It depends on what age group you're in as to whether there will be any reasonably attractive women.
Just remember tho that these singles events are no different than real life. For eg: you go to a bar or club. There's probably 10 guys for every single woman. Of those .1 that are reasonably attractive, there's either a line up of guys hitting on her or she's a total snot and won't give you the time of day anyways.
I hear Meet Market Adventures has some reasonbly attractive women but I went to a couple of the Single Gourmet dances and believe me, they don't call them the K nine club for nothing!!!
I also belonged to another singles dating site and was actively involved with many of the other members (some turned out to be my closets friends) and we held parties all over N. America. At these parties the ratio was about 10 to 1 (men to women) and of the 25 or so women that showed up, 3 were what you would commonly consider attractive (1 or 2 can be considered hot but again, every guy was trying to make time with her).
The ONLY way I would go on one of these cruises is if a) you weren't looking to hook up, just be with like minded people and b) you got a private berth (because most of these tours bunk you with another single guy)