Over and under!

Over and under!

Most boats travel through the water - a good part of the boat (the hull) is under water, and the rest is above the water.

But some boats are a bit different.

A hovercraft, like this one, actually moves OVER the water. It sits on the water when it is still, but when it moves, it pushes out a cushion of air that lifts it just above the water. The air is kept in by the "skirt" around the edges.

Other boats move around completely under the water.

A submarine can move along the surface of the sea, but when it closes all the hatches, it can dive down, and move along under the water.

Sub means under, and marine means sea - and that is how a submarine got its name.

Submarines are very cramped inside, because there is not much room.

If you want to have a look at some movies of what a submarine in World War II was like (remember, that was nearly sixty years ago), try going to this site.

These days tourists in places like the Great Barrier Reef can go down under the water in a craft called a submersible.

It lets you look at the fish and the coral from close up, without getting wet!