Royal Caribbean will expand its Oasis-class with a fourth ship, which is expected to launch in 2018.

The new vessel will share the title of ‘the largest ships in the world’ with the line’s Oasis of the Seas, Allure of the Seas and a third unnamed ship, which is scheduled to launch in 2016.

The third and the fourth Oasis-class ships will have 16 decks and 2,700 staterooms.

They will feature seven themed areas and the Oasis-class ‘first’ at sea activities such as the 82 foot-long zip line, a handcrafted carousel, the AquaTheatre high-diving performance venue and the Central Park with more than 12,000 live trees and plants,

There will also be twin FlowRider surf simulators, whirlpools, an ice-skating rink, the H2O Zone kids aquapark and the Royal Promenade – a boulevard of shops, restaurants and lounges.

Chairman and chief executive Richard D. Fain said the additional Oasis-class vessels reflect the success and customer satisfaction from Allure and Oasis.

The announcement was made at the keel-laying ceremony for the third Oasis-class ship at the STX shipyard in Saint-Nazaire, France.

The keel laying of the third Oasis-class ship marks an important milestone in the development of the ship, as it signifies the beginning of its physical construction.

During the ceremony, a 1,000-ton block measuring 10 x 47 meters was lifted by crane into the building dock.

Newly minted coins, which are said to bring luck to the ship during construction, were placed under the keel and will stay in place there until the end of the ship’s construction.

Once the ship is near to completion, the coins will be retrieved and presented to the ship’s Captain and crew to be placed onboard the ship.