What is the duty of the sea-water pump in a marine diesel system?

The sea-water pump plays a crucial role in a marine diesel system by circulating seawater through the cooling system. This process is essential for maintaining the engine's operating temperature by effectively removing excess heat. The seawater absorbs heat from the engine components, helping to prevent overheating and ensuring efficient engine performance. This circulation allows for efficient heat transfer away from the engine and into the surrounding water, which is vital for the longevity and reliability of the engine.

Other options focus on different functions not associated with the seaward pump's responsibilities. For example, circulating air through the cooling system is not part of the pump's function, as air cannot efficiently transfer heat like seawater can. Supplying fuel to the engine pertains to the fuel system rather than the cooling system, and increasing the engine's horsepower relates to performance enhancements rather than directly to cooling mechanisms. Thus, the primary duty of the sea-water pump is indeed to circulate seawater through the cooling system, making it essential for the proper operation of marine diesel engines.