Sir David Attenborough polar ship set for launch

It should make for quite a splash!

The 10,000-tonne hull of the UK's new polar ship will be put in the River Mersey later - around 12:20 BST.

Named after the TV naturalist Sir David Attenborough, the vessel has been assembled at the Cammell Laird yard in Birkenhead and placed on its slipway.

The broadcaster himself will be asked to unleash his steel namesake - pushing the button that sends the hull sliding down wooden rails which have been caked in thick grease.

The hull will go in stern-first and should create a big wave as it bites the water just as the Mersey reaches high tide.

Cammell Laird has had the riverbed dredged in front of its slipway to make sure the steel mass does not bottom out.

Saturday is an important milestone for the ship, whose development has been followed closely since an online campaign tried to get it named "Boaty McBoatface".

Ministers intervened to insist on a more appropriate name - but that has not dampened the interest in what is the largest commercial ship to be built in Britain in three decades.

"She's like a giant Airfix model," said Cammell Laird project manager John Drummond. "She's being put together with one million pieces of steel, 30km of piping, 5,000 valves, and 450km of cabling."

The steelwork going in the water represents the lower-decks of the Attenborough and the components whose great size meant they had to be encapsulated during the build. This included the vessel's huge diesel-electric Rolls-Royce engines.

Tugs will be on hand to catch the hull as it floats out into the Mersey. They will then move the structure to the company's "wet basin".

It is here that the upper-decks will be attached, together will all the internal fixtures and fittings, such as cabins and laboratories.

"At the moment we have just the six decks in the hull, and the other six decks of what we call the super-structure will be lifted on after she's gone into our harbour," explained Claire Biggar, assistant ship manager at Cammell Laird. "I'm so excited at the prospect of seeing her slide into the Mersey with the Liverpool backdrop. It should be an amazing day."

An official handover of the finished ship is scheduled for the end of the year. It is at this point that the RRS Sir David Attenborough can begin sea trials, and go on its maiden expeditions to the Arctic and the Antarctic.

"One of the main trials we have to do is in sea-ice," said Captain Ralph Stevens from the British Antarctic Survey. "We'll take her up into the Arctic and test her performance in the floes and that will give us a really good yardstick to know how far we can push this vessel. Her first year, 2019, is really a rehearsal year when we test everything onboard. In 2020, she'll be fully operational," he told BBC News.

Why does this matter?
The two ships that make up the UK's existing polar fleet - the RRS James Clark Ross (JCR) and the RRS Ernest Shackleton - are ageing, with nearly 50 years' service now between them. These vessels are also getting expensive to run. The £200m, state-of-the-art Attenborough will be their replacement. It will have the capability to fulfil all the roles currently undertaken by the JCR and the Shackleton, which broadly split into research and logistics.

How will the Attenborough be used?
The new ship will support scientists working at both ends of the planet. At times, this will include delivering the supplies that sustain British bases, such as Rothera and Halley in Antarctica. On other occasions, it will mean acting as the platform from which scientists can launch investigations of the polar environment. Because of where the ship it will have to work, the hull has been designed to break through metre-thick sea-ice.

How special is the ship?
The Attenborough will be equipped with all the latest scientific gear. It will have a helipad, cranes and onboard labs, and have the ability to deploy subs and other ocean survey and sampling kit. One of its key features is an enclosed "moon pool". This is essentially a huge hole running right through the middle of the hull. It will allow instruments to be lowered into - and recovered from - the sea when weather or dense sea-ice conditions would normally make such work very difficult. The ship design, put together by Rolls-Royce, also enables near-silent running when required, meaning scientists can study sea creatures without disturbing them.

What happened to the "Boaty" name?
Boaty McBoatface lives on in the form of a yellow submarine. The National Oceanography Centre in Southampton has three long-range autonomous underwater vehicles. When one of these is out on patrol, it carries the humorous moniker. The intention is that these Boaty-class subs will frequently operate from the Attenborough. They will be asked to go into places the ship itself cannot reach. A good example would be the colossal ice shelves that surround Antarctica. These are floating slabs that are hundreds of metres thick and the only way to explore their undersides is to use an autonomous vehicle.