First, they typically med moor, so the width isn't a big issue for fitting unless the marina is jam packed and they simply haven't got enough space. There are rarely fixed finger piers limiting who can fit. At worst, you may need to adjust dock lines and shore power
cords if you don't line up quite right.
Extra cost for a cat is more common in the med vs the US east coast
, though it's not universal. We were in Spain
for a couple years and didn't get hit with a surcharge on a 10m Catalac
For the big cats with a 20-25ft beam, a surcharge makes perfect sense when med mooring
as you are taking up more space than a similar length monohull.
If you get a narrow cat like a Gemini
(14ft beam), it's not really any wider than a monohull. You could try simply giving the boat
dimensions when calling for a reservation and not mention that you are a cat (they aren't common in Europe
so they won't instantly know what it is by the brand name). We had good luck with that on the US east coast
. A couple times they pointed out that we were a cat upon arrival and we asked them what we get extra vs a 14ft beam monohull that they assumed...they always dropped it. No guarantee but had good luck with that approach.