The Attenborough: How to put a polar ship in the water

Britain's new polar research ship is ready to go in the water. The newly minted hull of the RRS Sir David Attenborough is now standing on the slipway of the Cammell Laird yard in Birkenhead, awaiting launch day. Weather and tide permitting, she should slide into the River Mersey on Saturday. The company's David Williams told our correspondent Jonathan Amos how to put 10,000 tonnes of steel in the river.