Boost Fin is a fin with a propeller for surfing or paddle boarding. It comes with a control watch with two big buttons that you used to control it or cut it on and off. Also you can customize it with the app on your iPhone. You can make it where only cuts on for the paddle out and then give you 3 to 5 second boost into waves, Or you can ride it for an 1 hour and 45 minutes straight exploring on your Paddleboard. It comes with four adapters so it fits all Fin set up for all boards. The only reason I'm selling it is cause I moved away from the coast. It's only been used once so it's practically brand new and originally it cost $750 plus $40 for each adapter so close to $1000 package that your getting for ONLY $350! Won't last long