Can you hire a motor boat for the day?

If you go to Bosa Marina you'll find the Bosa Diving Centre. If you want to learn diving they teach you. But they also hire out boats. Go to their site for more information.

If you hire the boats you can only go Northbound towards Alghero. This is to ensure the safety of the crew as maestrales (South Westerly gales in the Summer) can make a return journey from the South very difficult. It's definitely worth hiring and you don't need a motorboat license (although always good to have!)