From small boats to large luxury ships, the bottoms of their hulls that are submerged in water are often painted red. What is the purpose of this?

In general, the lower part of the hull of modern ships is painted red. However, this color is not chosen randomly. This coating is essential for the operation of large ships, both for traditional and scientific reasons.

In the past, a newly painted ship, after being launched, would lose 10% of its speed within three months compared to its original speed. Ships in operation for six months would only have about half the speed they had when they were first launched.

When ships were pulled into dry docks for repairs, the entire bottom of the ship would be exposed above the water. It was then that the cause became clear: the submerged part of the ship’s bottom was covered with a dense layer of marine organisms that had attached themselves, hindering the ship’s movement. It is known that the ocean contains many types of drifting organisms such as algae, barnacles, mussels, and tube worms, which, when in their larval stage, float on the surface of the sea. Upon encountering a ship, they immediately attach to the ship’s bottom, using it as their "habitat" day after day. This is especially true in tropical seas, where these organisms are more abundant and grow rapidly. Once the hull is covered with these "inhabitants," the ship’s speed gradually decreases.

As a result, people began to paint the bottoms of ships with special paint. Initially, ships were coated with a layer of copper or lead-based paint containing copper oxide. These were considered inexpensive and effective anti-fouling agents, preventing marine organisms from attaching to the hull. The copper in the paint gave it a red color.

Later, ship painting technology advanced to the point where a variety of colors could be created. However, red remains the most popular because it has become a tradition in the fishing industry. The reason is that red contrasts sharply with the color of the sea, making it easier for sailors and fishermen to spot and assess the condition of a large ship from a distance.

In conclusion, ships were originally painted red because of the copper content, which helped kill off the marine organisms that would otherwise attach to the hull. Red is also the color with the longest wavelength, making it the most visible to the human eye, allowing any potential issues to be quickly detected.