Royal Caribbean International followed a long time maritime tradition on Thursday to commemorate the start of construction of the fourth vessel in its super-sized Oasis-class of cruise ships. (Image - Royal Caribbean - click on image to enlarge)

A keel-laying ceremony was held at the STX shipyard in St. Nazaire, France, where the 5,400-passenger ship is being built, Royal Caribbean said in a news release.

As part of the shipbuilding ceremony, a 1,000-ton block of steel was lifted by crane into the building dock for work to begin, and newly-minted coins were placed under the keel — the nautical term for the ship's foundation or spine.

When completion of the cruise ship draws near, the coins will be retrieved and presented to its captain and crew to be placed onboard as a memento to bring it good luck.

The yet-to-be named Oasis ship will be delivered in spring 2017, according to the Miami-based cruise operator.