Observe and identify
Advanced level, about 3 min. International COLREGs / IRPCS.
The situation
This action stage restarts the same authored watch. You are making eight knots in 60 m visibility and hear two sources apparently forward of your beam. Neither is in sight and collision risk has not been determined absent. Your boat can keep her course at two knots; eight knots leaves too little time to assess the unseen traffic. You can take precautionary action before finishing every identification.
What action should you take while the identities remain uncertain?
- Reduce to minimum course-keeping speed and reassess
- Keep eight knots until both vessel types are known
- Hold course and speed because the power-driven source must give way
Answers and explanations
Lookout: Uncertainty about a source is not a reason to wait at an unsafe speed. Keep engines ready, continue listening and reassess the developing situation.
When the situation changes
Despite slowing, further assessment now establishes that a close-quarters situation forward of the beam cannot be avoided at your remaining speed. The sources are still unseen. In these stated circumstances taking all way off is necessary.
Take all way off and continue with extreme caution
Rule 19(e) requires taking all way off when necessary. The checkpoint now supplies that necessity; minimum course-keeping speed is not a permanent safe-speed guarantee. The replay models deceleration to zero through the water. Real stopping may require stopping or reversing propulsion.
Keep two knots regardless of the new assessment
The new assessment establishes the need to take all way off. Minimum course-keeping speed does not remove that additional duty.
Accelerate before the unseen traffic gets closer
The close-quarters assessment requires removing way and extreme caution. Accelerating reduces the available assessment and stopping margin.
The sound answer
Reduce to minimum course-keeping speed and reassess
The forward fog signals and unresolved risk trigger Rule 19(e). Reduce to this vessel’s supplied two-knot minimum course-keeping speed and continue with extreme caution. You need not invent a unique identity for Source B before taking the required precaution.
Why the other options fall short
Keep eight knots until both vessel types are known
Waiting for unique identification can be impossible because Source B’s signal is shared. The unresolved risk and apparently forward signals already call for minimum course-keeping speed and extreme caution.
Hold course and speed because the power-driven source must give way
Neither vessel is in sight and the signals do not establish a crossing relationship. There is no supported stand-on entitlement from this sound evidence.
Rules 6 & 19(b), (e) · Act and reassess with limited evidence
Use a safe speed adapted to restricted visibility and keep a power-driven vessel’s engines ready for immediate manoeuvre. Unless collision risk has been determined absent, hearing a fog signal apparently forward of the beam requires minimum course-keeping speed. Take all way off if necessary and navigate with extreme caution until collision danger is over.