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Monday, November 1, 2010

Navigation vs Theology

This is Royal Caribbean's Allure of the Seas, passing under the Storebaelt Bridge in Denmark. Allure, along with her sister ship Oasis of the Seas, is the largest cruise ship ever built, 360 meters (1181') long, 225,000 gross tons. That's larger than any aircraft carrier built by any navy, surpassed only by the container ship Emma Maersk and the (no longer in service) supertanker Knock Nevis.

After having lowered all of her masts and antennas, and retracting her retractable funnels, picking the one moment of lowest low water for the week and coming in at a full bell to maximize squatting, they cleared the bridge by about a foot. And then were proud of themselves for it.

Let's review, kiddies! Our tide tables are generated from gathering 19 years of data (the sun/moon/earth metonic cycle) and projecting that data forward in time. Actually in most cases this is now developed from an extrapolation of the observed tidal harmonics over a period of several months, but the point is the same; computed tides are merely a (reasonable) assumption that the height of tide will be about the same at the same point in any given 19 year metonic cycle. And, that's pretty much all the tide tables account for. They do NOT account for things like atmospheric pressure, wind, rain, sea state, whether or not some dam has opened a spillway upstream, or any other of the countless things which can effect the actual height of tide at a given moment.

Maximum speed for the Allure is 20 knots, or about 23 mph. All of her soft bendy bits had already been lowered, so if she had hit the bridge at that speed it would have been structural parts of the ship doing so. That much kinetic energy hitting the center span of a suspension bridge isn't going to end well.

UPDATE and EDIT: I had originally lambasted the master, mate and pilot of the Allure for even attempting this. However, Captain Boucher of the excellent Nautical Log blog informs me that for this particular delivery from the shipyard there truly was no other option for them. So I must humbly apologize to the bridge crew of the Allure of the Sea. And to the naval architects who designed her, I offer the only wisdom I can about shipbuilding generally: "measure twice, cut once"!

Thank you, Captain Boucher!

The full story is here: A Bridge Too Low 



When I originally posted this, I gave it a title that I thought was funny, and which implied that if prayer was a part of one's navigation plan that maybe they were cutting their tolerances too close. But, based on the number of hits this particular story has garnered (more than all of the other posts here combined), apparently a lot of people actually did want to read about theology as it relates to navigation. So at the beginning of last month I wrote what I hope will be my first, last and only post on the subject of religion. Here it is:

God, Science, the Universe and Everything

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