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Interesting question.
Wikipedia suggests 70% efficiency. Not bad.


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sapere aude
by Number 6 on Wed Oct 24th, 2012 at 08:24:03 AM EST
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Oooh, cool option: a giant underwater balloon!

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sapere aude
by Number 6 on Wed Oct 24th, 2012 at 08:25:28 AM EST
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