Describe the engine cooling system of the RB-M 45.

The RB-M 45 utilizes a closed-loop cooling system, which is designed to manage the temperature of the engine efficiently while preventing the introduction of contaminants from the surrounding environment. In a closed-loop system, coolant circulates through the engine, absorbing heat, and then flows through a heat exchanger or radiator where it dissipates that heat. This method allows for better temperature regulation and reduces the chances of corrosion and fouling, which can occur in open-loop systems where external water is drawn into the cooling circuit.

The design of the RB-M 45's cooling system emphasizes reliability and performance, as it ensures that the engines operate within optimal temperature ranges, thus enhancing overall efficiency and longevity. By using a closed-loop system, the cooling process remains independent of external water conditions, which is especially advantageous in varying marine environments.

This type of system contrasts with other options like open-loop systems, where water from the sea is used directly to cool the engine, potentially exposing it to marine organisms or debris. Similarly, convection-based and variable speed cooling systems do not accurately represent the specific design and functionality of the RB-M 45's cooling mechanism, making closed-loop the correct choice for this question.