Which two types of exhaust systems must all vessels have?

The correct answer highlights that all vessels must have exhaust systems that include both mechanically powered and natural means of exhaust.

Mechanically powered exhaust systems are essential for vessels that have engines that produce exhaust gases. These systems help to efficiently remove these gases from the engine compartment, ensuring the safety and performance of the vessel. By utilizing a mechanical method—often a fan or blower—this type of exhaust system can facilitate the removal of harmful fumes that could otherwise accumulate and pose a risk to those onboard.

Natural means of exhaust systems, on the other hand, refer to designs that utilize the natural flow of air and gases, often relying on gravitational forces or the natural movement of air. This is common in systems that allow exhaust to rise and escape freely from areas where a vessel's engine operates.

The combination of these two types of systems ensures that a vessel is equipped to handle exhaust efficiently, addressing safety concerns, maintaining engine efficiency, and complying with regulatory requirements. Each system plays a crucial role in the overall functionality and safety of the vessel, making their presence both necessary and complementary.