Thailand has many rivers, with a lot of water, but I don't know the navigable limits. Ocean-going ships can come up Chao Phraya River to greater Bangkok.
I spent today at the national museum.
This was very interesting, but not for river or paddleboat history.
Two royal yachts were ocean-going screw steamers.
The only paddleboat which I saw was a photographic reproduction of a wall mural; included was a small river paddlesteamer (my guess 20 m long), with canopies over the fore and aft decks.
One blurry photo of a river steamer towing a barge seems to be of a screw vessel, not a paddle one.
One emperor/king had strong naval connections. The book of his life shows an ocean-going warship, and a submarine.
The few river photos which I saw showed hand-propelled barges: commoner and royal.
The museum bookshop had books on the WWII Thailand - Burma railway (I ought it) and on the history of aviation in Thailand (a Smithsonian, USA, book). I could not find any on rivers or river history or river navigation.
I haven't started googling on this one yet.
Regards,
Roderick B Smith
Rail News Victoria Editor