One of the unique features of a ship is the round windows or portholes as they are more commonly known. The circular openings are called portholes and the glass covers are called port lights. Porthole is the shortened form of the word ‘port-hole window”. Portholes are not only found on ships, they can also be found in submarines and spacecrafts.
So why do ships not have square or rectangular windows? It is mainly due to structural integrity. The ocean puts a lot of pressure on the body of the ship and square windows are more susceptible to stress. Rectangular or square windows tend to be weaker in some spots as compared to others. A round design is logically tougher and easier to reinforce. The unique round design of the ship portholes offers resistance from sunlight, and also from the sea and rain water.
The materials generally used for portholes are brass and bronze because as compared to iron and steel brass and bronze don’t rust due to the sea water. One disadvantage of steel is that it will bend after some time.
Not all ships have portholes. Large cruise liners have much higher structures and their upper deck cabins are really high and they boast large windows and even balconies.