My husband and I were married in New York last October on the Horizon and it was positively wonderful!! A Wedding For You (mentioned in an earlier posting) coordinated the entire event; all we literally had to do was show up. I highly recommend them.
We had about 30 guests for the ceremony that took place in the Zodiac Lounge then had a great lunch down in the dining room. My family still talk about our wedding to this day. But, quite honestly, the best part was when the guests got off the ship and we sailed away to Bermuda. You literally celebrate for 7 days! And, frankly, it is a steal pricewise, considering the prices of weddings these days (i.e. we were to have a champagne toast along with the luncheon [somthing like a difference of $4 per person to have it]. It was not just a toast, the glasses were kept constantly full. The wine steward (whom we now refer to as "The Champagne Lady") did an outstanding job as did all the dining staff.
I'm not sure what the situation is with the ships that have wedding chapels, i.e., does one contact them directly. So again, let me recommend that A Wedding for You be your guide as they handle not only shipboard weddings but also weddings in special settings, like on the beach, in Central Park, on top of the Empire State Building. Get the idea?
Bottom line?? DO IT!! You will not be dissapointed and you will have the most wonderful memories of your special day.
All the best and I wish you every happiness.