MSC Cruises is beginning the process of "Stretching" four of its older ships
I actually have not heard this term used in a very long time since it is not as popular as it once was, but "stretching" used to be a very common way to make cruise ships bigger and hence more profitable for the company - without the need to take it out of service for a very long time.
The first cruise ship I ever sailed upon had been "stretched" - the Royal Viking Sea. I was brand new to cruising, and I had just gotten a job on the ship as a stage manager. Now here the funny thing about working on cruise ships - no one ever gives you the faintest clue on what to expect when you get onboard. I had heard the ship had been "stretched," but I was too embarrassed to ask what that meant.
I found out when I was finally aboard the ship and started walking down a long hallway with penthouses on both sides. Suddenly I tripped, they way you do when the floor suddenly gets a little bit closer than you expected. This was one of the points where the "stretching" had been done. The process left the floor a little uneven, but the carpet hid it pretty well.
Not Really Stretched
So, the term is actually just a clever word for a completely different process. Stretching a ship actually means adding a new mid-section to the existing ship. Yes, they have to cut the existing ship into two separate pieces - and then they insert the new, pre-built section between them and weld the entire ship back together again.
It's a little like remodeling a house - but the beauty of ships is that they float, which makes the entire process of moving the separate parts around a lot easier.
In fact, ships are built as a series independent water-tight sections, to reduce the possibility of sinking. To sink, a ship must lose its buoyancy by displacing air with water. If you can build a ship so any damage to the hull will only result in a small percentage of the entire vessel taking on water, you vastly reduce the possibility that it will sink.
Even the Titanic and Concordia were built with water-tight compartments, but in both cases several of these compartments were breached. The ice berg ripped a long gash in Titanic, while the underwater rock of Giglio also ripped a long gash in the hull of Concordia. This is the reason those ships sank, and the same reason any many other ships can survive damage to the hull and still sail safely.
Why am I mentioning this? Because the process of "stretching" a ship involves making the cuts at the point where the water-tight section sections meet. Then the separated pieces can still float on their own, because they maintain buoyancy. The same is true of the new section being added - it is also a water-tight section that can float on its own.
And so the process of stretching a ship goes like this:
The steel hull of a ship, and everything above the hull, is cut along the lines of the water-tight sections. This is done in a "dry-dock" - an area that resembles a "lock" to raise ships between two different water elevations. A "dry-dock" has lock gates at each end so a ship can sail into the dry-dock, then the gates can be shut and the water and can be pumped out. This leaves the entire ship on dry land - an incredible sight to see, but one that it is done rather commonly.
Such is the construction of cruise ships that they are balanced enough to remain in the same upright position resting upright on their keel (the solid steel weight below the hull that extends all the way from the pointing bow of the ship to the propellers at the stern). The keel distributes the bulk of the ship's weight to the lowest point of the ship; adding stability to the vessel. In the dry-dock the keel sits atop huge wooden blocks that can obviously take an incredible amount of weight, which is a testament to the sturdiness of trees in nature.
A dry-dock is used so the workers can cut all the way down through the keel. Once the two parts are fully separated, each side is shored up so it is completely water-tight again, and then the "dry-dock" is refilled with water.
At that point, the new section of the ship is floated into the water-filled dry-dock and directed into place. Enough welds and rivets are placed the make the ship solid once again, and then the dry-dock is once again drained. The workers finish the job by sealing up both sides of the new section and connecting all the cabling, laying carpet, etc.
The MSC Armonia Stretching
The Armonia is in the process of being stretched right now, and soon the same process will be done to the MSC Lirica, MSC Sinfonia and MSC Opera. The cost for each ship is €200-million, a lot of money but significantly less than building an entire new ship (which MSC also has on order). After the “stetchings,” each ship will be 275 meters long, weigh 65,000 tons and will carry 2,680 berths, boasting 193 additional cabins (plus 59 new cabins for crew members).
Here are the pictures to show the difference: before... and after