We did two on our last trip... the result of making new friends after the first. The first only had 23 people signed up online and a bunch from the hotel. The second had like 40, a bunch more from the hotel and a few last minute sign ups. They used the larger boat on the second. Both were insanely fun, but pushed I’d say I preferred first (which was smaller). I found people to be a bit more free, and more people were participating in all the ‘antics’. Just seemed easier to get the party momentum going. Now this could just be the people on board, or even the bigger ship. But in the end I wouldn’t worry about the number of people, and just plan to bring the party.
Just to confirm that even though we only have 15 signed up so far for Mon 9th we will almost certainly be going ahead. Recently the hotel have been sending us an extra 5-10 couples each trip and are going to have a big sales push this weekend.