The yacht maintenance business has been jumping. MB92, which also owns a smaller yard in La Ciotat, France, reported revenue of €191 million (about $215 million) in 2021, up from €150 million in 2019.

Even if a superyacht is a striking showcase of wealth, owners expect those working for them to keep silent about their assets and whereabouts. When asked about the Sea Rhapsody’s destination once it left the yard, Henk Dreijer, the commercial director of MB92, demurred, suggesting that it was bound for “the Caribbean, but it could also be the Seychelles or somewhere else.”

“We work for people who like to be very discreet,” he added.

In Barcelona, which is led by a left-wing city government, not everybody welcomes the arrival of billionaires and their yachts, whose marinas are typically fenced off from the rest of the city’s waterfront.

“We are bringing in the richest people in the world, but they don’t spend their money in our local neighborhoods, they have yachts that fly the flags of tax havens, and they hire crews who are not from Barcelona,” said Gala Pin, a city lawmaker in Barcelona until 2019.

“We have also allowed private and very opaque companies to squeeze profits from public land and instead fence off access to a port area that should be enjoyed by all the citizens of Barcelona,” she added.

A decade ago, Ms. Pin and other residents held demonstrations to protest the initial project to develop Port Vell, a privately owned marina for luxury yachts. But Ms. Pin now concedes that the yacht business is very firmly anchored in Barcelona. Meanwhile, the city’s dwindling fishing fleet is squeezed into a small enclave, sandwiched between MB92’s yard and the superyacht marina.