Shock load

A shock load is a sudden transient force that rises and falls far faster than a machine’s normal cyclic loading, delivering a high peak stress in milliseconds. Sources at sea include a propeller striking ice or debris, slamming in heavy weather, a grounding, the snatch when a windmilling propeller is engaged, and underwater shock on naval ships. Because the load is transient its peak can exceed the static rating several times, and shafting, couplings, gear teeth, and bearings are sized with shock factors for it. Resilient mounts and elastic couplings absorb part of the energy; warship machinery is qualified to defined shock-test severities to survive non-contact explosions.