What do cruise ships do when they need to hitchhike

(CNN) – Few man-made mobile structures are larger than a modern cruise ship, but even these giants of the sea sometimes need someone to lend a hand to get them to port.

So what to do when one of these sea giants is unable to move on its own?

You call a boat-carrier, or, to be more precise, a “semi-submersible heavy-lift vessel,” like the Boka Vanguard.

Built in 2012, the 275-meter-long Boka Vanguard is the largest vessel in its class. Typically, it carries large offshore oil and gas structures, but it will occasionally be called upon to transport other vessels – as happened with the Carnival Vista before the pandemic.

The Carnival Vista is the second largest in Carnival’s fleet, with a capacity of 4,000 passengers and 1,500 crew members, and in July 2019, she was in need of rescue after suffering a malfunction in the waters of the Caribbean.

Cranes aren’t much of an option when you need to lift a 133,500 ton vessel out of the water (the largest cranes in the world lift around 20,000 tons), so the Boka Vanguard uses a pretty different approach.

Floating / floating

This peculiar-looking ship has a flat, open center deck – completely empty – with five large vertical wall-like structures protruding from its sides. The control deck and crew living quarters are tucked away in one, which is considerably taller and taller than the other four.

The ship’s awkward shape hides a complex ballast system that allows it to become semi-submerged, with only the top of the vertical structures remaining above the water. Different types of floating cargo, including entire ships, can then slide across its deck to be properly stowed. This is called the “float-on” operation.

Once the cargo is stowed on the deck, the ballasts can be emptied so that the Boka Vanguard comes out of the water again, lifting its heavy cargo with it. It can then begin its journey like any other ship. When he arrives at his intended destination, the process is reversed. This is the “float” stage.

“We are simply taking advantage of Archimedes’ Law to lift massive cargoes,” explains Michel Seij, managing director of global engineering at Boskalis, the Dutch company that owns Boka Vanguard. You may remember Archimedes’ principle of “Eureka!” history – any body immersed in a fluid undergoes the action of an ascending force, of a magnitude equal to the weight of the fluid displaced by the body.

The oil and gas industry

Boskalis ships, for example, helped transport two US Arleigh Burke-class destroyers after they were both damaged in two separate collisions with merchant ships in Asian waters in 2017, the USS Fitzgerald ( DDG-62) and USS John S. McCain (DDG-56). Although on this occasion it was not the Boka Vanguard, but two smaller semi-submersible ships, the Transshelf and the Treasure respectively.

Transporting ships is not one of the most common tasks for this type of ship. The basic job involves moving rigs and heavy equipment around the world’s major offshore oil and gas fields. But you never know.

In the case of the Carnival Vista, the need to call in the Boka Vanguard arose when the ship’s propulsion system malfunctioned and the only dry dock in the area was not available. An alternative solution had to be found.

“We were called in at short notice, but we were able to get the ship out quickly. It took our ship a few weeks to get to the Caribbean from Europe and another week to make all the arrangements. worked very well and the cruise ship was transported safely to Freeport, Bahamas. During this operation, part of the crew of the cruise ship remained on board, ”said Seij of the Carnival Vista dry dock operation.

The Boka Vanguard is not only the largest vessel of its kind, allowing it to comfortably contain the 325-meter-long Carnival Vista in its structure, but it can also be used as a mobile dry dock, allowing for maintenance. ship en route or in port.

This was the case with the Carnival Vista, a clockwork operation assisted by several small vessels, which provided us with fascinating images of the entire sequence.

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