The correct answer is B) Clear the afterdeck and fantail of personnel. When maneuvering on a towing hook, it is crucial to ensure the safety of personnel on the vessel. Clearing the afterdeck and fantail of personnel is necessary to prevent potential injuries from the movement and tension of the towing hook. This is a standard safety precaution required by maritime regulations to protect crew members from the hazards associated with towing operations. The other options are incorrect because: A) Lashing the hook closed is not necessary and may interfere with the towing operation; C) The towing winch engine does not need to be running for maneuvering on the towing hook; and D) Slow bell operation is not a specific requirement for this safety precaution.