The boats were discovered in 2025 when a farmer was renovating a fish pond in Cong Ha neighbourhood, now part of Song Lieu Ward.
Radiocarbon dating suggests the vessels date to around the second century AD, during the late Dong Son period.
Researchers presented their latest findings at the 2026 National Archaeology Conference in Hanoi, following a year of further investigation.
Shipbuilding specialist Do Thai Binh described the discovery as an important archaeological find deserving careful preservation and public display.
He believes the structure consists of two connected hulls supporting a larger platform above. Its construction suggests it was more suited to sheltered rivers than open waters.
Binh said the upper structure, estimated at more than 100 square metres, may have served as a living or gathering space for high-ranking individuals. He suggested the vessel could have been propelled by oars and poles.
However, archaeologist Nguyen Viet, director of the Southeast Asian Prehistory Centre, questioned whether the remains belonged to a conventional boat.
He noted that the structure tilts by around 10 degrees, has a relatively level bottom and lacks clearly distinguishable bow and stern sections.
Researchers have also found no conclusive evidence of propulsion equipment or towing arrangements.
Viet suggested it may instead have been a floating structure connected to the riverbank and called for further excavation to investigate that possibility.
Meanwhile, researchers have analysed soil samples from 12 compartments to identify preserved plant remains and assess whether they were transported goods or natural deposits.
Dr Nguyen Thi Mai Huong of the Institute of Archaeology said waterlogged, oxygen-poor conditions and protective mud sediments helped preserve the organic material.
Preliminary analysis identified seeds, fruit remains and wood fragments from several species, including apricot, plum, Dracontomelon, Canarium and chestnut.
The remains were found throughout both structures, with higher concentrations in compartments thought to be towards one end, suggesting that some areas may have been used for storage.
In the first structure, researchers identified chestnut fruit stalks, chinaberry seeds, Dracontomelon seeds, apricot and plum shell fragments, and 48 unidentified seed specimens.
The second contained denser deposits, particularly in compartments five and six. Compartment six alone yielded 1,842 seed and fruit fragments and 255 unidentified wood fragments.
Other finds included gac seeds, screw pine bark, Chinese honeysuckle seeds and remains from fig-related species.
Across the samples, researchers identified 129 Dracontomelon specimens, 53 chinaberry seeds, 31 Canarium seeds, 30 jujube seeds and 11 acerola specimens.
The discovery of 13 chestnut fruit stalks was particularly noteworthy because chestnut trees are commonly associated with upland areas.
Huong said their presence in the lowland site could indicate exchanges between mountainous communities and the Red River Delta.
Researchers also identified 28 silk-cotton tree thorns, possibly deposited naturally when the structure was moored near riverside vegetation.
The team cautioned that not all the remains necessarily represented cargo.
Researchers identified Canarium, chestnut, Chinese honeysuckle and gac remains as likely cargo, while tree thorns, vines and wood fragments appeared to be natural deposits. Other seeds may have come from either source.
According to Huong, the combination of tropical forest products and plants associated with cooler upland environments offers further clues to possible river-based trade networks in ancient northern Vietnam.
