May 21 2009
How Does a Boat Float….
I was asked the other day, “How do submarines sink and resurface? How does a big boat float?”. Well, to explain how a boat floats, we need to travel back to somewhere around 250 BC. Yes I know there were boats before then, but the theory was explained then.
Greek Philosopher Archimedes of Syracuse described in his treatise On Floating Bodies that “a body immersed in a fluid experiences a buoyant force equal to the weight of the fluid it displaces“. So, to make it simple, its like a shoving match. The boat pushes down and the water pushes up, if the boat weighs less than the amount of water it displaces, it floats. If not, it sinks. Still confusing? Okay. Let me try it this way. Take an empty gallon jug and push it all the way under water. A gallon of water displaces about eight pounds, so you feel that upward force as you push down and try to hold it under. But if you just set it on the water surface the empty jug doesn’t displace much water so it floats. So, as far as S/V Emmanuelle goes she displaces 4617 lbs of water but she only weighs approximately 2900 lbs so she floats because the water weighs more.
A submarine, is a little different. The way they work was best described by one of the Fathers of Science Fiction, Author Jules Gabriel Verne. His description of the Nautilus, is exactly the way Subs work. The basic principle of Air is lighter than Water. A submarine has ballast tanks that are flooded with sea water to make it heavy so it sinks. When the sub reaches a certain level they stop flooding the tanks so it maintains the desired level. When they are ready to resurface, the ballast tanks are pumped full of compressed air and the water pushed out. Make sense?
I hope it does make sense, if not let me know and I will try again.
