The world's most vexing question: should I tip when I go overseas? [View all]

It's awkward, I never know if I'm giving too much or not enough, and is a US cruise ship going from Sydney to Hawaii somewhere I'd be expected to tip seeing as how they have that weird no alcohol for under 21's on it? And I never know when to leave a tip. Do it when they're not watching, or make a big deal of it? It's enough to make me nearly want to change my plans and opt instead for a Booze Cruise on the Dianne Brimble Death Ship where there won't be any confusing stuff like that!