Navy captain Nattawat Aramklua jogs, does sit-ups and other exercises for two hours every day to condition his body for Thailand's first royal barge procession in seven years. But he will not be among the 2,200 oarsmen powering the gilded vessels.

Come Oct 24, he will be the "chanterman", whose sonorous voice will guide the rowers on how swiftly or slowly to plunge their oars into the waters of the Chao Phraya River that runs through the capital Bangkok.

This 45-minute procession will be the final event for the coronation of King Maha Vajiralongkorn, who was formally crowned in May.

"If my voice is loud and strong, the oarsmen will paddle vigorously. If my chanting softens, they will slow down," he told reporters at a recent press conference. The rhythm he sets will depend on how strong the currents are on that day.

Thailand has spared no effort in preparing for this elaborate procession, during which thousands of people are expected to gather to witness 52 traditional barges being rowed in tight formation down a 3.4km stretch of the Chao Phraya.

Aboard the most important vessel, a shimmering barge called Suphannahong with a bow shaped like a swan's head, will be the King and his wife Queen Suthida.

During the main coronation event in May, the monarch, dressed in full regalia, was carried aloft a palanquin around the vicinity of the Grand Palace. This month's royal barge procession is a riverine-based version of that process, in a city where canals were so ubiquitous it was called the Venice of the East.

Thailand's 67-year-old monarch is more than a figurehead in Asean's second-largest economy.

Since inheriting the throne after the death of his revered father Bhumibol Adulyadej in 2016, he has steadily expanded his personal wealth and authority, as well as the reach of the palace.

The Crown Property Bureau, one of the biggest landowners in Bangkok, used to manage the palace's multibillion-dollar assets under the supervision of the Ministry of Finance.

In 2017, Thailand's then military-appointed legislative assembly amended the law to give the monarch full control of the bureau.

This year, new legislation exempted some of the King's properties from tax. They included "those used in state affairs, royal affairs or used by agencies under the King", according to a Reuters report.

The Business Insider estimates his wealth at more than US$30 billion (S$41.5 billion).

Earlier this month, the King ordered two army units to be put under the direct control of the palace. Through a royal decree, the soldiers and operating budget of the Bangkok-based 1st and 11th Infantry Regiments were transferred to royal security command headed by the King.

The King, who married Queen Suthida in May, raised eyebrows in July when he anointed former army nurse Sineenat Wongvajirapakdi as "Chao Khun Phra" or noble consort. In August, the palace released a series of rare photos showing the new 34-year-old consort aiming a rifle, preparing to parachute, flying a plane, as well as dressed in casual clothes next to the King.

Public criticism of the royal family is muted by a lese majeste law which makes insults or defamation of the monarchy punishable by up to 15 years in prison.

Thailand's royal barge processions, which date back over 300 years, originated from ancient naval battle flotilla, but were used in peacetime to welcome foreign dignitaries and as part of royal and religious ceremonies.

They were suspended after 1932 but revived by King Bhumibol, under whose reign 17 such processions were held. The last one took place in November 2012, to celebrate his 84th birthday.

When the flotilla next emerges on Oct 24, four ancient barges will take centre stage. The first is the Suphannahong, or Golden Swan, a 44.9m-long vessel completed in the reign of King Vajiravudh.

The Anantanakkharat, built at around the same time, features at its bow a seven-headed naga - a mythical serpent.

The Anekkachatphutchong, built during the reign of King Chulalongkorn, bears many small naga-head figurines.

And the Narai Song Suban King Rama IX features the Hindu god Vishnu riding his garuda, a mythical bird-human creature.

In the ceremony to be broadcast live on TV, King Maha Vajiralongkorn and Queen Suthida will board their barge at Wasukri Pier and alight at Ratchaworadit Pier, next to the Grand Palace.

Bangkok city administrators are preparing for the large crowds expected to gather for the spectacle. Free bus services will be provided and brochures in Thai, English and Chinese will be distributed.

Thailand's navy officers are psyching themselves up for the ceremony for which they have been preparing for a year, honing their rowing skills and rehearsing in the roughest of weather conditions.

About half of the oarsmen - specially selected for their strength - will be taking part for the first time.

They include Petty Officer Sahap hap Sompoth, 25. "I feel very proud to be part of this royal barge procession," he says. "I've always dreamed that I'd have the chance to row the boat for His Majesty."

Captain Nattawat shares his secret for the perfect performance - rest. "If I sleep for eight hours, I can sing loud enough to break glass. If I sleep any less than that, I would still be able to sing, but my voice would not be as nice," he says.