Abstract: A multi-impact jarring apparatus for retrieving objects stuck within a well bore comprises (1) an operating mandrel reciprocatively mounted within an upper housing attached to a fishing operating string, the mandrel acting as a hammer against the housing for creating a series of successive upwardly directed impact forces, (2) a releasable spring compressible between the mandrel and an upper portion of the housing and responsive to tension applied to the operating string, (3) releasable latching means for releasing the mandrel from the upper portion of the housing when the latching means is moved past a preset release position. The movement of the mandrel responsive to tensional force of the operating string allows for sudden release of the release spring and causes sudden upward movement of the mandrel resulting in impact of the mandrel against the upper portion of the housing and in immediate reposition of the latching means to reconnect the mandrel and a bottom portion of the upper housing body.

Abstract: A remotely-adjustable, downhole fishing jar of the mechanical type is used within a well bore for freeing stuck pipe or tools. The jar, while downhole, can be set or reset by an operator at the surface for each firing stroke for any desired impact force within the capability of the finishing string to apply tension to the jar. A selected amount of tension to the fishing string is applied by the operator to set in a mechanical memory of the jar the desired impact force.