Final answer:
When it is unsafe for vessel B to overtake vessel A, vessel A should sound five or more short and rapid blasts as a signal of disagreement with the proposed maneuver.
Step-by-step explanation:
If you are on vessel A and you hear vessel B sound a signal indicating its intention to overtake, but you feel it is not safe for vessel B to overtake at the present time, the correct action to take is to sound five or more short and rapid blasts of a whistle. This signal indicates doubt or disagreement with the proposed action, conveying that it is not safe to overtake at this time and alerting vessel B to your concerns. It's crucial in such situations to follow the appropriate navigational rules to ensure safety on the water.