You are unsure whether risk of collision exists. How do you treat it?
Treat it as existing and act. The sign: the compass bearing of the approaching vessel does not appreciably change.
Rule 7 (a), (d).
Part of the convention Always: clear weather and fog alike
The master rule of doubt: if in doubt, assume the risk exists. Determine it by all available means, not by eye alone.
- If the compass bearing of an approaching vessel does not appreciably change, risk of collision exists.
- Risk may exist even with an appreciably changing bearing: with a very large vessel, with a tow, or when closing at short range.
- Use radar properly if fitted and working: long-range scanning for early warning, and radar plotting or equivalent systematic observation of the contacts.
- Do not make assumptions on the basis of scanty information, especially scanty radar information.
At sea it looks like this
A light stays exactly 40 degrees on your starboard bow and has not moved for five minutes, only grown. The bearing is constant, so you are heading for the same point of water. Act now.
The rule says“If there is any doubt such risk shall be deemed to exist.”
Check yourself
How do you tell that a risk of collision exists?
The bearing of the other vessel does not change while the range decreases. With a very large vessel, with a tow and at close range risk can exist on a changing bearing too, and scanty information counts as risk by itself.
Rule 7 (d).