Final answer:
Propellers exposed to salt should be flushed with fresh water to remove the corrosive salt without introducing harmful chemicals or hard water minerals.
Step-by-step explanation:
Propellers exposed to salt spray should be flushed with fresh water. Salt can cause corrosion and build-up on the propeller, leading to damage and inefficiency. Fresh water is effective for rinsing away the salt spray and does not contain the minerals found in hard water that can diminish the effectiveness of soaps, making it an optimal choice for cleaning and protecting the propellers. Additionally, fresh water does not introduce any potentially harmful chemicals to marine environments, unlike other cleaning agents such as soaps or solvents.