SO I finally saw this movie and I really liked it, I love when action movies throw in the one-liners and sarcastic remarks, it's good not to take themselves to seriously.
And about the underwater boat, are you talking about when they were walking on the bottom of the ocean with a canoe over them? Well, I know what they did probably wouldn't work, but it's semi-feasible when you think about early diving bells. Get a bowl of water and turn a glass upside down and press down. There's still an air pocket in there, I don't know the phsyics or anything when done with a canoe, but it's something to consider.
Denis Papin
Many different diving bells were tried over the years. They all had the same problem in common: How do we get fresh air down to the bell ? The Frenchmen Papin came with the solution in 1689. He designed a diving bell that was supplied with fresh air through flexible hosepipes and bellows. A truly fantastic idea but there was one slight little problem: The bellows of his time did not have enough strength to press the air down to the bell. Bummer.....
Edmund Halley
The English scientist Edmund Halley came up with a different solution in 1690. He invented a way to force pressurized air down to the bell. Why does this air have to be pressurized ? Take a glass, hold it upside down and push it down in a bucket of water. The water pressure will press the amount of air together. This happens also when you lower a diving bell in the water. Every 10 meters the pressure will go up by 1 atm/bar. When you lower a 3 meter high diving bell to 200 meters, the remaining layer of air inside the bell will be about 15 centimeters ! Halley attached empty barrels to the diving bell. A hole in the bottom of these barrels let in water. The barrels were attached to the diving bell by flexible hoses. The divers could let the air in by turning a faucet. The pressure was equal to the amount of water moved by the bell. In this way, the pressure inside the bell stayed the same as the surrounding water. Halley tried his invention several times. He stayed below at 20 meters depth for more than 1.5 hours without suffering any bad consequences. Halley also came up with small bells to fit over the divers head, with air supply from the diving bell. However, he soon found out that it was not possible to breath in the surrounding high water pressure. John Lethbridge came up with the first armored diving suit. Have a look at the Armored Diving Suit section to learn more about this.
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