(CNN) — Couple person-made movable constructions are much larger than a modern cruise ship, but even these giants of the sea in some cases have to have a person to lend them a hand to get to port.

So what do you do when one particular of these giants of the sea is not able to shift on its have ability?

You simply call a ship-carrying ship, or, to be more exact, a “semi-submersible hefty transportation vessel,” this kind of as the Boka Vanguard.

Constructed in 2012, the 275-meter-very long Boka Vanguard is the biggest ship of its sort. Normally it transports substantial offshore oil and gas constructions, but occasionally it will be termed on to to have other vessels — these types of as transpired with the Carnival Vista back prior to the pandemic.

The Carnival Vista is the second largest in Carnival’s fleet, with ability for 4,000 passengers and 1,500 crew, and in July 2019 it essential rescuing following enduring a malfunction in Caribbean waters.

Cranes are not actually an possibility when you will need to lift a 133,500-ton ship out of the h2o (the premier cranes in the entire world raise about 20,000 tons), so the Boka Vanguard uses a relatively distinct technique.

Float-on/float-off

This peculiar-on the lookout vessel has a flat, open up central deck — entirely vacant — with five big vertical wall-like buildings protruding from its sides. The control bridge and the crew’s living quarters are nested in one of them, which is substantially bigger and taller than the other four.

The ship’s awkward condition hides a sophisticated system of ballast tanks that makes it probable for it to turn into semi-submerged, with only the major of the vertical structures remaining above drinking water. Distinctive kinds of floating cargoes, like complete ships, can then slide on to its deck to be appropriately fastened. This is referred to as the “float-on” operation.

After the cargo has been secured on deck, the ballast tanks can be emptied for the Boka Vanguard to arise all over again from the h2o, lifting its heavy cargo upwards with it. It can then begin its journey just like any other ship. When it has arrived at its intended desired destination, the procedure is reversed. This is the “float-off” stage.

“We simply just just take gain of Archimedes’ legislation to raise some huge cargoes,” claims Michel Seij, world wide engineering normal supervisor at Boskalis, the Dutch company that owns Boka Vanguard. You might keep in mind the Archimedes theory from the “Eureka!” story — any entire body submerged in fluid is acted on by an upward pressure, with a magnitude equal to the bodyweight of the fluid displaced by the physique.

The oil and gasoline business

Boskalis ships, for example, have assisted in the transportation of two US Arleigh Burke Course destroyers following they were both broken in two different collisions with service provider ships in Asian waters in 2017, USS Fitzgerald (DDG-62) and USS John S. McCain (DDG-56). Despite the fact that on that situation it was not the Boka Vanguard, but two lesser semi-submersible weighty elevate ships, the Transshelf and Treasure respectively.

Ship-carrying is just not among the most popular assignments for this type of ships. The bread-and-butter get the job done is shifting platforms and weighty tools all-around the world’s significant offshore oil and fuel fields. But you never know.

In the scenario of the Carnival Vista, the have to have to phone in the Boka Vanguard arose when the ship’s propulsion system malfunctioned and the only dry dock in the location wasn’t available. An different solution experienced to be identified.

“We have been termed in at small discover, but we managed to dispatch the ship rapidly. It took a few of weeks for our ship to get to the Caribbean from Europe and yet another week to consider treatment of all the essential arrangements. What followed was a really clean operation and the cruise ship was properly transported to Freeport, Bahamas. During this operation component of the cruise ship’s crew remained on board,” says Seij of the Carnival Vista dry-docking operation.

The Boka Vanguard is not only the premier ship of its kind, making it achievable for it to easily consist of the 325-meter-extensive Carnival Vista within just its composition, but it can also be employed as a going dry-dock, producing it doable to conduct routine maintenance on the ship while underway or in port.

This was the situation with the Carnival Vista, a clockwork procedure assisted by several lesser vessels, that has presented us with mesmerizing footage of the entire sequence.