On a cargo vessel, when must fire and boat drills be conducted after crew replacement?

The requirement for conducting fire and boat drills on a cargo vessel after crew replacement is based on safety procedures established to ensure that all crew members are familiar with emergency protocols as soon as they join the vessel. Conducting drills 24 hours after 25% replacement ensures that a significant proportion of the crew is trained and competent in emergency procedures in a timely manner, allowing the new members to learn and practice necessary skills without delay.

This timeframe is crucial because it helps integrate new crew members into the vessel's safety culture promptly, enhancing overall preparedness for emergencies. By emphasizing the importance of conducting drills shortly after crew changes, the vessel maintains a high level of readiness and safety, especially since operational conditions can change quickly at sea.

The other choices suggest longer periods before conducting drills, which would compromise crew readiness and safety. It's essential that new crew members interact and drill with their colleagues to understand their roles in an emergency, which is why the specified 24-hour period following a 25% crew replacement is the most effective practice.