If you are in an 18-meter tug crossing a narrow channel and sight a tankship coming up the channel, what is your obligation?

• A. You cannot impede the safe passage of the tankship
• B. You must slow to a stop and drift
• C. You should pass ahead on the tankship's port side
• D. You should hail the tankship and request passage

Answer: (A)

In a narrow-channel situation, vessels that are constrained to maneuver within the channel have priority, and other vessels must not impede their safe passage. The tankship coming up the channel is within the channel and therefore limited by its confines, so you as the tug must take action that ensures the tankship can pass safely without obstruction. Practically, that means adjusting your actions early—potentially stopping or waiting—so you do not block the tankship’s path. Merely drifting or continuing to cross could block its passage, and passing ahead on the tankship’s side or simply hailing does not fulfill the obligation to keep the channel clear. The key idea is never to impede the safe passage of a vessel constrained to the channel.