I assume they must be attached to some kind of mechanized bicycle chain, but no, he's simply rowing with his legs, looking as comfortable as if he were watching TV while pedaling an exercise bike.
A woman in a conical hat squats on the very bow of the boat.
As they pass our mighty ship, a replica of a colonial river steamer, they both stare up in curiosity.
From the top deck I offer a wave and they break into big smiles as the man lifts both arms aloft, proudly advertising the fact that he can row with no hands.
It's one of many charming sights I witness as I cruise up Vietnam's Red River, considered the cradle of Vietnamese civilization.
"In North Vietnam we have an expression," says our guide Duoc -- or Duke, as his badge reads. "The Red River is our mother's milk."
Over the next 10 days he recites many a historical anecdote as we sail on the RV Angkor Pandaw from the magnificent Ha Long Bay up the Red River to Hanoi, and into the clear rustic waters of the Da River, a journey of more than 600 kilometers.
Our captain is Duc Doc, a local North Vietnamese who, perhaps unsurprisingly, cut his teeth on this network of waterways by piloting a cargo boat for three years.
"The lower part of the river is not so beautiful," he says.
"There's a lot of traffic, and it can get very misty in the winter months. Fortunately we have radar to detect any sandbars or obstacles."
Nonetheless, on day five of the journey, we get stuck in a sandbar, such are the shifting sands of the current. The captain reverses to get us out.
"So far, I've never needed to call in a tugboat," he says with a smile.
Spectacular Ha Long Bay
The genius of these replica paddle steamers is the shallow draft -- only 1.2 meters.
It means these flat-bottomed boats can navigate uncharted waters with a decent degree of confidence, and can still navigate upstream or downstream in the dry season when the water levels are at their lowest.
Duc Doc says his favorite part of the trip is Ha Long Bay, a spectacular labyrinth of karst cliffs that thrust out of tranquil waters off Vietnam's northeast coast.
These gigantic rocks are 25 million years old, and one of Asia's most photogenic natural wonders.
We spend the first night and entire next day of the cruise here, occasionally weighing anchor to explore new coves.
There are kayaks at hand for those who wish to paddle into low-lying caves.
Ha Long Bay's crowds, however, are unmissable. Construction is everywhere, and hotels and casinos are going up fast.
Although the national marine park is vast and supposedly protected as a UNESCO site, up to 500 ferries a day carry day-trippers in and out of the crags and peaks.
In addition, the industrial city of Hai Phong is only a few miles south, putting the onus on tourism authorities to move quickly to prevent this scenic wonderland from deteriorating.
Red River highlights
One of the great benefits of river cruising is that boats can anchor frequently at villages and small ports, either to pick up provisions from the local market or let the passengers take in an excursion or two.
Among the highlights of Pandaw's excursions are water puppet performances, ethnic dancing, a bird sanctuary, Buddhist and Taoist temples and visits with local artisans and craftspeople.
We see several sturdy stone Catholic churches as well, built during the French colonial period.
Visitors will invariably be welcomed to a village home with an offering of green tea.
Or, if it's evening, they might tempt you with a splash of rice whiskey.
A unique feature of the houses we see from the upper deck is that many of them have fake gables.
From a frontal view, it looks like another floor, but it's only a triangular façade with nothing behind it, giving the appearance of small Buddhist shrines atop the roofs.
Almost every building has lightning rods, sometimes four or even six, on the rooftop. They're shaped like spires, which accentuates their pious appearance.
Another unique characteristic of the northern Vietnamese is the custom of burying loved ones in their paddy fields. Although the practice is now banned, thousands of shrines and tombstones still pepper rice fields as far as the eye can see.
Our tour guide explains that the tradition is twofold: firstly, so that the headstone acts a reminder to the family that you are still here, still looking over the household; and secondly, as a warning to your family never to sell this land.
Hanoi and beyond
Half-way into the trip we arrive in Hanoi, Vietnam's capital, a city of over six million people.
After the customary tours of Ho Chi Minh's mausoleum and the inspirational Temple of Literature, it's reassuring to get our legs on land with a walking tour of the Old Quarter, taking in its French architecture, bustling narrow boulevards and cafes.
Soon enough we're back on board and the ship's two 350-horsepower engines roar to life.
With a toot of the horn the ropes are cast off and away we sail.
The Upper Red River veers northwards to China, but we take a sneaky left-hand turn down the Da River (Black River).
This is the scenic part of the voyage: looming lush mountainsides and fresh countryside breezes.
Children scream as they jump into the river; men sit fishing by the banks; women wash clothes in the clear dark water. Rice paddies are immaculately manicured, bordered by banana groves, passion fruit trees and peanut plantations.
Every now and then a fish farm appears, made from rudimentary bamboo poles and nets.
Aside from catfish, anabas and African carp (ca ro phi), villagers on these riverbanks also breed shrimps and oysters.
"Finally got to see what we came to see," says Andrew Baker, 72, an academic from Melbourne and one of the 22 passengers I meet on board.
Onboard the Pandaw
With a passenger capacity of 32, the ratio of guests to staff is almost one to one, which helps explain the meticulous attention to detail.
"Boat's been wonderful; hospitality amazing," says Nina Grace, a tour operator from Sydney.
"I just loved it!" adds Craig Kilgour, a retired minister from New Zealand, over his evening beer. "I can't wait to choose my next trip."
Cabins sleep one or two and feature brass fittings and polished teakwood paneling.
Dining is a thrice-daily feast of East-meets-West flavors and healthy fare.
The day's activities conclude with sunset cocktails on the top deck, followed by an unhurried three-course dinner accompanied by a buffet of salads, cold cuts, cheeses and breads.
For now at least, Pandaw
is the only firm operating cruises on the Red River. The 10-day tour starts at US$2,600, excluding flights.