Porthole

A porthole is like a window on a ship. It is round and it is usually found on the side of the ship near the water. It is made of metal or glass and has a cover that can be opened or closed.

When the ship is sailing, the porthole allows fresh air to come inside and it helps to keep the ship well-ventilated. It is also used to let in sunlight and give the people on the ship a view of what's outside.

The cover of the porthole is to keep water out when the sea is rough or if there is a big wave. It's like closing your eyes when water splashes on your face - it keeps the water out of your eyes.

So, in short, a porthole is a window-like structure that helps keep a ship well-ventilated, allows sunlight and a view of the outside, and keeps water out when there are big waves.