How do you build a hull - Q & A
Just 93 working days after Honfleur's keel-laying ceremony on August 6, her completed hull will slide backwards with a splash into the Baltic. This mighty structure will be 187 metres long and 31 metres wide, almost completely filling the vast berth in which it is being built. It will be six decks and 20 metres high, and will weigh 10,000 tonnes, including the engines, motors and propellors which will also have been fitted in that time. But how do you create such a colossal, complex structure so quickly? The answers: plan every weld, start well in advance, split the hull into slices, and do some of it upside down.
How much of a ship can be made in advance of the keel being laid?
Quite a lot. Between the ceremony to mark the first steel cut for Honfleur on March 12 and her keel-laying on August 6, thousands of tonnes of steel was cut and welded into dozens of sections of hull, each weighing up to 220 tonnes. "It's just a question of time and space," says Anna-Lena Bubenheim, Project Manager for Honfleur at FSG, the German shipyard where she is being built. "We have one building berth, and it's not efficient to have one vessel occupying it for the whole time its steel is being cut and welded." In total, 118 sections will be prefabricated and craned onto the slipway to create the hull, meaning Honfleur will grow by hundreds of tonnes most days.
Why build in sections?
Creating a ship like Honfleur is the opposite of baking a cake: you make the slices first, then put them together. "It's faster, more efficient and more manageable this way," explains Anna-Lena. "We can have small teams of workers go into the individual sections to complete their specialist tasks without getting in each other's way. Having open ends to the sections makes it so much easier to get large or long components in, such as pipes. And as many of those pipes are carried overhead it's often easier to build a section upside-down and not have to lift the pipes to attach them. We can just flip it over once it’s finished."
How are the sections joined?
Once the sections are complete they're lifted by the dockyard crane, placed on a trailer and driven (very slowly) to a paintshop the size of an aircraft hangar. They're given four coats of paint, but the edges of the sections are left bare for welding. Then they're driven to the slipway. Shipbuilders like to talk about how they 'make steel swim', but first they make it fly, lifting sections weighing as much as five fully laden articulated trucks high into the air and over the existing hull to the required spot. Teams of highly skilled shipbuilders then align the sections with millimetric precision despite their huge weight using chains and hydraulics. They're then welded, and the pipework connected and paint completed. "Of course there are lots of tasks such as cable-pulling and completing the engine installation which can only be done once the hull is complete," says Anna-Lena. "But by doing everything else in advance, we give those teams more time."
How do you get 10,000 tonnes of steel into the sea?
Easy - just let it slide in. There's a bit more to it than that, of course, but the FSG shipyard has Germany's only remaining traditional slipway, in which a hull (or complete ship) is launched backwards into the sea. The slipway itself is a wooden platform about 2.5 wide which runs down the centre of the building berth. The hull rests on steel and concrete supports across its entire beam while being built. But once complete, the slipway is raised up to take the entire weight, the other supports are removed and the hull balances on its centre line. The sea doors at the end of the berth are opened and the water comes around a fifth of the way up the vessel: not enough to float it. The restraints holding the slipway in place at the sea end are removed (and a hydraulic ram gives it a shove at the top if required) and the hull and slipway slide together into the Flensburg fjord. "This is when we see if it actually swims," jokes Anna-Lena. "It's an amazing sight. I've seen six launches since I've been working here and it could never get boring."
This is only how Honfleur's hull is constructed. After launch her entire superstructure must be fitted, with her remaining five decks, her bridge, her passenger areas and 261 cabins. It's just as impressive a process, and deserves its own explanation.