I'm planning on doing a day trip from Dubrovnik to Kotor. The original plan is to drive the coastal road via Perast and then take the ferry shortcut home (Lepetane - Kamanari). According to Google Maps the latter actually takes about 15 minutes longer? Is Google maps miscalculating something or is the scenery on that side of the bay that great, ie is the ferry really worth taking?
We just did this last weekend. We drove into Kotor by going around the bay and then took the ferry shortcut on Sunday on our way back. Going around the bay, the road is fine. Coming back, we used the map on my iPhone and it sent us along the coast directly from Kotor and I will say that quite a bit of that road is very narrow for two 2 way traffic. We had to stop a lot to let cars pass going in the other direction, and once we waiting for someone pulling a camper to figure out how to turn it off of the road into a campground or storage area full of other campers. I was in the passenger seat and laughing at myself for leaning towards my husband, as the passenger side of the car is frequently right on the water, either with a low stone wall or virtually no barrier. Sure, the scenery is great, but I can assure you that neither of us looking at it - all eyes were on the road and oncoming cars. Halfway there, I saw that there is a bigger road that goes to the ferry via Tivat. Do that if you are a nervous driver. The ferry itself was just fine. I believe it was 4.5 euro for our car.
As an aside, we spent two nights in Kotor and it may have been my favorite place in a two week trip (though that's tough call because Ljubljana and Rovinj were so great too - and I really like Split and Dubrovnik...), so I would have hated to only do it as a day trip. And check to see how many cruise ships are in port before you pick your day.