Part B-ICritical
Rule 8: Action to avoid collision
Avoiding action must be early, clear, substantial and monitored until finally past and clear.
Detailed Explanation
This rule explains how to manoeuvre correctly:
A
Action must follow Part B and, when possible, be positive, timely, and seamanlike.
B
Alterations of course/speed should be large enough to be obvious visually and by radar; avoid multiple small changes.
C
With enough sea room, course alteration alone can be most effective if early/substantial and without creating a new close-quarters risk.
D
Action must produce safe passing distance, and effectiveness must be checked until finally past and clear.
E
If needed, slow, stop, or reverse propulsion to buy time and space.
F
For vessels required not to impede
- (i)act early to provide sea room
- (ii)obligation continues even when risk develops
- (iii)the vessel not to be impeded still has full Rule obligations when risk exists.
Key Points
- Action must be early, large and obvious
- Avoid a series of small alterations
- Monitor effect until finally past and clear
- Speed reduction alone can be effective action
Examples
- You are give-way in a crossing situation. You alter 40° to starboard — a large, readily apparent change per Rule 8(b) — and monitor ARPA to confirm CPA is improving.
- After altering course for a fishing fleet, you track the closest vessel on radar and verify your CPA has opened to 1.5 miles. Rule 8(d) requires checking until finally past and clear.
- A container ship makes a 5° course change that the other vessel cannot detect on radar. This violates Rule 8(b): the alteration must be large enough to be readily apparent.
Common Mistakes
- Making a series of small course changes that are not readily apparent to the other vessel.
- Failing to verify that the manoeuvre is actually achieving a safe CPA before considering the situation resolved.
- Reducing speed so slightly that the other vessel cannot detect the change on radar.