Automatic lock for telescoping joint of a riser system

The field of this invention relates to selective locking systems for telescoping joints in offshore riser systems. An automatic locking mechanism for a telescoping joint for a riser functions in several modes. In an operating mode, the joint is free to have its inner and outer barrels move with respect to each other without engaging each other in a locking relationship. In a second position, the telescoping joint locks when it is fully retracted. In a third position, the system locks the inner and outer barrels together to hold them in a fixed position. The inner and outer barrels are locked when a movable sleeve is properly positioned to allow spring-loaded dogs to be biased through windows in the sleeve so as to act as a landing shoulder to catch a groove on the outer barrel. By putting the actuating sleeve in a variety of positions, the various modes of the locking assembly can be deployed.