At C&I there is a window near the entrance/exit for port authority. If there is someone there and if they decide to work, they will ask each group coming through C&I where they are tied up. If you are on the port authority dinghy dock at the ferry wharf then they will collect the $6 fee. I've never had someone try to collect it at the dinghy dock.

We started staying away from the dinghy dock at the ferry wharf for a couple of reasons. The catamaran ferries are kept tied up right on top of the west side dinghy dock and the ferries have hit tied up dinghies on more than one case. There are also some very large tenders, 16+ feet, that will tie up and block access out unless you want to go under the ferry. Crazy stuff happens, but at least St. John Spice has their SpiceCam overlooking that side. The east side dinghy dock has much less visibility, no lighting and there has been a lot of pilferage and theft. Both docks get a lot of abuse.

http://www.stjohnspice.com/spicecam/

The NPS dock is concrete and has cleats that you can lock your dinghy to. There is a lot of traffic, lighting, clear visibility, the NPS visitor center is nearby and the Park Police are in and out all day long. There are also NPS trash cans for dumping garbage and a lockbox for paying the NPS mooring fee. Free too.

You can always pull your dinghy up on the beach and lock it to a tree. But, it will likely be a playground for kids and the dogs will decide its a great spot to mark. You also have to mind the swim buoys (eww, not in that water).

Cheers, RickG