I had trouble with the Mull ferry which can take between 4 and 6 vehicles depending on size and we're packed in pretty tight. The passenger seating area is very narrow and bringing a fullsized bike inside would have been a significant impediment to getting to the safety exits. Bike had to stay on the car deck and there wasn't a secure attachment site and the transportation guys didn't want it locked to the boat. I also had issues with some of the smaller island ferries like Musa, Fair isle and Isla. Some of the boats we have to hire and they are essentially small fishing vessels, or as we called them "Shetland Uber"