Hi Josh, welcome aboard! It sounds like you're getting ready for a wonderful cruise on the Fantasy to my favorite place in the world: Castaway Cay! You are going to absolutely love that island. There is no place in the world quite like it.
Castaway Cay has many different
water sport options and rentals, including the water trikes and paddle boats. You can log in to your reservation online, choose your Castaway Cay day and add a Port Adventure. Though these are technically just rentals, they are considered Port Adventures for pre-booking purposes. The good news is that you can even decide that day on Castaway Cay to rent a trike or paddle boat and you should have no problem getting one.
The rentals are for 30 minutes each and run $15 for a water trike and $8 for a 2-seat paddle boat, or $10 for a 4-seat paddle boat. Both of those are fun ways to spend a bit of time in the crystal clear waters on the island! Be sure to check out the Snorkeling Lagoon too, as Disney has hidden some fun surprises to see under the water!
Have a fabulous cruise, Josh!