by Stephen Whitt, September 1, 2008
A Bit of History
The first submarine was powered by oars.
Submarines are ships that can operate both under and on top of the water. One of the first submersible vessels was built around 1620 by a Dutchman named Cornelius van Drebbel. We don't know that much about Drebbel's vessel, but diaries and books written at the time tell us his sub was really just a rowboat covered with a waterproof leather skin. Apparently 12 people with oars moved the vessel through the water. It could submerge to about 4.5 metres and go up to 8 kilometres before it needed to surface. It must have had some type of portholes to let in the light because one passenger wrote that people could see well enough underwater to read. Submarines have changed a lot since Drebbel's day. Today some submarines are two football fields long (200 m) and carry a crew of over 150! Nuclear powered submarines can stay underwater for months at a time. How It Works
Submarines are designed for use at great depths. Their rigid, double-walled hulls allow the crew to live and work normally underwater for as long as air and power supplies last. Submarines are steered by turning a rudder left and right. A propeller moves the sub through the water, pushing water backward so that the submarine moves forward. The crucial problem for a submarine is that it must either sink or float on command. Most things either sink or float, but can’t do both. Why? When an object is placed into water, it either sinks or floats according to its density. Objects denser than water (like metal) sink, while objects less dense than water (like air-filled balloons) float. What about a submarine?
To decend, water is pumped into the ballast tanks. To rise, air is forced into the ballast tanks, pushing the water out.
by David Garrison
Submarines are a mixture of metal (the hull), air, and water (the “ballast”). The secret of a submarine’s ability to either...