In section, a yuloh can be found with flat side up or down. The oar reverses pitch easily at the stroke's end. Theoretically, however, flat side up is more efficient. When an oar has its curved side down, lift works in the direction of the boat's travel. Only yulohs, however, can take advantage of this, as the string does the twisting.
Free oars are almost uncontrollable with the curved side down.
Yulohs can be very large. Worked with gangs, with one or two pulling on the rope and three or four pushing and pulling the oar back and forth, they can run 25 or 35 feet long in sampans of 50 or 60 feet. The Chinese don't seem to use yulohs on small boats, and a Western-style oar is probably better suited to boats under 16 feet unless they are heavy powerboats or sailboats. He claims 2 knots in a calm, not bad for a 5-ton boat. Vertical Stroke Oars Oars for the vertical or slalom stroke are much less specialized.