On tankers, ullages are measured from which reference point?

Ullages on tankers refer to the measurement of the empty space above the liquid in a tank. This measurement is crucial for several reasons, including safety, stability, and maintaining operations within acceptable limits. The correct reference point for measuring ullages is typically an above-deck datum, such as the top of the ullage pipe.

This choice is correct because measuring from the top of the ullage pipe ensures a consistent and universally understood reference point, which is essential for accurately determining the available space in the tank. This method avoids discrepancies that can arise from varying tank structures and shapes.

In practice, using a consistent reference point like the top of the ullage pipe simplifies communication among crew members, aids in reporting and record-keeping, and ensures compliance with safety regulations. Reliable data from this reference point helps to maintain the integrity and safety of operations on board.

Other reference points, such as the tank ceiling or the tank top, may not provide a consistent measurement due to variations in tank design and the presence of cargo or sloshing liquids. Additionally, a thievage mark below the edge of the deck could lead to inaccuracies, especially if there are variations in cargo density or temperature affecting the liquid level. Therefore, measuring from an above