Yes, it is reinforced concrete. You might be surprised, but reinforced concrete vessels were quite popular at one time. The first reinforced concrete boat was built in 1855 by an engineer Jean Louis Lambo at the Paris World Expo. By the beginning of the twentieth century, there were more than one hundred such ships.
Although these holes were a bit too much fuel, they were common. After the end of World War II, they were produced less and less. However, there are still thousands of survivors. reinforced concrete freaks plying water arteries around the world (especially if it is the third). We also have them there.
The defenseless miscarriages of shipbuilding.
Reinforced concrete ships – a dead-end branch of evolution. But pretty!