Like a previous poster said, find a sailing that is also a singles cruise. You can book with the singles cruise company or book it yourself.
Most of the singles cruises use name beads to identify their members. Show up at a bar or nightclub and look for name beads. It couldn't be any easier. The phrase shooting fish in a barrel comes to mind.
Even if you're not looking to hookup, a singles cruise is a great way to travel solo but still feel part of a group and not like some weird outsider like you might on a normal cruise.