i just completed this section by bicycle. was waiting in xieng dao for a boat but no luck so decided to be adventurous. this is a total of 30km with only 7 km of single track. only took three hours on a mountainbike. from xieng dao the road starts at a fork at the point you would head downhill to the boat ramp. there's 10km of smooth dirt road, then a small water crossing (2 meters, 10 cm), another 7 km of dirt that gradually deteriorates (some landslides, all cleared) until the bridge over the nam tha. the bridge is a standard iron with wooden deck, with two strips of wooden planking. it's been there for at least 30 years. cross the bridge and you're immediately on single-track. dense vegetation very close in, but no problem for an mtb with panniers. no major climbs, actually pretty easy. a couple downed trees you'll have to go under, with at least 1m space. this section is about 7km with one dry water crossing. a bit difficult to get up the west side...was able to slowly push a loaded bicycle up. there were no cross-trails to cause confusion. the track comes out onto a standard dirt road. at this point the road appears to head uphill following a wash. otherwise, a good dirt road for the final 6km into xieng kok. just before entering the village, there is a 10m wide water crossing. currently less than 15cm deep. if coming from the xieng kok side, note there are two villages about 2.5 km apart. xieng kok mai has the boat ramps and guesthouses. xieng kok kao has the access road to the trail. from the main road, take the only good dirt road south, about 500m downslope through the village where you'll hit the water crossing. i have photos but still travelling and no way to download. will be able to post photos and answer any questions upon return to chiang mai around the feb 10th.