COLREG / ARPA / AIS Bridge Rule 8 🔒 Course / Premium

Action to Avoid Collision (Rule 8)

A target is inbound on a fine starboard bow, developing risk of collision.

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Scenario briefing

A target is inbound on a fine starboard bow, developing risk of collision. Apply Rule 8:

(a) AMPLE TIME act EARLY, while the other vessel still has plenty of room and time to read your intentions. In open water this is typically when TCPA is still 1020 minutes away (ranges of 48 NM for normal speeds); never in the last 23 minutes. "Ample" = enough time for the other ship to see, understand and react, and for you to verify your own action is working.

(b) SUBSTANTIAL readily apparent to the other vessel by eye AND on radar/AIS. A bold single alteration ( 20° of course, or 4 kt of speed) is vastly better than a series of small changes (Rule 8(b)).

(d) MONITOR keep checking CPA/TCPA after the action; be ready to alter further if the risk does not clear.

Make a single, bold, EARLY alteration and achieve CPA 1 NM.

Applicable COLREG rule(s)

Rule 8 — referenced in this scenario. Practising this scenario reinforces correct application under realistic time pressure.

📸 Bridge simulator scene

Captured directly from the SkipperCheck COLREG bridge simulator at scenario T = 0 — the moment the encounter begins.

SkipperCheck bridge simulator — COLREG Rule 8 — Action to avoid collision — radar PPI with AIS targets — Bridge-simulator scene under COLREG Rule 8 — Action to avoid collision. Captured from the SkipperCheck COLREG / ARPA / AIS bridge simulator.

Key teaching points

EARLY — act while TCPA is 10–20 minutes away, not in the last 2 minutes (Rule 8(a)).
SUBSTANTIAL — a single bold alteration (≥20° of course or ≥4 kt of speed) is far better than a series of small ones (Rule 8(b)).
READILY APPARENT — your action must be visible by eye AND on the other vessel's radar/AIS.
SAFE DISTANCE — the resulting CPA must be safe for the conditions (1 NM open water, less in confined waters).
MONITOR — keep checking CPA/TCPA after the action; be ready to act again (Rule 8(d)).

Common mistakes to avoid

A series of 5–10° heading nudges that the other vessel can't read on radar. Rule 8(b) explicitly forbids this.
Waiting "to see if she alters". Stand-on duty (Rule 17) does not delete your Rule 8 obligations as give-way.

Why it matters

Most collision-avoidance failures investigated by MAIB share one pattern: action was either too late, too small, or both. Rule 8 is the rule that tells you HOW to act once Rule 7 has confirmed risk of collision — and it is unforgiving about timidity.

Exam relevance

Rule 8 is examined in every COLREG-bearing exam from RYA Day Skipper to STCW OOW; the give-way candidate must talk through early, substantial, monitored action.

Related scenarios

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