I was planning to take the dogs with me on a short visit and wondered if anyone could advise on what's involved. Will they need pet passports?

No you dont need a pet passport we travel to southern Ireland to show and to the north and never had a problem .
Dogs stay in the car while you are on the ferry .

Technically from 1st January 2012 dogs DO require a passport to travel but DEFRA site says no one is enforcing this rule and therefore people are unlikely to see any changes when traveling. That said if stopped and you didn't have paperwork it is not clear what would happen.
Dogs remain in car on the ferry

Last time I did it was in March and it was Ire-UK, as pet passports are free here I had mine with me but nothing was asked for.

Free travel to Ireland, only thing is you have to fill in a form at the port, if you are travelling with more than four dogs, due to  the puppy trafficers, but really quick and simple to do....enjoy your trip.

Who needs the form is it the border control?
What questions does it ask on the form please?

i went over to Ireland in August with my show team.. nobody asked how many dogs we had.. and yes they stay in the vehicle or there is kennels on board if you want to use them..

You complete the form at the port office, name vehicle registration number and booking ref, number and breed of dogs, its as simple as that..seems more of a paper exercise.

I recently travelled as a foot passenger with dog so had to use the on-board kennels. Just thought id post that Stenna ferries have cctv set up on the kennels which you can view on a screen at any time on board the main passenger deck. Was a pleasant suprise for us as we had been worried about leaving unattended.