Rule 8 — Action to Avoid Collision

TL;DR — Any action to avoid collision must be positive, made in ample time, and large enough to be readily apparent to another vessel observing visually or by radar; a succession of small alterations must be avoided. 33 CFR §83.08

---

What the Rule Says

Rule 8 is the operational backbone of collision avoidance. It does not tell you who must give way — that is the job of Rules 12 through 18 — but it tells you how any required action must be executed. Every give-way vessel, every stand-on vessel acting under Rule 17(a)(ii) or 17(b), and every vessel required not to impede another's passage must meet the standards set out here. 33 CFR §83.08

Paragraph (a) — The General Standard

Any action taken to avoid collision shall:

1. Be taken in accordance with Rules 4–19. 33 CFR §83.08 2. Be positive — half-hearted or tentative maneuvers do not satisfy the rule. 33 CFR §83.08 3. Be made in ample time — waiting until the last moment defeats the purpose. 33 CFR §83.08 4. Be made with due regard to the observance of good seamanship. 33 CFR §83.08

The phrase "if the circumstances of the case admit" appears throughout Rule 8. It acknowledges that confined waters, traffic density, or vessel characteristics may limit options, but it does not lower the standard — it simply recognizes that the standard must be applied to the actual situation. 33 CFR §83.08

Paragraph (b) — Magnitude of the Maneuver

Any alteration of course and/or speed shall, if the circumstances of the case admit, be large enough to be readily apparent to another vessel observing visually or by radar. 33 CFR §83.08

Critically: a succession of small alterations of course and/or speed should be avoided. 33 CFR §83.08

This is one of the most-tested sentences in Rule 8. A series of 5° course changes may eventually produce the same total alteration as one 30° change, but the other vessel — particularly one tracking you by radar — cannot detect the incremental changes in time to assess the developing situation. One bold, early maneuver is always preferred over a series of nibbles.

Paragraph (c) — Course Alteration Alone

If there is sufficient sea room, alteration of course alone may be the most effective action to avoid a close-quarters situation, provided that it is: 33 CFR §83.08

• Made in good time
• Substantial
• Does not result in another close-quarters situation

All three conditions must be satisfied simultaneously. A large course change made too late, or one that swings your vessel into a third vessel's path, does not comply. 33 CFR §83.08

Paragraph (d) — Passing at a Safe Distance

Action taken to avoid collision shall result in passing at a safe distance. The effectiveness of the action shall be carefully checked until the other vessel is finally past and clear. 33 CFR §83.08

This paragraph imposes a continuing duty of monitoring. Taking action and then returning your attention elsewhere is not sufficient. You must verify — visually or by radar — that the action is actually working and that the CPA (closest point of approach) is developing as intended. 33 CFR §83.08

Paragraph (e) — Speed Reduction

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

Note the disjunctive: speed reduction is authorized not only when collision is imminent but also when the mariner needs more time to evaluate the situation. This is a lawful and prudent option at any stage of a developing encounter. 33 CFR §83.08

Paragraph (f) — Vessels Required Not to Impede

This paragraph addresses the specific obligation of a vessel that is required by another rule not to impede the passage or safe passage of another vessel. Three sub-points apply: 33 CFR §83.08

(f)(i) Such a vessel shall, when required by the circumstances, take early action to allow sufficient sea room for the safe passage of the other vessel. 33 CFR §83.08

(f)(ii) The obligation not to impede is not relieved merely because the two vessels are now approaching so as to involve risk of collision. The vessel must still act, and when doing so must have full regard to the action that may be required by Rules 4–19. 33 CFR §83.08

(f)(iii) The vessel whose passage is not to be impeded remains fully obliged to comply with Rules 4–19 when the two vessels are approaching so as to involve risk of collision. 33 CFR §83.08

In plain terms: "not to impede" is a lower-tier obligation that applies before risk of collision develops. Once risk of collision exists, the full give-way/stand-on framework of Rules 12–18 applies to both vessels. 33 CFR §83.08

---

Why It Matters on the Exam

Rule 8 questions appear in multiple forms on the OUPV and Master 100 GT written examinations. Examiners test it both as a standalone rule and in combination with Rules 16 and 17.

Rule 8 and Rule 16 together define the complete obligation of the give-way vessel. Rule 16 requires early and substantial action to keep well clear 33 CFR §83.16; Rule 8 specifies that the action must be large enough to be readily apparent and must not consist of a succession of small changes. 33 CFR §83.08 Exam questions often present a scenario where a give-way vessel makes several small course changes and ask whether this complies — the answer is no.

