Ullage measurements are taken from the top of the liquid to which location?

Ullage measurements are crucial in determining the amount of liquid in a tank and are commonly conducted from a reference point to the surface of the liquid. The correct choice denotes that ullage is measured from an above-deck datum, typically the top of the ullage hole. This method provides a consistent point of reference that is easily accessible and allows for accurate and reproducible readings.

When starting from the top of the ullage hole, it ensures that all measurements are uniform and standardized, which is essential for effective inventory management and safety procedures on tankers. This approach aligns with industry practices as it minimizes variations in measurement techniques that might occur if different reference points were used.

Other locations, such as the base of the expansion trunk, the base of the ullage port, or a line within the ullage port, can result in discrepancies due to factors like tank design or position of the liquid. These options could lead to inconsistencies in readings and might not provide a reliable baseline for determining the ullage accurately.