There are 14 seats available in each shuttle trip. If the time you want, does not show up as an option: that means that time has been filled. You can only select options that are still open and available. So please don't delay when selecting your shuttle option.
You may also be able to add your boat to the trailer, but please arrange that with Riverside Adventure Company prior to the event date. Space will be dictated by number of shuttles, and number of boats rented for the event.