[ExI] fermi question on poseidon adventure

spike at rainier66.com spike at rainier66.com
Tue Mar 19 22:59:05 UTC 2019

-----Original Message-----
From: spike at rainier66.com <spike at rainier66.com> 

>...OK I made up that last part but I thought of a fun Fermi question that doesn't even involve the girl:

>...What is the pressure in the propeller shaft housing when the rescuers cut into it?...spike

Here's where I was going with it.  If one estimates the pressure inside the inverted hull, a reasonable BOTEC would be just take the mass of the ship and its dimensions.  I google on passenger ship dimensions, I get:

>...The humongous Royal Caribbean's floating cities Allure and Oasis boast the whole 360 meters in length (1,181 ft), and breadth of 47 meters (154 ft), the unbelievable for a passenger cruise ship tonnage of 225,300 tons...

OK good enough, that gives about 13 tons per square meter.  An atmosphere is about 10 tons per square meter, so about 1.3 atmospheres above ambient.  But... this is a best-case.  If the ship starts to tilt with the bow lower than the stern (as it did in the original 1972 movie) then the surface area upon which the pressure acts is reduced, which increases that pressure dramatically.  Let us ignore that for now and just imagine six survivors trapped down there (including at least one you really want to ogle as much as the PG rating will allow) at 1.3 atmospheres above ambient.

We know the pressure differential on a passenger aircraft, maximum of about half an atmosphere.  The highest an airliner typically flies is around a quarter of an atmosphere and the cabin pressure is about 3 quarters of an atmosphere, so difference is about half an atm.

Now we have the six survivors down there (including the gawk bait) at 1.3 atmospheres above ambient.  How would you get them out?  You can't just cut a hole, for we know what happens when some terrorist manages to punch a hole in an aircraft: stuff gets blown out the hole.  So if they just cut a hole as they did in the movie, people and debris would come blasting out the hole with triple that amount of force, and the ship would disappear beneath the waves in a few seconds.

So... how could you get her out?  THEM rather, I meant THEM of course, ahem.  How would you get her and the others with her out of that pressure vessel?


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