I visit Luang Prabang many times. I come to this lovely town by plane, bus and boat. The river journey by boat is by far the greatest. Take your time and travel 2 days from Thai border to Luang Prabang by a local barge called in Laos the slow boat.
I leave the highway 13 on my way to Champasak. After 5 km I reach the east bank of Mekong river. The local ferries have different shape and size. The smallest ones look like a wooden fishing pier. Such small ferry can carry 4 people and 2 scooters.