How much air?

by Painter1
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DaveC426913 is offline
Aug25-11, 01:19 PM
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Quote Quote by cjl View Post
I fully agree about the danger, but at that depth, it's only going from about 2.5 atm (absolute) to 1. That doesn't change the fact that it should only be attempted by professionals though.
What's a factor of 4 between friends...
sophiecentaur is offline
Aug25-11, 05:24 PM
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To maintain the same amount of lift on its way to the surface, you would need to produce a volume around the highest point on the wreck and make it airtight but with a large hole underneath. (Effectively, an inverted bucket) This volume would need to be such that it contains the same weight of water as the boat's weight - or a little bit more. If you then pump air and fill this void, water will be displaced and the boat will rise up. As it rises, the air inside will expand but escape through the bottom - maintaining the same volume of displaced water and hence, the same amount of lift so the boat won't accelerate upwards uncontrollably. It's, afaik, normal to use lifting bags, which self vent out of the bottom and work in the way described above. Basically, you need a constant volume system and not a constant pressure system.
What do you intend to do with the wreck, once it has reached the surface? There is always the risk that it will roll when it reaches the surface and go right down again. (How big is it?)

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