Tom -
As you suggest, the term \"overhaul\" spans a wide range of maintenance and repair activity; and the number of required tasks increase in proportion to the time since the last overhaul. The US Navy generally schedules major yard refits every three years, but accidents or battle damage might cause an earlier yard availability. Aside from anticipated routinely scheduled maintenance tasks, a ship generally develops a random list of non-functional auxilliary equipment unrepairable by on-board personnel; awaiting the next tender or shipyard availability period.

The time allowed for an overhaul depends first on the operational requirements for the unit -- very little time is allowed when major operations are pending. Beyond that, the time required is a function of available yard facilities and personnel. Major shipyards can accomplish work in a day that could take weeks in a remote port. And finally, the priority of the ship requiring repairs determines what fraction of yard resources will be devoted to its needs, and whether work will proceed only during normal working hours or around the clock. The amount of work completed might depend more on the time and resources available than on the needs of the ship, and a ship might leave an overhaul period with a few items remaining on its yard availability \"wish list\". =AL=