR §83.06

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Common Pitfalls

Pitfall 1: Confusing "restricted visibility" with "darkness." Restricted visibility is a defined term: fog, mist, falling snow, heavy rainstorms, sandstorms, or any other similar causes. 33 CFR §83.03 Darkness alone is not restricted visibility. Night operations are addressed separately under factor (iv) of Rule 6. 33 CFR §83.06

Pitfall 2: Assuming radar eliminates the need to reduce speed. Operational radar adds factors to the safe-speed analysis; it does not replace the underlying obligation. Small vessels, ice, and floating objects may not be detected at adequate range even with radar. 33 CFR §83.06

Pitfall 3: Treating the factor list as exhaustive. The rule says these factors "shall be among those taken into account." The list is illustrative, not limiting. An exam question may describe a scenario with an unlisted factor and ask whether safe speed is still relevant — the answer is yes. 33 CFR §83.06

Pitfall 4: Forgetting that stopping distance is vessel-specific. Factor (iii) requires consideration of the maneuverability of the specific vessel, with special reference to stopping distance and turning ability in the prevailing conditions. 33 CFR §83.06 A candidate who applies a generic standard rather than the characteristics of the vessel in the question will select the wrong answer.

Pitfall 5: Overlooking the connection to Rule 8. Safe speed and collision-avoidance action are interdependent. A vessel that cannot execute a bold, timely maneuver because of excessive speed has violated both Rule 6 and the spirit of Rule 8. 33 CFR §83.08

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Quick Check

Q1: What are the two performance standards a vessel must meet to be proceeding at a safe speed?

She must be able to (1) take proper and effective action to avoid collision, and (2) be stopped within a distance appropriate to the prevailing circumstances and conditions. 33 CFR §83.06

Q2: How many factors does Rule 6 list for all vessels, and how many additional factors apply to vessels with operational radar?

Six factors apply to all vessels; six additional factors apply to vessels with operational radar, for a total of twelve enumerated factors. 33 CFR §83.06

Q3: Does having operational radar permit a vessel to maintain higher speed in restricted visibility?

No. Radar adds six additional factors to the safe-speed analysis but does not suspend the obligation or authorize a higher speed. 33 CFR §83.06

Q4: Which Rule 6 factor is explicitly limited to nighttime operations?

Factor (iv): the presence of background light such as from shore lights or from back scatter of her own lights. 33 CFR §83.06

Q5: Is darkness alone considered "restricted visibility" under the Rules?

No. Restricted visibility is defined as conditions in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms, or any other similar causes. Darkness is not included in that definition. 33 CFR §83.03

Q6: A sailing vessel is transiting a fog bank. Does Rule 6 apply to her?

Yes. Rule 6 applies to "every vessel" at all times. Sailing vessels are not exempt. 33 CFR §83.06

Q7: Which Rule 6 factor addresses the vessel's own physical characteristics rather than external conditions?

Factor (iii): the maneuverability of the vessel with special reference to stopping distance and turning ability in the prevailing conditions. 33 CFR §83.06

Q8: Why might a vessel operating in shallow water need to reduce speed even in good visibility and light traffic?

Factor (vi) requires consideration of draft in relation to available depth of water. Minimal underkeel clearance may restrict the vessel's ability to maneuver or stop effectively. 33 CFR §83.06