The ancient Dock of Royal Barges stood on the north bank of the old Lopburi River (presently named Khlong Muang or City Canal) opposite the Grand Palace between Wat Choeng Tha and Wat Phanom Yong.
In the "New Historical Relation of the Kingdom of Siam" written by de La Loubère we read that the ancient dock was divided in separate trenches each locked up in a wooden and roofed enclosure.
Their arsenal is over against the palace, the river running between. There every one of these barges is locked up in a trench, where into runs the water of the river; and each trench is shut up in an enclosure made of wood, and covered. These enclosures are locked up, and besides this is a person watches there at night. [1]
There were 20 barge houses adjacently situated, from the mouth of Khlong Khu Mai Rong to Wat Choeng Tha. [2] The Kalahom or Minister of Defense was in charge for the dock. [1] The dock and the barges were destroyed in the Burmese attack of Ayutthaya in 1767. No visible traces remain of it and the landscape has been unfortunately largely altered.
On Vicenzo Maria Coronelli's map published in 1696, we find the word "Arsenale" east of a canal or river. It remains unclear if this was the location of the Royal Barges Dockyard near Khlong Khu Mai Rong or the location of Riverine Vessel Dockyard, situated at Ban Wat Tha Ka Rong on the Chao Phraya River. The latter provided shelter for approximately 200 vessels. [2]
References:
[1] A New Historical Relation of the Kingdom of Siam - de La Loubère - page 98/99. [2] Discovering Ayutthaya - Charnvit Kasetsiri & Michael Wright (2007) - page 297.