Question 36 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is A **Explanation for Option A (Correct Answer):** Draining a saltwater ballast tank located **above the waterline** can be accomplished without the use of a ballast pump due to the principle of gravity. When the discharge valve or line leading from a tank located above the ambient water level is opened, the hydrostatic pressure of the water inside the tank is greater than the pressure outside, allowing the water to flow out naturally and overboard. This process is known as gravity discharge or gravity deballasting. **Explanation for Incorrect Options:** **B) Draining a saltwater ballast tank located below the waterline:** If a tank is located below the waterline, the ambient water pressure outside the hull (at the discharge point) is greater than or equal to the pressure of the water inside the tank. Therefore, gravity cannot overcome the external pressure, and a ballast pump (or sometimes compressed air, though a pump is standard) is required to forcefully push the water out. **C) Filling a saltwater ballast tank located below the waterline:** Filling any tank requires overcoming resistance, which is usually accomplished by a pump. While some tanks can be filled passively using gravity intake (i.e., just opening the sea chest and allowing water to flow in when the tank is empty and the inlet is below the waterline), this operation is the **opposite** of deballasting (which means emptying the tank) and thus does not fit the context of the question ("deballasting operations"). **D) Filling a saltwater ballast tank located above the waterline:** This operation is the **opposite** of deballasting (like Option C). Furthermore, lifting water from the sea chest (which is always below the waterline) up to a tank located above the waterline always requires mechanical energy, meaning a ballast pump is essential to overcome the vertical head.