Once you find the option that best meets your needs all relevant information will be stated on that specific listing. You will be able to see all details such as trips, rates, amenities, short captain's bio and the location of the departure site.
The location is shown on a map at the very bottom of the listing. You can either scroll all the way down to access the map, or just start scrolling down a little bit until a black header appears on the top of your screen with several options on it, one of which is the location of the boat.
The departure location will also be stated in the confirmation email after your trip is confirmed. Also, you will be able to see the boat's location online when you log in to your user account and go to manage your booking.