Technological level - similar to contemporary. Yes, I mean a watercraft, mostly big cargo carrying ships. I mean only calling for help while being in middle of ocean and not being within line of sight distance of shore transmitters.
Seemingly straightforward question, except:
flare stars and telecommunication satellites do not mix well, and low population density means that local population would not afford frequent satellite replacement
sure, they can use good old fashion radio... except that flares tend to knock out ionosphere propagation window for short waves and bring extra background noise on medium waves (if this premise is incorrect please correct me in answer)
any system that uses insane amount of energy has limited functionality as it requires ship engines to be fully functional (you can only call for help if you ship is in good shape, sure it's better than nothing...)
a suggested system can not be more expensive than just accompanying each cargo ship with a small, ocean worthy emergency rescue ship