How Can I Best Use Engineers?
A: Engineers can be used to repair ships, or to accelerate the creation of new ships. When you assign engineers to a space dock or other constructor, they will significantly increase the speed at which that constructor builds ships -- up to three engineers can be assigned to each constructor (more can be assigned, but beyond three have a severely reduced efficiency). When you do this, they won't leave the constructor until you tell them to. They can also be assigned to assist ships that are self-building, but they will then go off and do something else when they are finished.
Engineers are mostly very independent-minded. Just place them near the ships you want them to repair, and they will move around doing the repairs on their own (fixing regular health as well as engine health, and helping to accelerate any placed ships that are self-building). They won't try to repair/assist any ship that is more than 15,000 range away from them, but if there are damaged ships that are moving, or which are in a long line across the map, then the engineer might migrate pretty far.
One very helpful technique on planets controlled by your team is to place engineers into attack-move mode. While in this mode they will repair/assist ships anywhere on the map (not just those that are nearby), and when they no longer have anything to do they will return to the attack-move point that you originally gave them.
Engineers can also be useful if you bring them along to battles on enemy planets, since they can repair your ships as they fight. Just bear in mind that their abilities will be more limited here -- after a ship is damaged, it can't be repaired for three seconds after that. If your ships are taking constant, rapid fire, there isn't going to be a lot your engineer can do.
What Restrictions Are There On When An Engineer Can Repair Another Ship?
A: Engineers are not allowed to repair targets under the following circumstances:
1. The target is non-repairable (Fortresses and Force Fields).
2. The target is itself busy repairing another ship.
3. The target took damage within the last three seconds.
There are no restrictions on how many engineers can simultaneously repair/assist any given ship.