travel, sometimes seated and sometimes standing. This is a convenient method of manoeuvring in a narrow waterway or through a busy harbour. The "Rantilla" system of frontrowing oars uses inboard mounted oarlocks rather than a reversing transmission to achieve forward motion of the boat with a pulling motion on the oars. Another system (also called sculling) involves using a single oar extending from the stern of the boat which is moved side to side underwater somewhat like a fish tail, such as the Chinese yuloh, by which quite large boats can be moved. Sampans are rowed by foot in Ninh Bình Province of northern Vietnam. The Intha people of Burma row forwards using their legs. The pletna of Slovenia is rowed forward in the standing position with two oars. Rowing propulsion Rowing is a cyclic (or intermittent) form of propulsion such that in the quasi-steady state the motion of the system (the system comprising the rower, the oars, and the boat), is repeated regularly. In order to maintain the steady-state propulsion of the system without either accelerating or decelerating the system, the sum of all the external forces on the system, averaged over the cycle, must be zero. Thus, the average drag (retarding) force on the system must equal the average propulsion force on the system. The drag forces consist of aerodynamic drag on the superstructure of the system (components of the boat situated above the waterline), as well as the hydrodynamic drag on the submerged portion of the system. The propulsion forces are the forward reaction of the water on the oars while in the water. The oar can be used to provide a drag force (a force acting against the forward motion) when the system is brought to rest. Although the oar can be conveniently thought of as a lever with a "fixed" pivot point in the water, the blade moves sideways and sternwards through the water, so that the magnitude of the propulsion force developed is the result of a complex interaction between unsteady fluid mechanics (the water flow around the blade) and solid mechanics and dynamics (the handle force applied to the oar, the oar's inertia and bending characteristic, the acceleration of the boat and so on). Distinction from other watercraft The distinction between rowing and other forms of water transport, such as canoeing or kayaking, is that in rowing the oars are held in place