My brother and I spent 8 nights on that boat. And we are very lucky for that unique experience. The boat has everything you need. It's just perfect for a cosy and calm stay. It gives you the perfect holiday feeling.
Showers aren't on the boat, but very near the port (3 minutes walk).
To go downtown you need to take the metro, which is a 15 minutes walk from the port away. But there is a big shopping mall maybe 10 minutes from the port, which has essentials things like supermarkets and clothes stores.
My brother and I decided to rent a scooter, what probably is the best in a city like Barcelona. It's so easy to get around with it, we totally can recommend it and also the boat!