It's obviously not a huge deal, but Cobh People's Regatta is on this weekend
http://www.cobhpeoplesregatta.com/
and it will be drawing in a certain number of people from Cork City, especially with the addition of the aerobatics display.
Trains might be full enough over the weekend.
Unfortunately, much of the firework display on Sunday night will have to be watched as the last train pulls out of Cobh station.