You mean from Houai Xai to LP or Vientiane, I suppose?
I wouldnt recommend them. Sure they are fast, something like 30-40 knots, but Mekong is no walk in the park in that area, its got a very fast current, twists and turns in a mountain canyon, and underneath the murky water there are lots of deadly, sharp rocks and sandbanks which you simply cannot see.
Because of the current, everything moves around under the surface, and water level changes, too, so any maps are of no use. In fact the skippers ´read´ the water surface and they know where they shouldnt go... normally! That kind of boat will surely be blown to pieces, if it hits a rock at such speed, and if you get knocked out in the process, you are very much likely to drown. These accidents do happen.
We went upstream on a bigger slow-boat, and that was exciting enough sometimes, as they had to make a quick shutdown of the engine to prevent hitting the rocks. They needed to get it back on quickly, too, because the current made the boat go reverse in an eyeblink. Fast boats were entertaining to watch, I can tell you that, they sometimes had to shut the throttle to enter the bends, just like a racecar or bike on a track! Still I´d recommend to use the slower boats. Its a really beautiful area, and better appreciated, when moving slowly.
Oh, and if you decide to go by one, do note that there´s a very remote village about half way between Houai Xai and Louangphrabang (Pak Beng, maybe?) where those slower boats usually spend the night. There they may try to sell you all sorts of illegal stuff thats smuggled up and down the river, but stay away from those. They may set you up with the police, or at least claim they will, and rip you off.
Last edited by pecha72; 10 Sep 2008 at 11:37.