interesting factoid

Here is a factoid that I ran into while interning at a shipping company a few years ago. To my dismay, none of the colleagues found my little discovery interesting. (The level of curiosity and intellectual drive is quite low in these sectors.)

Fact

A chemical tanker burns the same amount of fuel no matter whether it is loaded or not. (Note that this statement is completely false for trucks, planes etc.)

Some Speculative Explanations

- As a ship is loaded with more weight, its depth below the water line increases. This allows the vessel to go straight through the waves rather than riding over them, and thereby decreases the actual distance travelled to reach the destination. Despite the heavier weight being pulled, the fuel consumption does not change due to this added efficiency.

- A propeller works by pushing out water particles and thereby creating a conic spiral wave behind the ship. The top of this cone is always horizontally cut out since the water particles have nowhere to go when they reach the surface. When a ship is loaded, it propeller gets further away from the surface. In other words, the mentioned cone becomes larger, and the push generated becomes greater. This results in higher fuel efficiency.