Prince William’s wife Catherine on Thursday carried out her last solo public engagement before the birth of her first child barely one month away.

She launched the new liner the Royal Princess in the southern English port of Southampton, smashing a 15-litre bottle of champagne against its hull in a time-honoured tradition met with a cheer and a sounding of the ship’s horn.

The wind whipped at the 31-year-old’s black and white printed coat, stretched over the most famous baby bump in Britain, and the grey sky threatened rain, but she appeared relaxed as she announced: “I name this ship Royal Princess, may God bless her and all who sail in her.”

The ceremony had echoes of a cold day in November 1984 when William’s late mother, Diana, officially named the first Princess Royal. On her finger, Catherine wore her engagement ring that once belonged to Diana.

Towering above the guests, who all had some association with charities supported by Prince William, his wife and his brother Prince Harry, was the 3,600-passenger vessel, which weighs 141,000 tons and has 19 decks.

The latest ship from the Princess Cruises line, which embarks on its maiden voyage on Sunday, boasts a glass-bottomed walkway extending 28 feet (8.5 metres) beyond the edge of the ship, and claims to have the largest pastry shop at sea.

During the ceremony, which featured music from pop star Natasha Bedingfield and two military bands, a loud noise came from inside the ship’s hull. Catherine and the guests looked over, but the performance carried on.

Alan Buckelew, president and chief executive officer of Princess Cruises, said he was “incredibly honoured” to have the former Kate Middleton as the ship’s “godmother”.

The Royal Princess sets off for her maiden voyage June 16 and will sail the Mediterranean in summer, and travel to the Eastern Caribbean in the fall.