Final answer:
When at anchor in restricted visibility and open water, it is recommended to ring the bell rapidly for about 5 seconds at intervals of no more than 2 minutes to notify other vessels (option b).
Step-by-step explanation:
When at anchor in restricted visibility and in open water, it is recommended to ring the bell rapidly for about 5 seconds at intervals of no more than 2 minutes (option b).
This is done to notify other vessels in the area about your presence and location, as well as to prevent any potential collisions.
By ringing the bell at regular intervals, other ships can hear the sound and take the necessary precautions to avoid your position.