1. Heavy steel ships float because of hollow space and air. Even though a small steel nail sinks immediately in water, a gigantic steel ship floats because its hull is mostly filled with empty air. The hollow shape makes the overall boat lighter than the amount of water it pushes out of the way (buoyancy)!

2. Submarines dive by swallowing ocean water. To sink underwater, a submarine fills special double-walled compartments called ballast tanks with heavy seawater. When it is time to surface, the sub pumps compressed air into the tanks to blast the water back out, making the ship light enough to float up!

3. The world's oldest surviving boat is over 10,000 years old. Discovered in the Netherlands, the Pesse canoe was carved out of a single hollowed-out pine tree trunk using stone tools long before metals like bronze or iron were even discovered!

4. Ships speak to each other using colorful signal flags. Before radio communication existed, sailors hung rows of bright geometric flags called the International Code of Signals from ship masts to send messages across the open sea, like warnings about storms or requests for medical assistance.

5. Boat directions have special nautical names. Sailors don't say "left" or "right" because those directions change depending on where you face! On a boat, the front is the bow, the back is the stern, the left side is port, and the right side is starboard.

6. Cruise ships are like giant floating cities. The world's largest cruise ships can hold over 7,000 passengers and 2,000 crew members. They feature full-sized ice-skating rinks, water parks, outdoor parks with thousands of real trees, and their own water desalination plants to make freshwater out of seawater!

7. Hovercrafts float across water on a cushion of trapped air. A hovercraft uses powerful fans to blow air underneath a rubber skirt, creating a high-pressure bubble that lifts the vessel entirely off the surface so it can glide smoothly over water, ice, mud, or land!