Final answer:
In case of a fire on a vessel, you should notify the captain, attempt to extinguish the fire, contain it by closing hatches and doors, and evacuate if needed, all while prioritizing safety and following the captain's instructions.
Step-by-step explanation:
If a fire starts on a vessel that can't be extinguished, the immediate actions you should take are: notify the captain and follow their instructions, attempt to extinguish the fire using available firefighting equipment (if safe to do so), close all hatches and doors to contain the fire, and evacuate the vessel if necessary. Remember to use the fire safety training you have received, which includes knowing the location of fire safety equipment and how to handle flammable materials properly. In any fire situation, the safety of all individuals on board is the highest priority, and actions should be taken swiftly but calmly to protect life and property.