Park for free on the street in Jamestown, and take the ferry to Newport. You can find spots in Jamestown a few minutes walk from the ferry. Nice view on the boat. Nice narration during the trip.
The water cools you down on a hot day. In most parts of the boat you will get a little sprayed by the water. The center seats and the front are probably better if you don't want any spray.
The only negative is if you arrive in Newport somewhere other than Waites wharf, such as Perotti park, and get the return ferry from Waites wharf, it is really hard to find the ferry location.
Waites wharf has a complex solid wharf and a complex floating dock. You go on the floating dock to the right. The only Jamestown and Newport ferry sign does not make it clear which of these you should follow to the end, the solid wharf or floating dock and there are no other signs.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.