From: Georgetown, Texas, USA
Shipyards repair ships in a set sequence, based on priority, triage, type. If the player does not supply a priority, ships are repaired 'in order" within type and triage. Type is carriers first, then BB, cruisers, etc. Triage is those in danger of sinking first, then those that can be quickly repaired, then the long repair jobs.
Unless something changes, the same ship will get selected first for repairs each time. This means that one ship will get repaired faster. Then another will move to the top of the queue and be repaired. Players can use priority to adjust the repair order.
If excess shipyard capacity exists, the shipyard will dedicate it to ships under repair (in order). This can effectively give a priority boost to one (or more) ships.
Remember that the two higher priority settings use extra shipyard resource. The two lower ones do not. If you want to manage repair order without spending extra shipyard capacity, use Normal and Low.