When you log in to FishingBooker, click on your name on the top right of the page. Go to Listings. Here, simply click + New Listing, and fill in the details of your boat, just like you did for your original one.
Make sure you list all your boats separately. This will increase your visibility on FishingBooker and will make it easier for anglers to see all the amenities and other details for each boat you have.
Most importantly, listing a boat on FishingBooker is free, so why not use that opportunity and let the world know about all the beauties of your fleet!