Thursday, January 19, 2012

Tall ships keel, not sink

Screen capture from BBC website
19 Jan 2012: Getting off the topic of Solar for a moment, I have been amazed at how high modern cruise ships have become, and even ferries seem high out of the water. They have shallow draft, to avoid running aground, and because tank tests must show they are stable. The Concordia is something like 14 storeys high, depending on how you count, and the draft is only 8.2m. Its impossible for the centre of gravity to be below the waterline, but the vectors from the CofG to the waterline are such that it cannot capsize, providing it is not punctured.
See this BBC page, with drawings of the ship tilting.

 They had great problems lowering the lifeboats because on the low side, the boats would be crushed by the capsizing ship and on the high side, the lifeboats would not release.
 We have all seen how the Titanic sank.... with a similar gash in the side, she gradually filled up and gracefully settled vertically into the water, taking several hours to do it, and allowing lifeboats to be launched both sides. This ship, and the Herald of Free Enterprise in the 1980s are so high that they capsize sideways when punctured, the capsize happening in a few minutes.

WTC collapse
If buildings did this, there would be a very different attitude to structure. The twin WTC towers in New York were fatally damaged, but they fell vertically, like a collapsing accordion, within their own footprint. Imagine if the impact of the planes had caused the buildings to either snap (and the upper part fall) or to fall over onto its side like a collapsing tree, or like this ship has done.

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