The correct answer is B) protect personnel from electrical shock. All electrical appliances aboard a vessel must be properly grounded to protect personnel from the risk of electrical shock. Grounding the appliances creates a safe path for excess electrical current to flow to the ground, preventing it from passing through a person's body and causing injury or even death. This is a key safety requirement specified in marine electrical standards and regulations. The other answer choices are incorrect because: A) preventing unauthorized use is not the primary purpose of grounding, C) grounding does not prevent appliances from falling, and D) grounding is not primarily about increasing efficiency but about safety.