Observe and identify
Foundation level, about 2 min. International COLREGs / IRPCS.
The situation
In restricted visibility, an unseen vessel sounds her operating signal. Listen to the entire signal and decide what it establishes.
What operating state does this signal indicate?
- A power-driven vessel making way through the water
- A power-driven vessel underway but stopped
- Specifically a sailing vessel
Answers and explanations
Lookout: Use the restricted-visibility context; a similar acoustic pattern can be used at a blind bend in clear weather.
The sound answer
A power-driven vessel making way through the water
Rule 35(a): one prolonged blast at intervals of not more than two minutes indicates a power-driven vessel making way through the water. The sound does not establish her heading.
Why the other options fall short
A power-driven vessel underway but stopped
A power-driven vessel stopped and making no way through the water sounds two prolonged blasts separated by about two seconds.
Specifically a sailing vessel
A sailing vessel uses the shared one-prolonged, two-short signal. A single prolonged blast here indicates a power-driven vessel making way.
Rule 35(a) · Power-driven making-way signal
A power-driven vessel making way through the water sounds one prolonged blast at intervals of not more than two minutes in or near restricted visibility.