What is the key reason for having a fire extinguisher on board a boat?

The key reason for having a fire extinguisher on board a boat is to extinguish potential fire hazards. Boats are particularly susceptible to fires due to the presence of flammable materials like fuel, oil, and other goods. A fire can start quickly and spread rapidly in an enclosed space on water, making it crucial to have the means to combat it. Having a fire extinguisher ensures that, in case of an emergency, the crew can respond immediately to control or eliminate a fire before it escalates into a more dangerous situation.

The other options do not serve the primary safety function of a fire extinguisher. Impressing passengers is not a legitimate reason for safety equipment, while a fire extinguisher is not effective as a flotation device and does not function as a signaling tool for help.