OH is hoping to retire this year and is very keen to visit Ireland again.
We would want to take Tommy the dog and have so far travelled with Corsica Ferries who allow dogs to go pretty much anywhere. Having looked at Irish Ferries and Brittany Ferries, it seems that your dog stays either in the cabin or in the car/kennel for the whole of quite a long crossing.
Irish Ferries have pet lounges but as far as I can see, they’re only on Ireland - UK routes.
Does anyone have experience of this please?
We’ve used Brittany Ferries to the UK and Rona stayed in our cabin with us, which we think is very pet friendly (nb not all their ferries offer this). We travelled overnight, which I prefer as I get very queasy very quickly and I’d rather sleep through the journey and she settled down quite happily between the two bunks (we brought her own bed).
They have an exercise area outside on the deck, so you can take your dog out as often as you like. Rona only widdles and poops on grass that she likes so held it all in for the 12 hours we were on board. Some of the other dogs seem to be more relaxed. Not all - one man told me his dog held it all in for 30 hours on the route to Santander!
BF require dogs to be muzzled when outside of your cabin. I wasn’t sure how she would cope, so decided NOT to practise with it, but just put it on her before she got out the car - she was fine. I’ve got the plastic cage type muzzles which give the dog plenty of space to open their mouth and pant if they need to.
Thank you Sue, that’s helpful. I noticed about muzzles so we’ll try that out on Tommy.
OH is mulling it over about spending 14 hours either in the cabin or the outside dog space - I’m not sure how he or Tommy would take it, even if they were asleep for some of the time. Travelling with Corsica Ferries as our first dog/ferry experience has spoiled us. 
We obviously weren’t asleep for all the 12 hours. We had a couple of light throws that we put over the bunks so she settled down on one or other of the beds while we read or chatted. We thought we might take her (muzzled) with us while we looked round the various restaurants/bars but we were turned back at the entrance.
It meant we didn’t eat together. I stayed in the cabin with her while he went and ate and then we reversed roles.
We would not want her in a cage and leaving her in the car would invite some serious chewing!
We travelled Roscoff to Cobh on Friday night in a pet friendly cabin on the Pont Aven. We were loaded first, so in our cabin by 9:30. Our dog is 14kg, not huge but we saw some very big dogs & some passengers had 2 quite big dogs - not sure how they managed as the cabins are quite small. There is a pet exercise area at the end of the corridor with bench seating for humans. As it was an overnight crossing we only sat out there in the morning - our boy did not use the “facilities “ but was happy to wait until after the port where there is a small park & easy on road parking. We didn’t leave him alone in the cabin & took turns to have breakfast. I suppose it depends on your dog but other people left theirs alone. We’ve done this crossing before without the dog & it was not really different this time except for eating alone. We will return on a Saturday (here for 2 weeks) & hope it wi be as easy. There is another ferry on this route but haven’t used it.