Tuesday, July 04, 2006

Tony Robinson's Titanic Adventure

Considered unsinkable, SS Titanic was technologically and aesthetically a state of the art ship. Bound for New York on her maiden voyage from Southampton on 10 April 1912, she represented the largest moving manmade object of her time. However, just five days later, the great ship lay two miles below the surface of the North Atlantic. The public were shocked. It seemed impossible that such a fate could befall the 'unsinkable' ship and for many years mystery surrounded the precise reason for her sinking.
Some details of her tragic end have always been known though. Travelling at 24mph, almost top speed, Titanic had struck an iceberg on her starboard hull. Within three hours the ship had sunk, 480 kilometres southeast of Newfoundland. Of the 2223 people onboard, 1517 perished.
Considering the time she took to sink and eyewitness reports suggesting that the ship broke in two, most investigators concluded that Titanic sustained a huge gash in her side, perhaps up to 100 metres long. But these conclusions were inconsistent with reports from other survivors who felt and heard little or nothing during the collision.
Since her resting place was discovered in 1985, technology has advanced and enabled some light to be finally shed on the mystery of precisely why Titanic sank.
Staying afloat
To understand why Titanic sank, it helps to understand how ships float. Archimedes is credited with discovering how an object floats on water. In Syracuse, Sicily, in the 2nd century BC, the Greek mathematician had been pondering the question, when, reputedly, the answer came to him in the bath.
As he climbed into the tub, he noticed the water level rise. He realised that a floating object must be buoyed up by a force. The force is a consequence of the water pushing on the object – a result of the object being pushed down under its own weight by gravity. More precisely, if something is to float, the force buoying up the object must equal (or exceed) the weight of water the object displaces. Put another way, the weight of water the object displaces must be equal to, or more than, the weight of the object. When this happens the force pushing on the object is great enough to keep it afloat.
The hull of a ship is designed to have great volume, and so is able to displace a considerable weight of water; a weight that's typically much greater than the weight of the boat – hence it floats! Titanic weighed in at 42,028 tonnes, but the ship's hull was designed to displace 59,874 tonnes of water. So, applying Archimedes' principle, it's easy to understand why Titanic floated – it displaced 17,846 more tonnes of water than it weighed.
Why she sank
Until recently, why Titanic sank was a mystery. During a number of expeditions to the wreck in the 1990s, a team of scientists fired sound waves at the remains of the hull, buried in the soft seabed sediment. The sonar images revealed, for the first time, the damage caused by the iceberg.
What the images revealed was a great surprise – there was no trace of the supposed 100-metre gash. Instead, they showed a series of small breaches, the total area of which was tiny, less than one square metre, compared to the size of the ship. As unbelievable at it may appear, this seemingly minor damage led to the demise of the great ship.
Titanic was divided into 16 compartments along the length of her hull, each separated by a bulkhead that rendered them watertight. The flooding of one compartment alone would not have been enough to sink the ship, since the volume of each compartment equated to a displacement of approximately 3600 tonnes of water and the Titanic would need to take onboard 17,780 tonnes of water before she would lose her buoyancy and sink.
But as fate would have it, when the ship scraped against the iceberg, a number of relatively small holes punctured six of the compartments – each would have filled with water. Six multiplied by 3600 tonnes meant that 21,600 tonnes of water had gushed into her hull, well over the 17,780-tonne critical limit.
So it was not the size of the breaches that spelt doom for Titanic, it was their number and position. Had only two or three compartments flooded, the ship would probably have remained afloat.


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