A Maple shortbow (u) is cut from maple logs at level 50 Fletching, granting 50 experience. An unstrung maple shortbow can be strung using a bowstring at 50 fletching, granting an additional 50 experience for a total of 100 for a single bow. The unstrung bow then becomes a maple shortbow.
It takes 15 seconds to string an inventory of 14 shortbows. With banking time, this means players can potentially string 3 inventories a minute, which is 180 inventories an hour, for 2,520 bows in total. This means that the experience gained per hour is roughly 126,000 Fletching experience.