Observe and identify
Advanced level, about 3 min. International COLREGs / IRPCS.
The situation
Two sound sources are apparently forward of your beam in restricted visibility. Neither vessel is in sight. Listen to each complete sequence, using the source timelines if needed. This recognition stage reconstructs the available evidence; continue to the action stage to make a watchkeeping decision.
What can you establish from the two signals?
- A is power-driven and making way; B could belong to several operating groups
- A is power-driven and making way; B is definitely a trawler
- A is crossing from starboard and must stand on; B must give way
Answers and explanations
Lookout: Keep the two sources separate. A shared operating signal does not identify a unique vessel type, and neither sequence establishes a heading.
The sound answer
A is power-driven and making way; B could belong to several operating groups
Source A sounds one prolonged blast, the Rule 35(a) power-driven making-way signal. Source B sounds one prolonged followed by two short blasts: sailing, fishing, NUC, RAM, draught-constrained and towing or pushing share it. These signals do not establish either heading or a stand-on entitlement.
Why the other options fall short
A is power-driven and making way; B is definitely a trawler
The first assessment is supported, but the second is too specific. The one-prolonged, two-short operating signal is shared by several groups and cannot identify a trawler by sound alone.
A is crossing from starboard and must stand on; B must give way
The sound does not establish either heading, and these vessels are not in sight. In-sight crossing duties cannot be assigned from these observations; restricted-visibility conduct governs the encounter.
Rule 35(a), (c) · Distinct signals, limited identities
A power-driven vessel making way sounds one prolonged blast. The one-prolonged, two-short sequence is shared by vessels sailing, fishing, not under command, restricted in manoeuvrability, constrained by draught, or towing or pushing. Each is repeated at intervals of not more than two minutes in or near restricted visibility.