What is the difference between the Tropical Draft Mark and the Summer Draft Mark?

The Tropical Draft Mark is established to indicate the maximum draft to which a ship is permitted to load when operating in tropical waters, where water density is typically lower due to higher temperatures. Consequently, to account for this reduced density, vessels are marked to show a deeper draft for safe operation in these warmer waters.

On the other hand, the Summer Draft Mark indicates the maximum allowable draft for vessels in temperate waters, where the density of seawater is higher, primarily because of lower temperatures. Thus, the Summer Draft Mark is positioned higher than the Tropical Draft Mark. This is because vessels typically displace more water in colder, denser water conditions compared to those in warmer, less dense conditions.

Therefore, the Tropical Draft Mark is above the Summer Draft Mark, reflecting the adjustments made to ensure vessel safety and stability depending on the water conditions. This distinction is crucial for safe navigation and ensuring compliance with international maritime regulations.