Don't know if this is a bug or just a feature I never discovered before but if you have a damaged boat then it can repair at sea by doing full rest in its present location. I have a reflex action of sending it home to rest which can take time and expose to risk of attack while travelling. Satellites can also repair by resting them.

EDIT, seems to work for destroyers but not cruisers so probably a bug.

EDIT 2, seems to vary with level of damage, a cruiser with 2 hits can repair, one with 4 cannot.

Yeah, sounds buggy. You should be able to get readiness back, but not hits. 

Perhaps I am confusing lack of readiness with damage, but I am certain ships have engaged in combat, taken damage and repaired by resting at sea; will investigate and get back to you.

My mistake, I was reading the red bar by the icon as damage. Resting restores readiness, as it should, but does not repair damage.