Ferry around Ireland

There is no such service for many reasons, not least the amount of time it would take compared to other, more direct forms of transport. If you want to cut down on driving, you could take a bus or train from Cork to Dublin for starters.

Public transport is not Ireland’s best feature.

The reality of making the best use of your time and actually seeing Eire is by car. Otherwise long and often inconvenient bus rides.

Never taken the train so I’ll leave to other posters to comment.

That said here’s link to a map of Ireland’s Ferry ports.
http://www.irishtourist.com/travel-info/ferryports-in-ireland/

Never used a ferry for transport either so can’t comment. Hopefully other posters who have made use of them will offer intel.

Is it the driving on the opposite side of the road that is your concern? I’ve driven the entire island including NI twice solo with a clutch. Sometimes it pays to have been born when Truman was in office because we were taught how to drive with a stick shift.

Honestly, it is not as frightening or unnerving as you think. You merely go slower and stay focused.

Right - no ferry.
I agree with Claudia that the best way to accomplish your itinerary is by car. Booking one with automatic transmission (which you'll have to specify - the default rental is a manual) would help alleviate much of the challenge of driving on the left.
If you prefer to use public transportation then your better option is probably the train. Though Ireland's train system isn't the most robust in Europe, it will get you where you want to go with a minimum of hassle as long as you're aware of the limitations in the service area covered.
Given the very little time you have available I'd suggest picking a couple of bases - Killarney and Cork maybe - and relying on day trips and organized tours from there as you work your way back to Dublin.

thank you, so we can rent a car and drop in Dublin. We are staying in Kenmare for sure, and trying to decide where in /around cork kinsale /cobb to stay, 2 nights. i will look around more for places to stay there.

Yes you can rent a car and drop in Dublin. I’d drop it at the airport and bus into Dublin. Investigate AirLink.

Know in advance that not returning the car to Shannon will cost more though. Just the way it is with car rentals. Also take every bit of insurance you can for the rental.

Why both Killarney and Kenmare? Very close to one another so curious if staying overnight in both or merely mentioning areas you plan to visit.

Lastly, don’t miss seeing Glendalough in route to Dublin.

If you'll have a car then I'd suggest the pretty seaside village of Kinsale rather than Cork or Cobh. It's a pleasant place to wander around - much nicer than the congestion of Cork, and you can always visit Cobh as a day trip.
The prettiest part of the ROK (IMO) is the section between the Gap of Dunloe and Waterville, which includes the very pretty (and uncrowded) Skellig Ring Road near the village of Portmagee. Unless there's an overrriding reason for you to stay in Killarney town I'd suggest finding someplace near the Gap to facilitate easy explorations by car and avoid the tourist crush in Killarney.
You're really going to have to budget your limited time carefully to make the most of it and not spend most of your trip behind the wheel. Maybe 2 nights each in Kerry and Kinsale, then a leisurely return drive back to Dublin. Cashel, Kilkenny, and/or Glendalough would be good stops along the way.
Good advice to drop at the airport and Airlink or taxi into town - you really don't want to drive in Dublin city traffic.