If you are organising a boat tour with people you do not know, to ensure that everything runs smoothly, it is a good idea to find out something about your potential tour companions to determine how compatible you are.
To help you find out something about the persons requesting to join your tour, you can ask for and surf their facebook wall to see their types of posts and comments, or you can try this online personality compatibility test. You could email them the questions in the form and fill in their answers next to yours, and study the results at the bottom. To help you email them the questions you can copy/paste them from the webpage or download them here. In case it opens in your browser, you can download the zip file instead.
Note that the person you are emailing with may seem wonderful, but later you find out you do not get along with their partner or other friends, so you may request to test all of them separately.
Hope your trip turns out super excellent!