In my opinion they should simply charge a daily rate of the price for the cruise from those passangers that they find in the Yacht Club that don't belong there and send them out afterwards.
It is easy to identify them as most YC guests will wear their wrist band, and others can be checked for a cruise card. Even if one would come up with the argument that regular YC guest should not be harrassed by controls, i'd say that the staff nearly knows any YC guest anyway, since they are trained to and have to remember their names anyway.