Rule 8 and Rule 17 together define the stand-on vessel's options. Rule 17(a)(i) requires the stand-on vessel to maintain course and speed. 33 CFR §83.17 Rule 17(a)(ii) permits the stand-on vessel to maneuver alone once it becomes apparent the give-way vessel is not acting. 33 CFR §83.17 Rule 17(b) requires the stand-on vessel to act when collision cannot be avoided by the give-way vessel alone. 33 CFR §83.17 In all of these cases, whatever action the stand-on vessel takes must still meet the Rule 8 standard: positive, timely, and large enough to be apparent. 33 CFR §83.08

Rule 8(e) — speed reduction is frequently tested. Candidates sometimes believe that only course changes are authorized. The rule explicitly includes slackening speed, stopping, or reversing. 33 CFR §83.08

Rule 8(f) — not to impede is tested in the context of narrow channels (Rule 9) and traffic separation schemes (Rule 10). The key exam point is that once risk of collision exists, the "not to impede" obligation does not replace the collision avoidance rules — both vessels must comply with Rules 4–19. 33 CFR §83.08

Responsibilities between vessel types (Rule 18) establish who is the give-way vessel in mixed-traffic encounters. 33 CFR §83.18 Once that hierarchy is established, Rule 8 governs how the give-way vessel must act. For example, a power-driven vessel required to keep clear of a sailing vessel 33 CFR §83.18 must execute that maneuver in a manner that is positive, timely, and readily apparent. 33 CFR §83.08

---

Common Pitfalls

Pitfall 1 — Confusing "who" with "how." Rule 8 does not assign give-way or stand-on status. That comes from Rules 12–18. Rule 8 only governs the manner of execution. Candidates who conflate the two will misread scenario questions. 33 CFR §83.08

Pitfall 2 — Believing small, incremental changes are acceptable if they total a large alteration. The rule explicitly prohibits a succession of small alterations. The other vessel must be able to detect the maneuver visually or by radar. 33 CFR §83.08

Pitfall 3 — Forgetting the continuing duty to monitor. Taking action and then assuming the situation is resolved is not compliant. The effectiveness of the action must be checked until the other vessel is finally past and clear. 33 CFR §83.08

Pitfall 4 — Treating speed reduction as a last resort. Paragraph (e) authorizes speed reduction to allow more time to assess the situation — not only when collision is imminent. 33 CFR §83.08

Pitfall 5 — Believing the "not to impede" obligation disappears once risk of collision exists. It does not disappear; it is supplemented by the full collision avoidance rules. Both vessels must comply with Rules 4–19 once risk of collision is present. 33 CFR §83.08

Pitfall 6 — Assuming the stand-on vessel is always passive. Rule 17(a)(ii) permits the stand-on vessel to maneuver once it is apparent the give-way vessel is not acting, and Rule 17(b) requires action when collision cannot otherwise be avoided. 33 CFR §83.17 Any such action must still satisfy Rule 8. 33 CFR §83.08

---

Quick Check

Q1 — A give-way vessel makes four successive 5° course alterations over ten minutes. Does this comply with Rule 8?

No. Rule 8(b) states that a succession of small alterations of course and/or speed should be avoided. Any alteration shall, if the circumstances of the case admit, be large enough to be readily apparent to another vessel observing visually or by radar. Four incremental 5° changes are unlikely to be detectable by the other vessel in time to be useful. 33 CFR §83.08

Q2 — At what point is a vessel authorized to reduce speed under Rule 8?

A vessel may slacken speed, stop, or reverse her means of propulsion if necessary to avoid collision or to allow more time to assess the situation. Speed reduction is not limited to imminent-collision scenarios. 33 CFR §83.08

Q3 — A vessel is required not to impede a vessel in a narrow channel. Risk of collision now exists between them. Is the "not to impede" vessel relieved of its obligation?

No. Rule 8(f)(ii) states that a vessel required not to impede the passage of another vessel is not relieved of that obligation merely because risk of collision has developed. It must take action and must have full regard to the action required by Rules 4–19. Additionally, Rule 8(f)(iii) confirms that the vessel whose passage is not to be impeded remains fully obliged to comply with Rules 4–19. 33 CFR §83.08

Q4 — When may a course alteration alone be the most effective action under Rule 8?

When there is sufficient sea room, a course alteration alone may be the most effective action, provided it is made in good time, is substantial, and does not result in another close-quarters situation. All three conditions must be met. 33 CFR §83.08

Q5 — After taking action to avoid collision, when may a mariner consider the obligation under Rule 8(d) satisfied?

Not until the other vessel is finally past and clear. The effectiveness of the action must be carefully checked throughout the entire passing. 33 CFR §83.08

Q6 — A power-driven vessel is the stand-on vessel in a crossing situation. The give-way vessel is not acting. The stand-on vessel decides to maneuver. What restriction applies to her course alteration under Rule 17?

A power-driven vessel taking action under Rule 17(a)(ii) in a crossing situation to avoid collision with another power-driven vessel shall, if the circumstances of the case admit, not alter course to port for a vessel on her own port side. 33 CFR §83.17 Any maneuver taken must also satisfy the Rule 8 standard of being positive, timely, and readily apparent. 33 CFR §83.08