Running gear for inboard cruising boats is that gear outside of the hull that provides drive and direction. For inboard boats, that includes a portion of the drive shaft that protrudes from the shaft log, struts that hold the shaft in place, the propellers, and the rudders.
The belts that drive your engines accessories, which often include the raw-water pump, circulator pump, and alternator, will typically provide reliable trouble-free service, provided they are properly maintained and replaced when approaching the end of their useful lives. Many cruisers neglect this all-too-important component until disaster strikes. Once the belt breaks, all of these vital systems grind to a haltliterally. The raw-water pump stops pumping sea water, the circulator pump stops circulating coolant, and the alternator no longer produces electricity. While you may not immediately notice the loss of an alternator, rest assured, you will quickly become aware of the loss of sea water and coolant as the temperature gauge climbs into the red and the overheat alarm sounds. (Your engine is equipped with operating versions of both of these instruments, right?)