If you want to set up day sails, you should do your research and book on your own ahead of time. If you want to take a tour, you can generally get off the ship and do it on the spot. Most ports have a "preferred provider" of shore transportation, a taxi union that is allowed to pick people up off the pier. To get a better deal, you may have to walk a bit. At Antigua, you will run a gauntlet of taxis in order to get to the "independent operators". Again, find out what the taxi license plate looks like in each port. There are people who "gypsy cab" illegally and there are people who drive minivan buses that will charge a tourist taxi fare. If you know where you want to go, tell them, otherwise you will be taken to a tourist beach. Let the buyer beware!